A review is given on the Shubnikov-de Haas (SdH) effect (i.e., an oscillatory variation of magnetoresistance) and its application to II-V semiconducting compounds. First, the origin, conditions of observation and quantities measured in the SdH effect are discussed in connection with the band structure of semiconductors. Subsequently, some SdH results obtained for such compounds as Cd₃As₂, Cd₃P₂, CdSb and solid solutions of II₃ - V₂ semiconductors including Mn-alloyed materials are presented.

Interband optical transitions and optical lattice modes are presented and discussed in terms of real tetragonal symmetry of Zn₃P₂ crystal. Data of defect-related optical transitions in this compound are also shown.

Pulse deposition at room temperature was applied to obtain CdSe thin films from an aqueous bath consisting of CdSO₄ and SeO₂ on titanium substrates, employing a range of current densities from 80 - 550 mA cm^-2. The films were polycrystalline with a hexagonal structure. The pulse deposited films were observed to show greater uniformity and large grain sizes than the conventionally deposited ones. The films, heat-sensitized and vacuum annealed, showed a flat-band potential of -1.17 V (SCE) and a high energy conversion efficiency of 6.3% at 60 mW cm² in polysulphide redox after photoetching. The optical band gap was 1.7 eV.

The basic requirements of a good thin film photoelectrode for high efficiency photoelectrochemical (PEC) cells are low resistivity and large grain size. The large size grains lead to a reduction of the grain boundary area of the thin films, with important consequences for efficient energy conversion. The low resistivity of the photoelectrodes is required to minimize the series resistance of the PEC cell which leads to lower short circuit current. In addition, we have to tailor the band gap of the material further by adjusting the composition x in the alloy CdSe_1-xTe_x. Low resistivity in the materials can be achieved by a careful control of the stoichiometry of the material or by doping with a proper trivalent dopant such as Ga or In. The control of the stoichiometry and the dopant concentration can be achieved by a careful control of the rate/s of deposition/s. The deposition rates should also be kept comparatively low and also the substrates should be heated to elevated temperatures so that the films formed consist of large size grains. It is advisable to also change the angle of deposition from normal incidence to an inclined deposition so that the films will tend to grow with columnar grains, which are very essential. The grain size can be further increased to some extent by carefully annealing the films in vacuum at pre-determined temperature and for a time interval. The large grain size films formed this way should be coated with very thin layers of oxides like TiO₂ or In₂O₃ to prevent corrosion of the thin film electrodes when used in the PEC cells. Thus, by carefully controlling the various parameters as outlined above, it is possible to obtain high efficiency photo-electrochemical solar cells using these Cd-Se-Te ternary alloy thin films as photoelectrodes.

Analytical modelling of implanted Buried Channel (BC) and Surface Channel (SC) MOSFETs and MESFETs is difficult since the highly non-uniform channel doping profile cannot be integrated analytically to obtain the charge-voltage characteristics of the channel depletion layer. The present paper derives a general approximation to the non-uniform profile which gives simple and accurate closed form expressions directly in terms of device parameters for the various characteristics of all the FETs under all implant and bias conditions (the implant may be shallow, deep or multiple, and it may be partially or fully depleted depending upon the bias conditions). The derivation does not make any a-priori assumptions about the shape of the approximate profile. Instead, the shape emerges from a new formulation of the analytical modelling problem. It is shown that the necessary condition for analytical modelling of all the three FETs is the same, namely, expressing the depletion layer voltage drop V_d as a polynomial of the depletion charge Q_d, where the degree of the polynomial can not exceed two. Next it is demonstrated that such a polynomial for the V_d - Q_d characteristics of implanted FETs can be obtained by approximating the doping profile by a 'shifted-rectangle' profile whose parameters can be derived directly from implantation parameters.

Thin films of doped and undoped Pbo.8Sno.2Te were grown by flash evaporation onto Kbr and mica substrates kept at 400 degree(s)C. In order to grow doped films, the polycrystalline charge containing different concentrations of indium, thallium, bismuth, and antimony was used. The dc conductivity and Hall coefficient measurements were made on these films. Indium and bismuth doped films were found to be n-type, whereas undoped, thallium and antimony doped films were found to be p-type.

This paper deals with the photovoltaic behavior of the indium tin oxide (ITO)/silicon (single crystal) heterojunctions prepared by spray pyrolysis technique. The dependence of the photovoltaic properties on process temperature (T_p) and on the oxidation time (t_ox) have been studied. ITO on p-Si yielded ohmic contact. A photoconversion efficiency of 9.4% is observed (under GE-ELH illumination of 100 mW/cm²) for both small (0.04 cm²) and large (1.0 cm²) areas of ITO/n-Si junctions prepared at a temperature of 380 degree(s)C and for an oxidation time of 60 sec. The junctions are observed to be quite stable with time. An attempt is made to understand the interfacial oxide layer (SiO_x) and its effect on the photoconversion in these junctions.

Cadmium sulphide thin films (equals 3.4 micrometers ) doped with 0.25 wt % As concentration were deposited onto a well-polished stainless steel substrate by an electroless chemical deposition process. The photoelectrochemical (PEC) cells were fabricated using both H₂-annealed and etched samples as a photoelectrode, sulphide/polysulphide as an electrolyte, and graphide as a counter electrode. The cell was illuminated by a 100 mW/cm² light intensity, and the performance of a cell in terms of cell parameters, namely, short circuit current (Isc) open circuit voltage (Voc), junction quality factor ((eta) ), series and shunt resistances (Rs and Rsh), efficiency ((eta) ), fill factor (ff) and barrier height ((Phi) B), has been investigated. It has been found that the cell generates maximum power output when the CdS:As photoelectrode is subjected to a hydrogen atmosphere at 250 degree(s)C for approximately 1 hour and etched with a CuCl:KCN system for 20 seconds. An attempt is made to explain these observations on the basis of a modified surface, improved crystallinity, and enhanced conductivity of the samples.

The A₂B₂O₇ pyrochlore compounds exhibit a wide variety of interesting electrical transport, magnetic and thermal properties due to the diverse possibilities of substitution at the A (rare earth, R) and B (transition metal) sites. While for R equals Nd, Sm and Gd the behavior is metal-like, in most other cases it is like that of a degenerate semiconductor with a thermally activated mobility probably arising from the hopping of small polarons. This is evidenced by the typical T^-1/4 variation of the hopping conductivity at low temperatures and a difference between activation energies derived from conductivity and thermopower measurements. Magnetic ordering of V⁴⁺ ions is clearly seen in R₂V₂O₇ pyrochlores whereas with R₂Mo₂O₇ compounds this is true only for R equals Nd, Sm and Gd. The ordering could arise from Mo⁴⁺ ions. In the case of Y₂Mo₂O₇ as well as for R equals Sm and Gd maxima in susceptibility are accompanied by a difference between zero field and field cooled magnetization in low applied fields. This is characteristic of spin glass behavior. For R equals Tb, Dy and Ho deviations from Curie-Weiss behavior are seen below 20 K, while for R equals Er, Tm and Yb simple paramagnetic behavior persists down to 4.2 K. Magnetic and heat capacity results also point to the existence of Schottky anomalies arising from crystal field effects at the Mo⁴⁺ and R³⁺ sites.

The steady state distribution function of charged carriers which takes into account the energy absorbed by the carriers in an electric field is described. Velocity-field characteristics so obtained agree well with the room-temperature experimental data for silicon samples of varying ohmic mobility. In the nondegenerate approximation, the saturation velocity obtained is comparable to the thermal velocity of the carriers (1.03 X 10⁷ cm/s for electrons and 1.00 X 10⁷ cm/s for holes), a result which is independent of the low-field mobility of the carriers, consistent with the experimental observations. The asymmetrical distribution function favors holes in the direction of the applied electric field and electrons in the opposite direction. Therefore, on a tilted band diagram, electrons tend to sink and holes tend to float, thereby reducing the effective bandgap. This increases the number of intrinsic carriers with the increase of electric field. An effective hot-electron temperature which accounts for this increase in carrier concentration also increases with the increase in electric field. Effective bandgap, effective hot-electron temperature, and carrier multiplication factor as a function of electric field are analyzed for various doping concentrations. The results so obtained extrapolate well in the limit of zero electric field, when well-known ohmic behavior is reproduced. The implications of this carrier multiplication on pinchoff condition, noise behavior, breakdown characteristics, etc. are discussed.

Metallorganic chemical vapor deposition is a practical technique for the preparation of III-V epitaxial layers used in the fabrication of microelectronic and optoelectronic devices. The usual Ga and As sources for GaAS epitaxy are Ga(CH₃)₃ and AsH₃, respectively. However, the use of these precursors has some disadvantages related to the toxicity and storage of arsine, stoichiometry control problems, carbon incorporation and unwanted side reactions. Several groups of researchers have investigated alternative sources of both the group III and group V elements. A review of these new organometallic precursors is presented in this paper. However, because group III and group V elements form Lewis acid-base adducts in the CVD reactor, we have investigated the attractive idea of using this class of compounds as single starting material. Several adducts have been successfully used for epitaxial growth of GaAs. Moreover, to avoid loss of stoichiometry due to dissociation of the adduct, the ability of organometallic molecules which feature a covalent bond between the group III and group V elements has also been investigated. These covalent compounds are probably formed in the MOCVD reactor using alkyl group V compounds containing acidic hydrogen R_3-nMH_n (M equals As, P; n equals 1.2). These new precursors are also briefly reviewed.

The structure and electronic and optical properties of SnSe films prepared by flash evaporation and hot wall epitaxy techniques onto different substrates have been presented. It has been observed that films deposited on glass and mica substrates are polycrystalline in nature, while the films grown on KCl substrates are found to be epitaxial. Grain size as large as 4 micrometers has been obtained for films prepared by the HWE technique. The electrical conductivity and carrier mobility of HWE grown SnSe film are comparatively higher than those obtained by conventional evaporation techniques. The absorption edge of SnSe films is due to an allowed direct transition of energy of about 1.22 eV. An attempt has been made to fabricate and characterize the FTO-SnSe heterojunction.

This article mainly deals with the exact origin of 0.15 - 0.20 eV defect level in CdTe--a controversial issue under debate for more than three decades--and some investigations of deep and interface levels in polycrystalline n-CdTe. The first issue still stands unresolved amidst conflicting views from various workers, thereby leaving it surrounded by an air of uncertainty. The results of a study of deep and interface states in Mo-polycrystalline n-Schottky barriers using a deep level spectrometer DLS-82E (Hungary), both in differential DLTS and level profile mode, are also presented. Three deep levels with activation energies of 0.2, 0.43 and 0.65 eV and capture cross-section of the order of 10^-18 cm² detected in the bulk of layers are discussed.

All II-VI semiconductors with melting temperatures well above 1000 degree(s)C and with appreciable congruent vaporization well below their melting temperatures leave little scope for any growth technique except for the slow but efficient vaporphase growth method. Theoretical flaw in diffusion models of vapor phase growth was corrected by Factor and Garrett by incorporating the flow velocity term which otherwise would lead to segregation of constituents. An additional degree of freedom arising from the presence of two components was well utilized to finely control the stoichiometry in binaries. In mixed II-VI systems the components are either three or four, depending on whether the system is a ternary or a quaternary. The added degrees of freedom make it very difficult to control stoichiometry. However, Igaki et al. demonstrated the feasibility of control of stoichiometry in CdS_xSe_1-x. In this paper, a self-sealing vaporphase growth technique used for both ternary and quaternary system is described. The systems studied are CdS_xSe_1-x, (ZnSe)_x(CdTe)_1-x and (ZnTe)_x(CdSe)_1-x. Results on growth mechanism, miscibility, structure, band gap variation, conductivity type variation with 'x' and transport properties are presented in a comparative way and discussed. CdS_xSe_1-x system in the entire 'X' has the same crystal structure and type of conductivity. The second system has the same zincblend structure but the type of conductivity is very sensitive to thermal treatment. In the last system both structure and types of conductivity are different. The discontinuities in properties associated with this divergent end compound are presented and discussed. Among the physical properties/parameters studied crystal structure, bandgap and nature of conductivity are tailorable, and magnitudes of conductivity and dielectric properties are very difficult to control in the crystals grown by this vapor phase method.

A quantum well injection transit time (QWITT) diode has been proposed recently to improve the performance of quantum well devices incorporating the effect of transit time of carriers. Earlier, transit time devices such as IMPATT, BARITT, DOVATT, TRAPATT, TUNETT show different types of performances with certain limitations. QWITT is a low noise device applicable to the sub-millimeter frequency range. Large signal simulations show that a QWITT device may be capable of producing approximately +5 dBm power at 200 GHz.

The effects of extrinsic factors on the reliability and performance of semiconductor devices are significant, especially when these devices are used for critical applications. The major extrinsic factors affecting the performance of devices are electrical overstress (EOS), electrostatic discharge (ESD) and radiation. The failure modes/mechanisms associated with EOS and ESD vary with technologies, device density as well as the failure location. The commonly observed failure modes are open circuit, short circuit, excessive leakage current, reduction in threshold voltage, snap back breakdown, etc., and the failure mechanisms are metallization melting and spiking due to electrothermomigration and Joule heating, junction fusing by second breakdown, dielectric breakdown, etc. In most cases the failures can be catastrophic, whereas latent failures are also possible due to EOS/ESD. Such latent failures are very vulnerable and can lead devices to fail during usage. Here an overview on the study on the physics of failures including that of latent effects induced by EOS and ESD is presented.

The solar control properties of vacuum deposited Cu₂Se thin films were investigated and the results are reported. The optical transmittance and near normal specular reflectance characteristics of these films showed that they exhibit suitable solar control characteristics for application as solar control coatings.

The aging (increase in film resistance with time) of CdSe thin films in oxygen and air at various substrate temperatures are reported. The films aged at low temperatures attained saturation in film resistance faster than those aged at higher substrate temperatures. This may be explained by considering the difference in the oxygen chemisorption rates in various films.

The electrical properties of In_xSb_1-x(0 < x < 1) alloy films deposited on glass substrate in a vacuum of 10^-5 torr have been studied. It is observed that films with composition around x equals 0.6 show minimum resistivity, maximum carrier mobility and more order in structure. The charge carriers appear to be holes for all compositions. The thermoelectric power of InSb films increase initially and shows maxima around x equals 0.2, beyond which a decrease is found with the increase in In content.

Tin selenide films have been prepared by flash evaporation technique onto glass substrates kept at different temperatures. An appreciable increase in grain size has been observed with increase in substrate temperature, grain size as large as 0.43 m has been obtained for the films deposited at 523 K. Observations reveal that SnSe films appear to be p-type and poly-crystalline in nature. The activation energy shows an abrupt increase beyond substrate temperature of 523 K, indicating poor crystallinity and short range order. The mobility and carrier concentration of SnSe films increases with increase in temperature.

Thin films of different thicknesses of the ternary semiconductor Se(10)Sb(10)Te(80) have been vacuum deposited at a very fast rate onto cleaned glass substrates at room temperature in a vacuum of 5 X 10^-5 torr. I - V characteristics of the thin films have been determined at room temperature and at a higher temperature. Also, the resistance of the different thickness films has been measured as a function of temperature both during heating and cooling. X-ray diffractograms of the films have been taken both before heating the films and after the heating (during the process of measurement). It is found that the I - V characteristics of the films are near-linear both at room temperature and at the higher temperature, indicating that these films cannot be used for making switching devices. The resistance of thin films decreases with the increase in temperature, indicating that the films are semiconducting. The resistances of the films during heating and cooling at a given temperature are slightly different, showing that some rearrangement of the microstructure of the films has taken place due to the heating. The thickness dependence of the resistance of the films (at a given temperature) does not apparently follow the dependence as expected from the size effect theories even though there is an increase of resistance for smaller thickness films. The x-ray diffractograms of the films before and after heating also show that even though there is no major rearrangement in the films, there is a change in the number of microcrystallites preferring a particular orientation.

Complex ac impedance measurements on Poly metallo phthalocyanines before heat treatment (I[MPc]_n(M equals Cu, Ni)) have been performed and the data analyzed using the Havriliak-Negami dispersion relation for polymers. The parameters so obtained are reported. Heat treated polymers (II[MPc]_n (M equals Cu, Ni)) show an increase in dc electrical conductivity, (sigma) , by several orders of magnitude. The temperature dependence of (sigma) is in accordance with that expected for variable range hopping of carriers in 3 dimensions (VRH 3D) for II[CuPc]_n and that expected for VRH of carriers in 2D (VRH 2D) for II[NiPc]_n. The significant deviation from linearity of the log((sigma) (root)T) vs T^-1/4 plot at low temperatures can be accounted for by the model proposed by Sheng which is based on electron transfer across insulating gaps in conducting pathways by fluctuation induced tunneling. Hall mobility measurements of II[CuPc]_n show that the carriers are holes and the Hall constant was found to be 6 X 10^-4 (Omega) m/T at RT.

Ultrathin tunnel oxides (SiO_x) were grown on silicon, pretreated with 5% hydrofluoric acid, using high pressure, low temperature oxidation. These oxides were characterized using variable illumination current-voltage (V_oc - J_sc) measurements on semi-transparent metal gate MIS diodes. The open circuit voltage (V_oc), short circuit current (J_sc), ideality factor (n) and reverse saturation current (J_o) are studied as a function of oxidation time. The interface state density D_its for the HF treated sample was found to decrease from 2 X 10¹² cm^-2eV^-1 to 9.21 X 10¹¹ cm^-2eV^-1. Highly reproducible, good quality ultrathin oxides were obtained by pre-treatment of the wafer in hydrofluoric acid.

Dc and ac conductivity studies were made on a-CuInTe₂ thin films deposited onto substrates held at liquid nitrogen temperatures. The dc results may be understood in terms of three modes of current paths, viz., hopping of carriers near the valence band tail, near an acceptor induced defect state and near the Fermi level at appropriate temperature ranges. A reasonable fit to the ac loss data could be made using the extended pair approximation due to Summerfield. Dc conductivity measurements were made using a two probe gap cell configuration. Thick Cu/In strips with well-defined parallel edges were deposited on the sample for electrical contacts. Film thicknesses ranged from 1500 to 6000 A. One electrode of the film was connected to a constant dc voltage source, and the other electrode was grounded through a Keithley 610 electrometer. The applied voltage was 5 V (corresponding to a field of 5 Vcm^-1), which was well within the ohmic region of the film's I - V characteristics in the temperature region scanned. Cooling and warming up rates used in the measurements were of the order of 0.3 deg min^-1. The current noise was below 10^-15 A and the drift of the electrometer during the experiment was checked periodically. As deposited, all the films were p-type in nature as envisaged by the hot probe method.

Amorphous CuInTe thin films were prepared by the flash evaporation of CuInTe powder onto substrates held at liquid nitrogen temperature. The amorphous nature of the films was confirmed by TEM studies. Compositional analysis was carried out using x-ray photoelectron spectroscopy and cyclic voltammetry. Amorphous to crystalline studies made on the films showed them to crystallize at about a temperature of 145 degree(s)C. Optical absorption studies yielded an optical gap of 1.30 +/- 0.01 eV.

Silicon nitride and silicon oxynitride films were grown using silane and locally available nitrogen and ammonia by PECVD technique. The results of structural characterization by IR absorption and ellipsometry studies are reported. MNS test structures were fabricated and a surface state density of approximately 10¹¹ cm^-2 was obtained from C-V measurements. Study on the probable current condition mechanism in these films showed results consistent with Frenkel-Poole mechanism.

A model for the oxygen-related donors in Cz-silicon with emphasis on their generation, reduction, and subsequent behavior in the transition region has been developed. A modified SiO_x model is presented to account for the new oxygen donors. A schematic diagram of the formation of donors and related defects so developed in silicon from the un-annealed to the annealed stage is also given.

Mg-Zn₃P₂ structures are examined as solar energy converter and broad-range photodetector. A distinct photodichroism observed for junctions prepared on oriented single crystal is applied in light polarization step indicator.

Metal-Oxide-Semiconductor (MOS) diodes with approximately equals 300 angstroms thick, thermally grown silicide dioxide (SiO₂) films were subjected to time-dependent oxide breakdown (TDOB) by applying a constant voltage (electrical stress). The breakdown of the oxide was achieved under the accumulation region of the substrate. After the breakdown of the oxide, V - I characteristics of the devices were measured. The observed characteristics are similar to the characteristics of a solid-state rectifier in nature. This behavior of the MOS samples has been qualitatively explained in this paper, on the basis of the nucleation and growth of the crystalline silicon from the oxide layers during the oxide breakdown process.

CuGa_0.5In_0.5Se₂ thin films grown on Corning 7059 glass substrates at T_x equals 598 - 648 K in a vacuum better than 2 X 10^-6 torr were nearly stoichiometric and polycrystalline. Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. The temperature dependence of the electrical conductivity suggests that above 400 K the conduction mechanism is intrinsic, whereas extrinsic/impurity conduction dominates in the range 303 - 400 K. The optical absorption studies revealed a fundamental energy gap of 1.29 eV.

A-SiC:H films were prepared by magnetron sputtering of silicon in an atmosphere of argon, hydrogen and acetylene gas on c-Si and glass substrates maintained at a temperature of 250 degree(s)C. It was indicated from the FTIR spectroscopy that the vibrational modes of SiC- and SiHm-shifted to higher energies due to the incorporation of carbon in a-Si:H network. The decrease of dark and photo conductivity with the carbon content was attributed to the additional defects produced by alloying of carbon in the a-Si:H.

Polycrystalline Zn_xCd_1-xS/CuGaSe₂ thin film heterojunction solar cells were prepared by laser evaporating CuGaSe₂ onto sprayed Zn_xCd_1-xS films. The reasons for the low efficiency of the cells were discussed in view of the poor performance of the device for x > 0.6. The photovoltaic properties of the cells were studies using illuminated I - V characteristics. A maximum efficiency of 4.9% was obtained on the cells.

The scanning electron microscope has been widely recognized as one of the most important surface analytical instruments by providing a higher resolution morphology and composition of surfaces. The instrument also provides a unique feature of assessing the electrical operation of the complex devices using the electron beam induced current and voltage contrast modes of operation.

Grain boundaries play an important role in the conductance of polycrystalline semiconductors. In the present work we have studies for the first time the effect of doping concentration on the grain boundary barrier height for different interface state density for polysilicon, considering that the grain boundary has certain finite width.

Experiments have been performed on Ni/n-Si(111) Schottky diodes fabricated by the thermal vacuum deposition of nickel on n/n⁺ Si epitaxial wafers at approximately 10^-5 torr pressure. (I - V) and (C - V) characteristics have been measured at different frequencies in the range 10 KHz-1 MHz. Hydrogenation effects on the diode characteristics have been reported from (I - V) and (C - V) studies. It has been found that hydrogen lowers the work function of nickel and also generates the interfacial traps at the Si- SiO₂ interface. These results are found in agreement with the results based on transient capacitance response and (C - V) studies. Slight passivation of deep donor states responding the low frequency test signal has also been observed after hydrogenating the diode. Interface states parameters have been extracted from (C - V) characteristics using the metal-interfacial layer semiconductor (MIS) structure model.

The electrical conductivity, Hall coefficient and Thermoelectric power of well-sintered pellets of semiconducting Ga_xIn_1-xSb solid solutions (x equals 0, 0.2, 0.5, 0.6, 0.8 and 1) were determined in the temperature range 300 - 425 K. Magnetic studies have also been conducted on powder samples over a similar temperature range. The variation of dc electrical conductivity with temperature was found to be in accordance with the Seto's model. Solid solutions with x equals 0.5 and 0.6 have been found to show the Hall effect sign anomaly. Various kinds of scattering mechanisms under different temperature ranges have been observed in different solid solutions. The magnetic susceptibility values of all solid solutions were found to be negative and diamagnetic throughout the temperature range investigated. The Van Vleck paramagnetic susceptibilities have been calculated for GaSb and InSb in the temperature range 300 - 450 K with the help of the bond-orbital model.

Amorphous semiconductors in the system Ge_xS_1-x are an interesting class of materials which exhibit quite different short range order in crystalline and amorphous state and form stoichiometric compositions like GeS, GeS₂ Ge₂S₃. Lead sulphide has been found to form stable glasses with GeS₂ in the presence of GeS. The exhibit photoconductivity of ambiopolar type1 Nature of electronic transport in these semiconductors is not well understood. It is of interest to study their electronic properties ard determine density of defect states in the bard gap. In this communication we have studied the a.c. conductivity of bulk amorphous (PbS)_x(Ges)_{0 7-x} (Ges₂) and Ge₄₂S₅₈.

Calculations of the variation of the photon field in the surface region of Si is presented which plays a significant role during photoemission. Ab initio calculations of vector potential gives information about the nature of the photocurrent emitted from the surface of Si. The scattering cross-section from the surface of Si is also calculated whose dependents on the photon energy is shown.

The effect of surface recombination and modulated frequency on the intrinsic parameters of an ion implanted GaAs optical field effect transistor have been analyzed. The study reveals that the gate-source capacitance increases with gate-source voltage, first slowly, and then sharply under normally OFF condition with the increase of modulated frequency. However, the surface recombination reduces these effects depending upon the trap center density. These variations are small in a normally ON device. Also, the drain-source resistance is found to increase with the increase of modulating frequency, but it reduces with the reduction of trap- center density at a fixed flux density and drain-source voltage.

P - Sm₂S₃ films were electrodeposited from aqueous 0.05 M Sm₂O₃ - 0.05 M Na₂S₂O₃ - 0.25 M tartaric acid onto a variety of substrates. Optical absorption, x-ray diffraction, and (photo) electrochemical studies were carried out. I - V, C - V characteristics were studied.

Diffusion of phosphorus in polycrystalline silicon is carried out from POC1₃ source at 1000 degree(s)C for 1 hour. The diffusion profiles were obtained and were analyzed to get diffusivity as a function of concentration.

In this paper, we report on the chemical deposition of a large area (approximately equals 50 cm²) of Ag₂S films from an acidic medium using thioacetamide as a sulpher source. The effect of deposition temperature from 8 to 55 degree(s)C was studied. The electrical resistivity microstructure and XRD of the films have studied. Photoelectrochemical cells showed that the films are n type and photoactive in nature.

In any laboratory to carry out temperature dependent studies a reliable temperature controller is required. Temperature controi! lers may be of analog or digital type. The main drawbacks of the analog controllers are (i) limited controllability or automation and (ii) hardware limitations in implementing mathematical computations. Digital controllers are flexible as the implementabtion of the control schemes are carried out by software only. Hence, the hardware restrictions of analog controllers can be completely eliminatec Automatic control of process parameters can be accomplished by different contrOl schemes or control algorithms such as Proportional (P), Proportional + Integral (P1), Proportinal + Differential (PD), Proportional + Integral + Differential (PID) algorithms. All the controllers produce a control output by operating on the error signal or a time series of error signals. Most process loops where the plant transfer function has not been completely defined are controlled by PID control algorithms. PID control schems can be implemented in different forms such as (i) positional or whole value form (ii) incremental or velocity form. Of the two, velocity form of PID algorithm provides certain advantages over the other. In this paper, a modified velocity form PID algorithm developed in our laboratory to control the process namely temperature is described.

The method of optical waveguide fabrication by ion-exchange has various advantages such as low loss, ease of fabrication, low material cost, etc. In the present paper, a package developed for the simulation of the ion-exchange process has been discussed. This simulator helps in simulating the required profile and consequent mode structure by manipulating the fabrication parameters. The complete package has been written with user orientation.

Due to the involvement of shorter time and energy consumption, rapid thermal processing (RTP) technique finds its success in Semiconductor processing. The Al-Si ohmic contact has been formed and the effect of alloying temperatures between 450 degree(s)C and 550 degree(s)C on this contact has been studied. The nature of the contact is probed well by positron lifetime spectroscopy (PLTS). The measurements are supported by I - V characterization and SEM.

Thin films of pure and silver doped zinc telluride were deposited on well-cleaned Corning glass substrates maintained at temperatures in the range 303 - 598 K by the vacuum evaporation method. The electrical conductivity of the pure films decreased from 1.1 X 10^-5 to 4.4 X 10^-6 ohm^-1 cm^-1 with the deposition temperature. The activation energy in the high temperature region was 0.33 eV, while at low temperatures it was 0.06 eV above the valence band. In the Ag doped films, the conductivity increased one order of magnitude. The optical band gap reduced from 2.23 eV to 2.18 eV with the Ag doping content.

Thermal oxides on polycrystalline GaAs thin films are grown at 10^-04 Torr and 600 K. The oxide layers are studied by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS). The core level spectra of Ga and As are obtained at different takes of angles. The oxide content of the films was found to increase with a decrease in the take of angle. The As₂O₃ content was found to be less than that of Ga₂O₃.

While the importance of the property of 'polarizability' in the studies of the structures of simple, synthetic and biomolecules is established clearly, an attempt is made in the present paper to make use of the optical polarizability and its components along axial and equitorial directions and subsequently the susceptibility to correlate with the phase transitions of semiconductors of the II - VI type. The semiconductors studied so far in the present investigations are (alpha) and (beta) phases of ZnS, ZnSe, ZnTe, and (alpha) and (beta) phases of Cds and HgS.

Transparent conducting thin films of tin oxide, doped with antimony were prepared by spray pyrolytic process under controlled conditions on borosilicate glass substrates, using pentahydrate tin chloride (SnCl₄ .5H₂0) as the starting material. Variations in parameters such as, the substrate temperature T5 and post-deposition annealing temperature TA were studied. Electrical and optical properties and x-ray diffraction studies of these films were studied to characterize these films.

CuGaS₂ thin films have been prepared by the spray pyrolysis method. These films have been found to be single phase and chalcopyrite in structure. The lattice parameters a and c as well as the optical band gap of these films have been determined. The films exhibited p-type conductivity.

Microwave device characteristics of 35 GHz InP DDR have been obtained through accurate numerical simulation, and those are compared with the properties of Si and GaAs DDRs. The results indicate InP as a promising material for fabrication of IMPATT devices.

We have calculated the mobility of 1s-excitons confined in a GaAs/AlGaAs quantum well limited by different scattering mechanisms over a temperature range from 10 K to 150 K for different well-widths.

Electrical resistivity of Cd_0.3Ni_{0.7 + x}Mn_xFe_{2 - 2x}O₄ ferrites has been measured in the temperature range from 300 K to 1000 K. Three distinct regions have been observed in log (rho) Vs 10³/T curves for all the samples. This is explained on the basis of the hopping mechanism. The conduction in the first region is due to impurity charge carriers. In the second and third regions it is influenced by the order-disorder hopping mechanism. The variation of resistivity with Mn concentration shows an increase in resistivity up to x equals 0.10 and decreases with further increase of x. The increase in resistivity is due to stable bond formation of Fe² + Mn⁺³ at B site which hinders the Verway mechanism. The decrease in resistivity is attributed to the formation of Ni³⁺, Mn³⁺ clusters and Mn₃O₄ + Mn₂O₃ impurity phases. Additional trapping due to local Jahn-Teller distortion around Mn³ and Mn⁴ also plays an important role in these materials.

Electrical resistivity of the ferrites Cu_{1 + x}Ti_xFe_{2 - 2x}O₄ (x equals 0 to 0.5 insteps 0.05) has been measured in the temperature region 300 K to 700 K. It is seen that the plots of log (Rho) Vs 1/T exhibit a linear relationship throughout the temperature range. The conduction mechanism in these ferrites is explained on the basis of the hopping mechanism. The conduction in the low-temperature region (< 370 K) is due to impurities defects and interstitials, etc. In the high-temperature region (i.e., > 400 K), it is mainly due to hopping of small polarons. A sharp deviation from linearity is observed around 520 K which is related to the transition temperature close to tetragonal to cubic transformation. The compositional variation of resistivity increases slowly at lower content of Ti < 0.2 and monotonously for higher content > 0.3. The slight decrease in resistivity at x equals 0.2 is related to structural change from tetragonal to cubic. The variation of resistivity with Ti_x is attributed to the hindering of the mechanism for x < 0.2 and for x > 0.3 to impurities, in homogenous distribution of cations in the spinel.

Some basic optical processes in quantum well structures are described and some photonic devices utilizing the processes are discussed. The operation of the devices depend on the interaction between particles and the scatterers. The scattering mechanisms are mentioned and the role of the processes on absorption, lifetime, line width of emission and mobility are indicated.

Powders prepared from vapor phase grown single crystals of (ZnTe)_x(CdSe)_1-x ε in the entire range of x were subjected to differential thermal and thermo gravimetric studies in the temperature range 300 - 1110 K in air atmosphere. The general decrease observed in differential temperature is attributed to vaporization of constituents as II - VI compounds and their alloys evaporate rapidly well below their melting points. Some exothermic peaks were also observed at different temperatures. In samples of all compositions, a very sharp peak around 920 K was observed. All the exothermic peaks in DTA curves showed corresponding effects in TG cures. This shown that the peaks are not associated with phase changes reported in similar other II - VI quaternary namely (ZnSe)_x(CdTe)_1-x crystals. The heats of reaction did not show any regular variation with composition. The TG peaks are attributed to stable oxidation states of Zn/Cd whereas the dips could be due to the formation of unstable oxides of chalcogens. The rates of reaction/evaporation showed that the vaporization phenomenon dominates over the oxidation processes in samples with <EQ 0.5. This is in conformity with the observed lower growth rates of crystals with x < 0.5.

The dielectric constant ((Epsilon) ) and the dielectric loss factor (tan (delta) ) of vapor phase grown single crystals of (ZnTe)_x(CdSe)_1-x in the entire range of x have been measured in the frequency range 10 KHz - 1 MHz and in the temperature range 160 - 365 K using Ag contacts. Crystals of different compositions exhibited different frequency dependencies. In crystals with x equals 0.0 and 0.2, tan (delta) passes through a maximum. However, in crystals with x equals 0.4, 0.5 and 0.6, tan (delta) exhibits a minimum. In samples with x equals 0.8 and 1.0, tan (delta) decreases monotonically with frequency. This complex behavior of loss factor is explained by assuming an inclusion of two Schottky capacitors in series arising due to the metal (Ag) - semiconductor contacts and a frequency insensitive series resistor due to lead resistance and invoking a plasma effect due to free carrier dispersion. The inclusion of a double capacitor in the circuit was further confirmed by I - V studies on all the samples using Ag, Pb and In contacts. At 400 KHz (Epsilon) and tan (delta) increased monotonically with temperature. In samples with x equals 0.4, increased and tan (delta) decreased with temperature. For x equals 0.5, tan (delta) passed through a minimum around room temperature. For other compositions, no regular variation of (Epsilon) and tan (delta) is observed. This complex behavior could be due to the dielectric contribution arising due to the piezoelectric nature of the constituent compounds of the present system.

Band gaps of vapor phase grown (ZnTe)_x(CdSe)_1-x single crystals in the entire range of composition x are obtained by photoconductivity spectral response and diffuse reflectance spectral analysis. The band gap varies nonlinearly with composition and passes through a minimum around x equals 0.3. A least-square fitting of energy gap values to a quadratic equation gives a bowing parameter of 0.724 eV. The bowing parameter calculated using Hill and Richardson's equation is also found to be 0.724. However, Chandrasekharam et al. reported a value of 1.088 eV for (ZnSe)_x(CdTe)_1-x single crystals. Pseudopotential and dielectric models are generally used to estimate the bowing parameter of similar miscible crystal structures. However, the systems involved in the present study are divergent with wurtzite and zinc blend structures. It is shown that the pseudopotential model fails to account for the observed bowing due to the presence of structural transition in the present system.

CuInS₂, a promising material for tandem solar cell realization, is doped with Mn, a probing dopant for crystal fields and a creator of fluorescent levels in several crystals. 0.7, 1.2 and 1.9 at % of Mn doped p-CuInS₂films were prepared by spray pyrolysis. XRD studies confirmed the chalcopyrite structure with C equals 11.02 and a equals 5.51 A. The direct bandgap obtained from transmission spectra was found to increase with Mn content in the range 1.38 - 1.56 eV. Hall effect studies in the temperature range 190 - 273 K showed a decrease of hole concentration with doping indicating the creation of donor levels by Mn.

The effect of carrier diffusion on the breakdown characteristics of GaAs and InP avalanche diodes has been investigated using experimentally reported diffusion constants and ionization rates of electron and holes in semiconductors. The results show that diffusion causes some change in current distribution and electric field profile in the depletion layer of both GaAs and InP diodes. The avalanche zone is widened and the breakdown voltage decreases due to diffusion.

No abstract available.

The numerous interdependent variables existing in the reactive ion etch process complicates the understanding of the etch mechanisms operating in the plasma processing. The knowledge of the exact mechanisms will, however, be useful for developing an etch process with improved etch rate, etch profile, selectivity, uniformity, etc. The results of a detailed study on the etch behavior of Si, SiO₂, and Si₃ N₄ in fluorine and chlorine containing gas plasmas are reported in this paper, to arrive at some of the possible mechanisms operating in the reactive ion etch process.

The photo-ferroelectrics are a special class of ferroelectrics to be used for optical processing of information, memory and display in integrated optoelectronics. They have better device potentials for electro-optical switching, modulation and wave guiding. Interfacing a ferroelectric directly on semiconductor material modifies the basic electrical properties of the semiconductor and it has been possible to construct several new types of field effect transistors. These are nonvolatile memory devices that can be incorporated in an integrated circuit. The ferroelectric thin film polarization is utilized to control the surface conductivity of the semiconductor substrate for its memory function.

Reactive ion etch induced damage in silicon have been studied in terms of its electrical characteristics. Samples were plasma etched in the commonly used gases SF₆, CF₄ and O₂. The extent of damage was determined by evaluating the Schottky barrier diodes fabricated on the etched silicon surfaces. The behavior of these defects was also studied. These results were further compared with damages induced by plasmas of chemically active (N₂) and chemically inactive (Ar) gases.

Subthreshold characteristics of a thin-film Silicon On Insulator (SOI) MOSFET are analyzed using a charge sheet model, taking into consideration the charge coupling effects between the front and back channels. The effects of back gate bias and the interface trap density are studied using the analytical expressions derived in this approach, and it is shown that the near ideal subthreshold slopes can be realized when the back gate is connected to the front gate. The results also show that when the back channel is biased to accumulation the subthreshold slopes become worst.

Aluminum films (99.999%) were deposited onto p-type <100< silicon wafers. The samples were implanted at room temperature with 1 X 10¹⁷, 3 X 10¹⁷ and 5 X 10¹⁷ O₂^PLU - cm^-2 at 30 keV. XPS spectra was recorded for Al_2p3/2 and Si_2p lines at various depths. XPS studies confirmed the formation of Al₂O₃ at all doses and SiO₂ at 5 X 10¹⁷ O₂⁺ - cm^-2.

Pd/Si devices both on n/n⁺ and p/p⁺ substrates have been placed in hydrogen atmosphere with the intention of introducing atomic hydrogen in silicon at room temperature. The palladium films on the top of the silicon substrates absorbs hydrogen to form PdH_x, and the hydrogen is subsequently released into silicon, which causes the passivation effect. The shallow dopants, both in n and p silicon substrates, are passivated to the extent of 30% and 50% respectively on hydrogenation. Frequency dispersion of capacitance shows the hydrogen passivation of deep states.

We have observed for the first time in an n-p-n bipolar transistor that if one of the junctions is forward biased and the other is left unbiased, then a voltage is developed across the unbiased junction. This effect is similar to the well-known photovoltaic effect in generation of the voltage across an unbiased p-n junction but differs in the method of creation of the excess minority carrier concentration which is responsible for the generation of the voltage. We therefore refer it to as the electrovoltaic effect. In a p-n-p structure the electrovoltaic effect is due to holes. Electrovoltaic effect can have many applications alone or in combination with another effect or phenomenon. We have designed a new solar cell which is based on a combination of electrovoltaic and photovoltaic effects. This solar cell is a four-terminal device and its structure is essentially an integration of n⁺-p-n⁺ and n⁺- p-p⁺ structures into a single structure. The output power of this cell can be controlled by manipulating the contribution of the electrovoltaic effect vis-a-vis the photovoltaic effect in delivering the power to the load.

The electrical and optical properties of sprayed indium tin oxide (ITO) films have been reported as a function of substrate temperature and tin concentration. Highly conducting (approximately equals 1 X 10⁴ mho/cm) and transparent (approximately equals 90% in the visible region) ITO films were obtained when the substrate temperature is 420 degree(s)C with 5% by weight of tin. The refractive index of the films varies from 1.9 to 2.2.

Amorphous chalcogenide semiconductors are generally ptype semiconductors and added impurities do not alter their conduction type. For development and characterisation of new amorphous semiconducting materials for their diverse technical applications, it is important that their electronic properties and microstructures should be well understood. Further, it should be possible to make them n/p type in acontrolled way. In this context Ge Ml. (M=S, Se, Te) glasses are unique amorphous semiconductors which exhibit p—n transition in their electronic conduction wnen modified with large concentration of Bi impurity (11 at%, 7 at% and 3.5 at% Bi in Ge—S, Ge—Se and Ge—Te respectively (1,2,3). We have recently been investigating this new class of materials to understand their unique properties (1,4,5). In this talk I would present a brief account of some our recent - findings on the semiconductors in the system Ge-S-Bi. Among the amorphous Ge-M, (M=S, Se, Te) semiconductors, the system GeXS1.X occupies a unique position. In the qlassy form these alloys have short range order which is dependent upon value of x and is quite different from that in the corresponding crystalline form (6) Further, this is the only system among the chalcogenide glasses which exhibits ESR signal under ambient conditions.

A series of bulk amorphous samples of Ge₁₅Se_{85 - x}Bi_x (x equals 0, 2, 4, 6, 8, 10) were prepared by the rapid quenching technique. Electrical transport properties such as dc conductivity and thermoelectric power were measured in the temperature range 80 - 350 K. An abrupt increase in the dc conductivity is observed due to the incorporation of Bi into the host Ge-Se system. The conduction sign changed from p to n at 8 < X < 10 as evidenced by the measurement of thermopower. The experimental data is explained in the light of existing theories.

The present paper reports the kinematic studies of glass transition in Se_{100 - x}Te_x glassy alloys using differential scanning calorimetry technique. From the heating rate dependence of glass transition temperature, the activation energy ((Delta) E_t) for the relaxation time controlling the structural enthalpy is calculated and its composition dependence is discussed in terms of the structure of the Se-Te glassy system.

The theory of cyclotron resonance (CR) lineshape of a two-dimensional electron gas (2 DEG) due to the electron-phonon interaction in the multiple-quantum-well structures (MQWS) is investigated. The contribution of the deformation potential acoustic and piezoelectric phonon scattering to the broadening of the cyclotron resonance spectra (CRLW) of such a system is calculated for GaAs/AlAs. The piezoelectric phonon scattering contribution to the linewidth is smaller as compared to the deformation potential acoustic phonon scattering but is significantly comparable. The magnetic field dependence of CRLW due to the deformation potential acoustic and piezoelectric phonons is B^1/2 and B^1/4, respectively, and the frequency shift equals 0 for both interactions in the elastic scattering approximation. Observed numerical values of the CRLW indicate that at low temperatures acoustic and piezoelectric phonons are dominant scatterers and interact strongly with 2D EG in MQWS where the impurity scattering is suppressed due to the modulation doping. Effect of screening on the scattering of electrons by statically screened longitudinal and transverse piezoelectric phonons in multiple-quantum-wells structures are also reported. Screened transverse phonons are found to play an important role in the scattering process. When the cyclotron orbit lies within the screening radius, CRLW is found to be large compared to the case when the cyclotron orbit lies outside the screening radius. Variation of the CRLW with respect to the magnetic field due to the combined scattering by longitudinal and transverse piezoelectric phonons is studied.

The anodization of GaAs in RF plasma may be strongly affected by thin metal layers, evaporated on top of the semiconductor before oxidation. Thin (approximately equals 2 nm) Al films first cause a retention followed by a dramatic increase of the oxidation rate. The energy spectrum of the interface is altered and the lattice contraction below the oxide is reduced. The oxidation is exceptionally fast beneath a Sm film. Other metals (Au, Cr) of similar or even smaller thickness prevent the successful oxidation or result in oxide of poor quality.

Artificial semiconductors compared of a periodic sequence of thin n- and p-doped layers, possibly with undoped (i-) layers in between, exhibit a number of unique features by which they differ from uniform bulk crystals as well as from semiconductors with a compositional superlattice. The properties which make them particularly appealing as a new kind of semiconductor are the tunability of carrier density, bandgap, two-dimensional subband structure, and recombination lifetime in combination with an enormous flexibility in tailoring. This tailoring includes the possibility of an additional periodic modulation of composition ('hetero n-i-p-i'). This can be used to reduce the disorder induced potential fluctuations by separating the free carriers from their parent impurity atoms, similar to the well-known 'modulation doping.' The possibility of varying conductivity, absorption coefficient, optical gain, and luminescence spectra by light or external electrical potentials implies new concepts for photodetectors, tunable light sources, and modulators. The long recombination lifetimes result in large, low-power nonlinearities of the optical absorption coefficient and the refractive index, including optical bistability. After a short review of the basic theory and fundamental properties of n-i-p-i structures we will demonstrate a number of properties which have turned out to be of particular interest for applications such as spectrally tunable electroluminescence, huge photoconductivity, strong electro-absorption and -refraction, and large optical non- linearities on homo- and hetero n-i-p-i systems. We also present results on a newly discovered peculiarity. N-i-p-i structures exhibit a giant ambipolar diffusion coefficient, which can exceed typical bulk values by more than two orders of magnitude and which allows for a control of the 'adjustable recombination lifetimes' down into the sub-ns regime. Finally we will present a new n-i-p-i-based concept of 'smart pixels' as fast optical logic gates at extremely low optical and electrical power dissipation.

Photostable hydrogenated amorphous-silicon films have been deposited by disilane decomposition in a quartz reactor 2 m in length and 5 in. in diameter. A deposition temperature of around 420 degree(s)C, pressure in the interval of 5 to 10 Torr, and gas holding time around 250 sec are the most appropriate parameters to deposit fairly good quality films having density states ranging from 10¹⁶ to 10¹⁷ cm^-3 eV^-1 and Urbach's tail from 70 meV to 100 meV.

Single-longitudinal mode lasers are key components in many optical communication systems. For single-mode operation commonly distributed feedback (DFB) lasers are used. Depending on the application, these devices have to fulfill different requirements in terms of optical output power, side-mode suppression, laser linewidth, bandwidth etc. On the other hand, it is well known that the DFB device characteristics can be severely deteriorated by spatial hole burning (SHB) effects. Therefore, it is the purpose of this article to review the effects of SHB on DFB laser characteristics and to discuss DFB structures with reduced SHB. The article is organized as follows: After a brief recovery on the theory and technology of DFB lasers, the effects of SHB will be described, followed by the presentation of some DFB structures with reduced SHB effects.

Photo-deep-level transient spectroscopy detection of a new level with thermal activation energy 0.22 eV of DX centers in silicon doped Al_xGa_1-xAs (x equals 0.26) is reported for the first time. The observation of this level directly proves the negative-U properties of DX centers and the existence of metastable state DX degree(s) which is also confirmed by the transient photoconductivity experiment.

Radiation damage due to B⁺ ion implantation in p-type HgCdTe has been found to create Hg interstitials giving rise to n-type conversion. The implantation energies were kept at 50 and 100 keV with a dose of 1 X 10¹³ cm^-2 each. The effect of implantation with ascending and descending orders of energies were found to be quite different from each other. Radiation enhanced diffusion is thought to be responsible for this anomaly.

This paper will review the theory of hopping conductivity and present some recent results for many-electron systems. In strongly disordered semiconductors at low temperatures the dominant transport process is electron hopping. This mechanism is relevant to conduction in amorphous semiconductors, impurity bands and some conducting polymers. A consistent theory of the process in a one-electron approximation is obtained in a rate equation approach and an approximate solution is given by the Extended Pair Approximation. Its results are consistent with large scale computer simulations and experiments. For the acceptor conductivity a universal scaling relationship can be inferred and this allows a strong classification of systems to be made. Impurity conduction in the presence of electron-electron interactions is studied by analytical and numerical techniques. At low temperatures there is a Coulomb gap in the density of states. Simulations of the percolation problem show the gross features of the behavior of the dc conductivity. It may be inferred that there is an effective one-electron mechanism in which the Coulomb gap has questionable importance.

We review the use of large strains both in the design an in the study of semiconductor structures and devices. Large hydrostatic pressure may be applied to samples and devices. This changes the band structure qualitatively without changing the crystal symmetry. We present some results obtained studying lasers by this technique, which reveal the loss mechanism dominating the thresholding current. A new high-pressure determination of the InGaAs/GaAs band offset ratio will be discussed. Axial strain may be applied to samples, or may be built into semiconductor epilayers by using thin layers of non-lattice matched compounds. This changes the crystal symmetry in ways that can benefit device performance. It also enables the structure to depart from the substrate lattice constant, which gives a new freedom to device design. Some recent advances in the InGaAlAs strained-layer system will be described.

Oxide layers on polycrystalline GaAs thin films were grown by thermal oxidation at 10^-4 torr. In depth profiles of the oxide layers were obtained by in situ Ar⁺ ion etching in x-ray photoelectron studies at different stages of sputter etching. These studies reveal a pile-up of elemental As at the interface between the GaAs film and the oxide layer. The observed compositional variation in the oxide layer at different depths is related to the selective sputtering of As O to As. Some of these results are presented.

Thin films play a crucial role in the present day science and technology due to their wide use in a large number of active and passive devices. Il—VI compound semiconductors have drawn considerable interest due to their potential applications in photovoltaic devices, photoresistors, heterojunction diodes, electrolumine scent layers and SAW devices. Thin films of these compounds are most promising for utilization in solar cells, particularly the cadmium chalcogenides which have received intensive attention, since their band gaps lie very close to the range of maximum theoreti cally attainable energy conversion efficiency. Cadmium telluride and zine selenide are another important material among the il-VI compound materials with a direct band gaps. Recently, ZnSe has emerged an impor tant material for use in non—linear optical devices as it posses large polarizability and non—linear co— efficient. A Brief Review of the work carried out on the Growth and Characterization of these Il—VI compound semiconductor viz. CdS and ZnSe has been presented here. The characteristic structural, electrical and Optical properties of thin films can be tailored by controlling the fabrication processes e.g. deposition rate, substrate temperature, selection and preparation of substrate, doping, ambient pressure)post deposition annealing e.g. thermal or laser annealing, passivation under high pressure of hydrogen.

It has been observed experimentally that the tunneling current across pn tunnel diodes decreases when a magnetic field is applied to it at liquid helium temperatures. Such a decrease is noticed both for longitudinal and transverse applications of magnetic fields relative to the direction of the current flow. Classically, tunneling of particles is regarded to propagate with the speed of light. Therefore, on the basis of the postulates of special theory of relativity tunneling of a potential barrier by particles should be independent of the state of motion of an observer relative to the tunneling system. In other words, the tunneling rate should remain unaffected of the motion of the observer. Therefore, to explain tunneling of particles in a crossed configuration of electric and magnetic fields, a suitable frame of reference for an observer can always be chosen so that the magnetic flux density observed from the new frame reduces to zero. The tunneling along the reduced electric field intensity may then be studied on established laws. The resultant electric field intensity in such a case becomes a function of the original magnetic flux density and it shows a steady decline with the increase in the magnitude of the latter. Therefore, a reduction in the tunneling probability and the tunneling current density is expected when the magnetic flux density normal to the current flow is increased. Finally, at a particular magnetic field intensity the tunneling current density drops to zero. It then turns out that the cyclotron frequency corresponding to this cut off magnetic field is proportional to the reciprocal of the tunneling time derived on the ideas of quantum measurement and observations. Therefore, by recording the normal magnetic flux density required to cut off the tunneling current across pn tunnel diodes immersed in a liquid helium bath, it may be possible to make an estimate of the tunneling time across a potential barrier. The working expression of the calculation of the tunneling time also follows independently of the relativistic treatment outlined above. The identity of results derived on the two approaches seems to justify the fact that the speed Of tunneling is really high enough so that the relativistic treatments may be applied to it as an approximation although tunneling may not propagate with the exact speed of light.

At present the international photovoltaic scenario is characterized by the following features: - during the. last decade the real commercial market has been steadily increasing, with a rate of about 20 % in recent years, and is by far larger than the government-supported market; - this commercial market is totally concentrated on "stand- alone" applications, where a competition by a public grid does not exist; - grid-connected large-scale photovoltaic power plants are no- where in the world competitive with conventional power plants; - the "power-sector" - medium and large-scale PV-installations - is dominated by solar cells made from crystalline silicon; - in the past the goals for efficiency development have been achieved, however, those for cost reduction of PV have always been too optimistic; - the cost reduction potential of c-Si is limited, probably to the range 1 to 2 US $ per peak Watt.

The lecture is introduced by a survey ofselJdffusion ofSi, which gives access to the nature of the most probable point deftcts. The major results on the diffusion of the main electron donors and acceptors are then summarized. The metallic impurities which can play a crucial role in the Silicon technology are also consit'kred. Their extraordinary fast dffusivity is tentatively explained. On the other hand, dfusion methods are also proposed to remove those metals (gettering). The latest experimental and simulation results of diffusion ofhydrogen and oxygen arefinally reported.

Among wide gap semiconducting compounds the alkaline earth suiphides are being exploited for device applications such as multi.- color thin-film electro.-luminescent, maieto.-optical and IR devices; dosimetry and high resolution imaging. Barium Sulphide (BaS), being one of the compounds of this class of semiconductors, has also been studied by various workers in view of its expected useful applications. The authors have been able to review the optical, electrical and defect structure properties of BaS. Activators and co-activators have been found to form luminescent centres in this material. Schottky disorder and vacancy migration has been observed to dominate in these crystals0 However, there remains a controversy with regard to the band structure o the material.

Vanadium doping of GaAs during LPE growth gives rise to an electron trap with an activation energy of 0.19 eV and capture cross section of 4 x 1Ocrn.

We present a model calculation o-f energy loss function for intralayer as well as interlayer interaction in modulation doped GaAs/AlGaiAs superlattice which consists of two GaAs layer at a distance d1 apart in a unit cell of length d. The intralayer interaction yields one acoustic and one optic plasmon modes while interlayer interaction gives only one. optic plasmon mode. The acoustic plasmon mode ceases to exist for very small values of wave vector and very large values of damping constant.

Our recently derived expressions for the electron-phonon (e-p) interaction relaxation rates have been appleid to the explanation of phonon conductivity of As-doped Ge beyond conductivity maximum. Due to the added role of dilatation deformation potential, Ed, in e-p relaxation rates we have been able to explain the phonon conductivity of As-doped Ge at higher temperatures for the first time.