Recently, AlGaN-based material and related devices have been investigated intensively because of their applications in ultraviolet solar-blind detectors, blue light-emitting diodes, UV laser diodes, and high-power-temperature devices. Due to intrinsic difficulty to grow high aluminum fraction material, achieving reasonable good quality of wafers is the key aspect to fabricate high performance solar-blind AlGaN-based detectors. Transmission spectra, XRD, and a two dimension transmission scanning system were employed to evaluate the properties of AlGaN-based material. Wet chemical etching process of n-type AlGaN in 20% aqueous KOH solutions was performed to reduce dry etching damages and the average leakage current. I-V characterization indicated that the average leakage current of the wet etching treated detectors was lower than that of the detectors without treatment by about one order of magnitude. Ti/Al/Ti/Au contact on n-type Al0.63Ga0.37N was optimized to get a low series resistance. 128×128 solar-blind AlGaN UV Focal Plane Arrays (FPAs) were fabricated and the performance were characterized. A CTIA (capacitive-transimpedance) readout circuit architecture has been proven to be well suited for AlGaN detectors arrays. The results show that 128×128 back-illuminated AlGaN PIN detector SNR is as high as 74 db at a speed of above 30 frames per second.

The emergence of solution-processed semiconductor quantum dot (QD)-light emitting diodes (LEDs) has recently offered a great prospect for developing low-cost, efficient, bright, and large-area colorful displays compatible with flexible substrates. The band-edge electroluminescence (EL) of colloidal QDs of cadmium compounds, exhibits size-tunable spectral emission (450-760nm) and narrow bandwidth (FWHM~15-30nm), allowing for the design and fabrication of color-saturated red, green and blue (RGB) QD-LEDs with simple device configurations and high spectral purities that outperform those of liquid crystal displays and organic light-emitting diodes. Additionally, high fluorescence quantum yield and photochemical stability can be achieved by engineering the nanocrystal surfaces with wide-bandgap shells, which favors the efficiency and stability of QD-LEDs. We report in this conference of our recently developed red, orange, yellow, green, blue and white quantum dot light-emitting diodes with high brightness, high efficiency, saturated color on both indium tin oxides (ITO) coated glass and on flexible PET substrate.

Cadmium sulfide (CdS)-sensitized solar cells have been investigated. Chemical bath deposition (CBD) based on an aqueous medium involving cadmium acetate, thiourea, ammonium acetate and ammonia was utilized to assemble CdS quantum dots (QDs) onto mesoporous TiO2 films for dye-sensitized solar cell (DSC) applications. Physical and chemical properties of the formed TiO2/CdS bilayers were analyzed using field emission scanning electron microscope (FE-SEM), Raman spectroscope, ultraviolet-visible light (UV-VIS) spectrometer and X-ray diffraction (XRD). An efficiency as high as 1.50% for the CdS Q dots-sensitized DSC was achieved using the present method. The results have demonstrated the potential applications of CBD CdS Q dots for sensitized solar cells.

Centrotherm photovoltaics AG has chosen Cu(In,Ga)Se₂ (CIGS) as material system for turnkey thin-film photovoltaic production lines because of its great potential concerning conversion efficiencies and economical production. Within CIGS thin-film technology, centrotherm overcomes several disadvantages of former technologies with a unique technology for the CIGS absorber layer formation. The new technology is based on sputter technology on one hand side and a rapid thermal process on the other side. Precursor metal layers are sputtered on large area and transformed to semiconducting CIGS in an ultra rapid thermal process step, which is performed under atmospheric pressure conditions. This leads to unreached short process time on the order of 1 minute and hence to a very high productivity, and prerequisites for real mass production on the GW scale.

With density functional theory (DFT), the structural and electronic properties of both neutral and different negatively charged (TiO₂)_n clusters with n=1-5 have been investigated. The HOMO-LUMO (highest occupied molecular orbital- lowest unoccupied molecular orbital) energy gaps as a function of the charge have been presented. The calculated results suggest that the least change of energy gap between (TiO₂)4 and (TiO₂)₄ ^2- happens, and the following is that of (TiO₂)₃ clusters. Distribution of extra electrons in (TiO₂)_n ^- and (TiO₂)_n ^2- has also been performed. The calculated results indicate that in both these two kinds of negative clusters, the excess charge is localized around the titanium with the lowest coordinated number. These theoretical results may be helpful for understanding the influence of electron transport on the small (TiO₂)_n clusters better.

First of all, the paper represents three main components, structure and working principle of solar energy photovoltaic system. It analyzes the principles and design elements of photovoltaic power generation system design, represents Steps and ideas of the design of the photovoltaic system, illustrates the acquiring informationand the method of software, hardware design at the same time. Finally, it discusss the applications of the photovoltaic technology.

The 3wt% aluminum-doped zinc oxide film (AZO) was sputtered on glass by radio frequency (RF) magnetron sputtering using ceramic target. What's more, sputtering was carried out at different substrate temperatures from 200°C to 350°C with normal deposition. The effect of deposition temperature on structural, optical and electrical properties of the AZO films was studied. It was found that the films become more uniform and compactness as the deposition temperature increased from 200°C to 300°C. Highly oriented AZO films in the (002) direction were observed in specimens deposited at 250°C and 300°C. In addition, It was showed that the average optical transmittance of specimens was about 85%. And there was an increase in electrical conductivity when deposition temperature increased from 200°C to 300°C. The lowest resistivity of 1.05×10^-3Ω•cm was obtained in specimen deposited at 300°C, which makes them available as transparent conductive electrodes in photonics devices including LCD flat panel displays and solar cells.

Silicon is a promising substrate for GaN growth due to its low cost, large size and potential applications in the integration of optoelectronic and microelectronic devices. However, a high lattice (~17%) and thermal (~56%) mismatch between Si substrate and GaN epilayer causes large tensile stress and leads to the formation of cracks when the GaN layer thickness is above 1.0 μm during the cooling down to room temperature. Therefore, the growth of high quality and crack-free GaN layers on silicon substrates is still a challenging issue. It has been widely reported that cracking problem can be mitigated by using techniques like low-temperature (LT) AlN interlayers, AlxGa1-xN transition layer, thin SixNy interlayers, AlN/GaN superlattices, etc. In this work, we used the LT-AlN interlayers for strain engineering during the growth of GaN layers by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) on Si(111) substrates. And we investigated the fluence of the thickness of LT-AlN interlayers, which is considered as one of the most important factors in reducing tensile stress and controlling density of micro-cracks in GaN layer. Optical microscopy, atomic force microscopy, X-ray diffraction and Raman spectrum were employed to characterize these samples of GaN epilayers. The results demonstrate that the crystal quality of GaN depends strongly on the thickness of the epilayers, and crack-free GaN layers with thickness exceeding 1.5 μm can be achieved by using LT-AlN interlayers with an optimized thickness.

We had demonstrated several novel methods to improve the luminescence efficiency of the GaN-based light emitting diodes (LEDs). The high-aspect-ratio GaN nanorods, formed by spun nano-spheres and inductively coupled plasma (ICP) etching, contributed to an enhancement in light output power and better light directionality. Nevertheless, the etching process would affect the electrical properties. We then attempt to rough the surface by synthesizing ZnO nanorods in liquid solution at room temperature. The LEDs with ZnO nanorods enjoyed high extraction efficiency and comparable electric performance than that without nanorods. At third part, we fabricate a high efficiency GaN-based LED by regrowth on SiO2 nanorod patterned sapphire substrate. It could improve the light extraction and internal efficiencies simultaneously.

Nanocrystalline TiO₂ porous electrodes were prepared by screen-printing method in order to efficiently control the fabrication process. TiO₂ viscous pastes were prepared from commercial TiO₂ nano powder using ethyl cellulose as a porosity controlling agent. A metal-free organic dye (indoline dye D102) was used as a sensitizer. TiO₂ porous electrodes with different thicknesses were investigated. The optical and physical properties of the TiO₂ films, dye adsorption behavior and performance of dye-sensitized solar cells (DSCs) were investigated systemically. The electronic and ionic processes in DSCs were analysized and discussed by electrochemical impedance spectroscopy (EIS). High conversion efficiencies over 8.00 % under illumination of simulated AM1.5 sunlight (60mW/cm²) were achieved.

Zinc oxide is a direct, wide bandgap semiconductor material with many promising properties for blue/UV optoelectronics, transparent electronics, spintronic devices and sensor applications. In this work, zinc oxide films were deposited by RF magnetron sputtering on different substrates. The images of field-emission SEM are used to analyse the structures of the samples, and some novel structures of the ZnO thin films grown on quartz glass and normal glass substrate are found. The x-ray diffraction is used to analyse the grain structure of these samples, it is shown that films grow mainly with the hexagonal c-axis perpendicular to the substrate surface.

In this paper we have studied AgxZn1-xO alloys by the method of the density functional theory with the generalized gradient approximation and the projector augmented wave pseudopotentials. In order to calculate the crystal structure of the AgxZn1-xO alloys with wurtzite structure, we adopt a 32-atom AgnZn16-nO16 supercell which allows the simulation of the silver composition x=0.0, 0.0625, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.875, and 1.0. The calculated results show that the formation energies and the calculated lattice constants of AgxZn1-xO increases by the x increasing. As a result, the doping of Ag becomes more difficult with the increment of Ag concentration. Furthermore,the solid solubility of Ag in wurtzite ZnO is small.

Except for the group-V dopants, Ag, as a group IB element, could also act as an acceptor in ZnO, if incorporated on substitutional Zn sites. In this paper, first-principles density-functional calculations have been performed to investigate various distributions of Ag in ZnO. The first-principles calculations were carried out using the density functional theory with the generalized gradient approximation (GGA) and the projector augmented wave (PAW) pseudopotentials. The supercell employed contained 32 atoms that corresponded to a 2×2×2 supercell of ZnO. The various distributions of Ag in ZnO have been calculated corresponding to each possible location. In conclusion, the calculation results show that the formation energies of Ag on the substitutional Zn site (Ag_Zn) and incorporation in the interstitial site (Ag_i) are smaller than that of Ag on the O site (Ag_O). When Ag_Zn and Ag_i coexist and are partitioned by an oxygen atom layer, the formation energy and the total energy is the smallest. As a result, Ag prefers to distribute discretely in Ag doped ZnO. It is also found that our results are in agreement with other experimental results.

The GaP layers grown on GaN layer by Metalo-organic chemical vapour deposition (MOCVD) were studied. The results show that the GaP layers are single crystals when the growth temperature varied from 350°C to 500°C. However, the crystal quality of GaP grown at low temperature is not good. Using a 40 nm GaP buffer layer grown at 400°C, the crystal quality of GaP grown at 680°C improves evidently. The p-type GaP layers with hole carrier concentration of 4.2×10¹⁸ cm^-3 were obtained by CP₂Mg doping.

In addition to dislocations, the wafer curvature can also affect the broadening of x-ray rocking curve (XRC) peaks and it may deteriorate the accuracy of the tilt and twist angle measurements. In this paper, the radial-distribution of curvature and the effects of wafer curvature on XRC of highly curved (the radius curvature of r less than 2.5 m) GaN layers were studied. Curvature-related effects both on symmetric geometry and on the (102) skew symmetric geometry were studied by the use of adjustable beam slits and 'antis.slit' placed before the sample and before the detector, respectively. The acceptable approaches to minimize the curvature-related effects in determination of a reliable tilt or twist angle were proposed. It is found that the curvature-related effects can be eliminated by the use of the methods we proposed. The dislocation densities obtained by high resolution x-ray diffraction (HRXRD) are fairly consistent with that obtained by cathodoluminescence (CL) and atomic force microscope (AFM).

The etching process has great influence on the performance of solar blind detector based on Al_xGa_1-xN epitaxial layers on sapphire substrate with high Al mole fraction grown by metal organic chemical vapor deposition (MOCVD) method. Traditional etching methods, including wet or reactive ion etching (RIE) are hard to achieve good result due to the high chemical-stability of AlGaN films with high Al mole fraction. In this paper, we studied on the inductively coupled plasma reactive ion etching (ICP-RIE) of high Al mole fraction Al_xGa_1-xN films (x>0.4) for fabricating high performance solar blind detectors. SiN was used as mask, and Cl2 and BCl3 were used as etching gas. Etching systems was selected from Oxford Inc. DC bias was controlled automatically. A 2.5:1 of selectivity on AlGaN and SiN was obtained with suitable flux and component of etching gas, RF power and ICP power. Etching velocity was adjusted mainly by RF power. The role of Ar, Cl₂, and BCl₃ in the etching process was also discussed.

In this study, a new cathode system of triazole (TAZ)/Cs2CO3/Al has been proposed. Obvious efficiency improvement and sharp enhanced electron injection were maintained in the devices with this new cathode. TAZ owns deep the highest occupied molecular orbital (HOMO) and wide band gap, so as to block the hole leakage effectively and confine the exciton in Alq₃ emissive layer. An abrupt lowering of the vacuum level was found in the mixture of TAZ and Cs₂CO₃, which indicated that the electron injection barrier from metal cathode into Alq₃ was greatly reduced. Our experimental proved that this new cathode may have a wide application in OLEDs emitting light with short wavelength.

Nanocrystalline TiO₂ electrodes have been coated with alumina by being immersed into the solutions of aluminum isopropoxide and aluminum acetylacetonate respectively. The current-voltage characteristics of the TiO₂ and TiO₂/Al₂O₃ electrodes with 1-methylbenzimidazole (MBI) as additives in the electrolytes have been detected. It is found that the TiO₂/Al₂O₃ electrodes immersed in the solutions of aluminum isopropoxide (acetylacetone as coordinate ligands) for 1 hour have obtained great increase of J_sc, and owned the improved cells efficiency by 17%. To discover the origins of this improved photovoltaic performance and investigate the electron properties of the cells, the electrochemical impedance spectroscopy (EIS) has been used both in the dark and under illumination at different applied potentials. It is proposed that with the coating of Al₂O₃, the adsorption of MBI cations at the surface of TiO₂ electrodes decreased with the decrease of the applied potentials, which resulted in the downwards shift of the conduction band position of the TiO₂/Al₂O₃ electrodes at the lower potentials. As a result, the charge transfer resistance Rct decreased, and chemical capacitance C_films increased. Under illumination, the decrease of Rct became smaller and the conductivities became larger, which was attributed to the recombination inhibition effect of Al₂O₃ coating to the photoinjected electrons. As a consequence, the electron lifetime and the effective diffusion length for the TiO₂/Al₂O₃ electrodes increased, leading to the great increase of J_sc. It is indicated that with the coating of Al₂O₃, the decrease of J_sc could be overcome when MBI is used as the additives of the electrolyte.

The aluminum back surface field used in p-type substrate hetero-junction with intrinsic thin film (HIT) solar cell is studied in this paper. The enhancement of material quality and the decrease of wafer thickness will make it necessary to passivate the back surface. It simply states the principle and formation process of aluminum back surface field, and studies the evenness of back surface field because it is necessary for high efficiency solar cell. Screen-printing and rapid thermal annealing were used to make aluminum back surface field to gain low recombination on the backside of solar cells. In this experiment, we analyze Al-BSF formed by taking different times and temperatures in which the temperature varied in the range between 620°C and 940 °C step 80°C and the time varied from 60 seconds to 180 seconds with a step of 30 seconds. Minority carrier lifetime with the back surface field was measured by microwave photoconductive decay (μ-PCD) device, analyze and get the optimal parameters of forming Al-BSF and further improve conversion efficiency of silicon solar cell.

Metamorphic multiple-junction soalr cells based on III-V compound semiconductor have advantages of more degree of freedom in selection of bandgaps of subcells. Recently, Spectrolab, Inc. reported a high conversion efficiency of 40.7% in a triple-junction Ga_0.44In_0.56P/Ga_0.92In_0.08As/Ge solar cell where the top and middle cells are lattice-mismatched to Ge substrate. Optimization of device structure of such metamorphic Ga_0.44In_0.56P/Ga_0.92In_0.08As/Ge solar cell is important to increase its efficiency. In this work, two-dimensional simulation has been performed on the metamorphic Ga_0.44In_0.56P/Ga_0.92In_0.08As/Ge solar cell. Efficiency dependence of the Ga_0.44In_0.56P/Ga_0.92In_0.08As/Ge triple-junction solar cell on the base layer thickness and the InGaAs graded buffer layer thickness has been investigated. It has been found that the efficiency depends significantly on the thickness of the GaInP base layer. The metamorphic triple junction solar cell has hightest efficiency when the thicknesses of the GaInP base layer, the GaInAs base layer and the GaInAs graded buffer layer connecting the Ge substrate and GaInAs middle-cell are 0.35 μm, 2.5 μm and 0.15 μm, respectively.

Light trapping is an important method to increase the efficiency of solar cells. In this work, we study the combined effects of photoelectrochemical etching and texturing to enhance light trapping. Porous silicon (PSi) as an antireflection coating is fabricated on the surface of a textured silicon layer by photoelectrochemical etching. The effects of different electrochemical conditions such as acidic solutions, illumination, current densities, and etching time on the solar cell parameters and surface reflectance from the silicon are evaluated. Our results indicate that the average reflectance of the surface is lower when electrochemical etching is combined with texturing and the PSi thus formed can serve as an antireflection layer in single-crystal silicon solar cells. Our SEM results acquired from samples prepared under different conditions show that the morphology of the textured surface can be improved by electrochemical etching.

Recently, the GaN based LED white light illumination technology has been developed rapidly. It is required to measure the p-n junction temperature of LED which has been encapsulated in the lamp with the temperature measurement error less than 1K. We present a spectroscopy approach to measure this p-n junction temperature of LED encapsulated in the lamp. The electroluminescence peak shift is used to determine the temperature difference between the junction and the ambient. At ambient temperature of 300K, the junction temperature can be determined by the formula of T=300+27.8▵λ_p-1.22▵λ_p ² with the unit of temperature T in K and electroluminescence peak shift ▵λ_p in nm. This method has been used on the high power lamp made by LED. The LED lamp has been fabricated for the illuminated application on the satellite and the spacecraft in China.

The light modulated Hall measurement system was set up in order to measure the minority carrier mobility of the p-type HgCdTe material. Minority carrier mobility is one of the main parameters for HgCdTe infrared photodetectors, because it determines the diffusion length of minority carriers, which plays a big role in the performance of optoelectronic devices. Therefore, it is important to get the minority carrier mobility in HgCdTe, so as to evaluate the material property before fabrication of photodetectors. By adding a modulated laser to the Hall system, the modulated Hall voltage was measured on p-type Hg_1-xCd_xTe(x=0.233) sample over a range of 0-1.8T in the magnetic field at temperature of 75K. The modulated signal is generated by the movement of excess photocarriers in the magnetic field, so it has a relationship with the magnetic field, the photogenerated carrier concentration and the electron and hole mobilities. Since the majority concentration and mobility can be derived from the Hall effect, the minority mobility and the photogenerated carrier concentration were obtained from fitting the light-modulated Hall voltage ▵V_H as a function of the magnetic field B. As compared to the references, the minority mobility we have obtained is reasonable, so the light-modulated Hall effect is an effective way to obtain the minority carrier mobility.

Our Toyota Technological Institute group has investigated various novel materials for solar cells from organic to III-V compound materials. In this paper, we report our recent results in conductivity control of C₆₀ thin films by metal-doping for organic solar cells, and mobility improvement of (In)GaAsN compounds for III-V tandem solar cells. The epitaxial growth of Mg-doped C₆₀ films was attempted. It was found that the epitaxial growth of Mg-doped C₆₀ film was enabled by using mica (001) substrate in the low Mg concentration region (Mg/C₆₀ molar ratio < 1). The crystal quality of the epitaxial Mg-doped C₆₀ film was improved drastically in compared with micro-crystalline film on glass substrate. Such drastic improvement of crystal quality in the epitaxial films resulted significant increase in conductivity. This result may indicate the significant increase of carrier mobility. Crystal quality improvement of CBE-grown GaAsN materials was investigated. We achieved the reduction of residual impurity concentration by chemical reaction control on the growing surface by modifying flow sequence of precursors and by increasing step density on the surface by using a vicinal GaAs substrate. Furthermore, the improvement in carrier mobility was observed, and it was suggested that the reduction of both residual impurities and N-related defects leads this improvement.

A distributed fiber lighting system with double-ended light sources is simulated numerically by using the software Matlab 7.0. The key factors affecting the lighting power and uniformity of the distributed fiber lighting system, such as light leakage rate, the distance of adjacent fiber loops and the number of the fiber loops are analyzed. The simulation results show that, the high lighting power and good uniformity are conflictive objects. The compromising effect is obtained on the condition that the number of fiber loops is 20, light leakage rate is 4.0% and the adjacent distance is 5 meters.

BiFeO3 thin films on different substrates were prepared via Sol-gel method. X-ray diffraction patterns indicated all the films were well-crystallized and gave X-ray peaks corresponding to BiFeO₃. The influence of different annealing temperatures and substrates to the Raman spectra was investigated. The Raman spectra of the 750 °C-annealed films gave almost the completed E modes. Compared with the film deposited on Si substrate, the positions of E modes peaks in Raman spectra of the film deposited on LNO-coated Si substrate shifted to higher frequency regions and the existence of the stress between the BiFeO₃ films and the substrates was considered to cause the shift.

Fe-doped mesoporous TiO₂ (M-TiO₂-Fe) thick films were prepared by sol-gel and screen printing process. Raman characteristics results show that the M-TiO₂-Fe thick film possesses a certain degree of the anatase phase, which may have advantages on photocatalysis and photovoltaic ability. Derived from small angel X-Ray diffraction (SAXRD), the films exhibit mesoporous structure with pore size around 7-8 nm. Eg of the films was obviously narrowed from 3.4 eV to 3.0 eV, which allows the thick films using more light to initiate photovoltaic process. Dye-sensitized solar cell (DSSC) based on M-TiO₂-Fe was structured and chlorophyl was used as sensitizers. The solar cells have an open circuit voltage above 260mV.

Mesoporous TiO₂/ZnO (M-TiO₂-xZn (x=10, 30, 50, 70, 90)) composite films have been prepared in sol-gel method by spin coating process. The films have sponge-like microcrystalline phase structures, as evidenced from TEM. The SAXRD patterns of M-TiO₂-xZn thin films suggest that the films exhibit mesoporous structure. The diameter/d value of thin films is around 11.76 nm, 7.88 nm, 6.89 nm, 10.02 nm and 13.78 nm, respectively. UV/vis transmittance spectra indicate that the fundamental transmittance edge of M-TiO₂-xZn films has a blue shift from 350 nm to 310 nm firstly, and then has a red shift. Photoluminescence (PL) spectra of M-TiO₂-xZn have three emission peaks, which are caused by near-band edge (NBE) emission and structural defects or/and impurities M-TiO₂-xZn thin films display a positive photovoltaic effect with the Zn content increased above 70 mol %, which may improve the energy conversion efficiency of M-TiO₂-xZn in Dye-sensitized solar cells (DSSC).

Barium strontium titanate (Ba1-xSrxTiO3) shows great potential in optical device applications, especially in infrared uncooled focal plane arrays (UFPAs) fabrication. In this paper, Ba0.5Sr0.5TiO3 ferroelectric thin films were successfully deposited on different substrates by pulsed laser deposition (PLD) with an aim to fabricate dielectric bolometer type infrared (IR) sensor. The microstructure, crystalline characterization and surface morphology of the film were studied by XRD pattern and Atomic Force Microscope (AFM). The fabricated thin films show a similar perovskite structure, have evenly distributed grains and dense, crack-free surface. The dielectric properties and ferroelectric properties of the films are also studied after deposition of the top Pt electrodes. Results show that the film has fine dielectric and ferroelectric properties and could be used for infrared sensor fabrication. Buffer layer effect on film properties is also discussed. The use of different buffer layers could strongly influence the film performance. As in optical device applications, the buffer layer effect should be considered in film fabrication.

Perforated GaN-based light-emitting diodes (LEDs) with an array of plasma-etched microholes penetrating through the active region were fabricated using lithography and plasma etching. Plasma damage on the microhole sidewalls led to an increase in junction leakage by up to seven orders of magnitude and a reduced light emission in the low injection regime. It was found that KOH can etch off the plasma-damaged materials, leading to a complete suppression of surface leakage currents. It however attacked metal contacts and increased the forward turn-on voltage. Thermal annealing removed damage in the near-surface bulk region, whereas (NH4)2S treatment only passivated the defect states at the immediate surfaces. Both methods produced a partial restoration of the forward-bias characteristics. It has been demonstrated that annealing at 700 °C used in conjunction with prolonged sulfide passivation can remove or passivate all plasma-induced defects and result in a complete suppression of surface leakage in the perforated LEDs. This work is an important step toward developing high-efficiency photonic crystal-integrated LEDs, in which light can only be coupled to radiation modes but the undesirable guided light emission is inhibited.

First of all, the article represents the character of photovoltaic effect and solar energy of semiconductor devices and the current situation of solar panel. It analyzes two difficuitys of the appplication of solar energy, the ways of enhancing solar cell performance and the barriers of producing high-efficiency PV modules. Solar photovoltaic technology, the technology use of solar energy and industry development trend are preticted.

In this paper, AZO (ZnO:Al) polycrystalline thin films is produced with strong adhesion to the substrate, which deposit on the glass substrate by PECVD (plasma enhanced chemical vapor deposition) method. The film with the sheet resistance as low as 89Ω/(see manuscript), and with transmittance as high as 85% in visible light spans has been obtain. The measurements of the film structure and the experiments to examine the influence of the film electro-optical property have been shown. This AZO film fabricated by PECVD method is a useful attempt, and the results are very important to the choice of actual process of the solar cell.

Ferroelectric Bi₂VO_5.5 (BVO) thin films have been successfully fabricated on p-type Si (100) substrates by sol-gel method. The microstructures and surface morphologies of BVO thin films were studied by X-ray diffraction and atomic force microscopy, respectively. Bi2VO5.5 thin films show c-preferred orientation, which indicates that the films match very well with the p-type Si substrate. Raman spectra measurements were carried out to study the lattice vibration modes of BVO thin films. Optical properties of the BVO were investigated due to their potential optical applications. And the optical properties of the BVO thin films have been studied by spectroscopic ellipsometric measurements in the wavelength from 400 nm to 1700 nm. The optical constant refractive index and extinction coefficient have been obtained. The resulting refractive index and extinction coefficient of BVO films show difference due to the different annealing process of the films, which implies the importance of the post annealing process. The increase of the refractive index could be understood by the higher density of the BVO films caused by the crystallization after annealing process. The Optical properties indicate that BVO films have potential applications in optical devices.

We perform density functional theory within the generalized gradient approximation to investigate infinitely wurtzite bare GaN nanowires in the [0001] direction. We report atomic and electronic structure of GaN nanowires with diameters of 10 and 16 Å. We find that relaxations on the facets are very similar to the ones in nonpolar (10-10) surfaces and play an important role in stabilizing the wires, and the average Ga-N bond length of the GaN nanowires decreases compared with bulk GaN. Both wires are found to be semiconducting and have a direct gap, with band gaps slightly smaller than that in bulk GaN. The shape of the band edge remains unaltered as the size of the nanowire increases. It is also found, for Ga and N atoms at the edge of the nanowires, the Ga 3p predominantly contribute to the edge states near the conduction band minimum, while the N 2p contribute mainly to the edge states near the valence band maximum. The present calculated results are helpful to gain a systematic understanding of structure, electrical properties of wurtzite GaN nanowires.

Nowadays, low temperature polycrystalline silicon thin film transistor (poly-Si TFT) has been the most popular subject in active matrix liquid display (AMLCD) and active matrix organic light emitting display (AMOLED). Relative to the other crystallization technique, aluminum-induced crystallization have certain advantages in lower temperature, and of course, lower cost than any other methods. This paper gives a research on the performance of poly-Si thin film fabricated by aluminum-induced electric field enhancing lateral crystallization at low temperature (<600°C). Raman spectra, X-ray diffraction and scan electron microscope were used to analyze the crystallization state, crystal structure and surface morphology of the poly-Si thin film. Results show that the poly-Si thin film has good crystallinity, and the electric field has the effect of enhancing the crystallization when direct current electric voltage is added to the film during annealing. In addition to this, the metal aluminum induced crystallization was monitored in the whole progress when Al was diffusing into the a-Si thin film by measuring resistance of crystallizing thin film. The poly-Si thin film fabricated by this low temperature electric enhancing aluminum-induced crystallization technique was obtained. The results show that it is suitable for P-Si TFTs which is widely used in AMLCD and AMOLED.

The inclusion of a back surface field (BSF) can significantly improve the efficiency of GaAs solar cells due to a better collection of photogenerated minority carriers. In this work, the efficiency of a single GaAs solar cell has been optimized by varying the material properties of AlGaAs back surface field layer using an advanced commercial software, Crosslight APSYS simulator. By optimizing the Al composition and width of the back surface field layer, a maximum efficiency 25.660% is obtained when Al composition is 0.25 and the width is 0.3 μm. The band diagrams, 2-dimensional relative energy density profile and I-V curve of the device structure with the optimal back surface field layer are also obtained by APSYS.

BaTiO3 thin films with different dopants of Fe and Co were prepared by sol-gel technique on Si and LaNiO3 coating Si substrates respectively. The x-ray diffraction patterns showed that all the films were perovskite structure and the change of lattice constant caused by dopants was undetectable. Atomic Force Microscope (AFM) was used to characterize the surface morphology of the thin films. The surfaces of films were uniform and dense except Co-doped BaTiO₃ film on Si substrate. The Raman spectra showed the Fe dopant could improve the crystal quality of BTO films on these two different substrates. The results of UV reflectance for BTO thin films prepared on Si substrates showed that the reflectance peaks of Fe-doped BTO film moved to the low frequency. The Pt top electrodes were fabricated on BaTiO₃/LaNiO₃/Si to form a metal-ferroelectrics-metal structure and the dielectric properties of the thin films were carried out by impedance analyzer. It was found that Co dopant could increase the dielectric constant of BTO film to some extent and the Fe dopant could decrease the dielectric constant of film below 30 kHz. Both of the dopants could increase the dielectric loss of the films with the frequency increasing.

The epitaxial layer quality of Al_xGa_1-xN (x>0.6) on sapphire substrate grown by metal organic chemical vapor deposition (MOCVD) needs to be further improved. In this paper, we evaluated the properties of defects, lattice mismatch between epitaxial layer and substrate, crystal quality and conductivity for these high Al mole fraction materials from the viewpoint of fabricating high performance solar blind detectors by comprehensive utilizing various undamaged measurements. The measurement of transmission spectrum was used to evaluate the absorption edge, band gap, mole fraction of Al content, hetero-epitaxial interface, and transmissivity in the ultraviolet spectral range. X-ray diffraction (XRD) was used to measure the component of the AlGaN material, uniformity of the material and crystal quality. The conductivity of the surface layer of the AlGaN film material was obtained by using high precision current-voltage curve measurement. In short, the material quality, optical and electrical properties, and uniformity for high Al mole fraction AlGaN epitaxial layers were qualitatively or quantitatively measured and analyzed. These works lay the foundation for manufacturing high performance solar blind ultraviolet detectors based on high Al mole fraction AlGaN epitaxial materials on sapphire substrate.

A multi-step rapid thermal annealing process of Ti/Al/Ni/Au was investigated for ohmic contact of AlGaN/GaN high electron mobility transistor(HEMT).The samples were studied by Transmission Line Model(TLM),Scanning Electron Microscopy(SEM) and Auger Electron Spectroscopy(AES) measurements. By the multi-step annealing process, the specific contact resistance was decreased and the surface morphology was improved. The AES measurements showed that the limitation indiffusion of Au and outdiffusion of Al were account for the surface morphology improvement.

RMO₃ (R=rare earth, M=Fe, Mn, Ni) is a kind of multi-ferroelectric material1 while Lu is a element which has been widely used in electroluminescence area. Material constituted with Fe and Lu is thought to have special properties on electromagnetic coupling due to the reactivity of Lu and the magnetism of Fe. For example, LuFe₂O₄ is a new type of electric ferroelectric material which has become more and more concerned after Ikeda reported it in the Nature magazine in 2005.² We successfully fabricated another LuFeO₃ thin film with sol-gel method on Si substrates with different constituents, and analyzed the structural, optical properties of the samples. We investigated the optical properties with UV-Vis, PL, etc. After Mn was doped, the properties were compared with the previous ones.

Silicon is one the most extensively used photovoltaic materials because of its relatively low cost and well established fabrication processes. Therefore, development of technologies that can improve the energy efficiency of silicon solar cells is important. In this report, a novel solar cell structure based on 3D (three-dimensional) macroporous silicon p-n junctions and the corresponding mathematical model are proposed. The structure and electrical performance of the silicon solar cell with the 3D p-n junction are analyzed. Significantly increased efficiency can be achieved due to the better carrier collection and light absorption. Our results reveal improved photocurrent and other characteristics, thereby demonstrating the validity of the improved solar cell structure.

This paper reports on luminescence property of the Dy³⁺-doped tellurite glasses. The samples are studied by absorption and visible emission spectra. The measured emission spectrum of Dy³⁺ glass has revealed two main bands at 484 nm (⁴F_9/2→⁶H_15/2) and 574 nm (⁴F_9/2→⁶H_13/2) when pumping with the wavelength of 325 nm. The concentration quenching occurred as Dy³⁺ concentration increased beyond 2 mol%. The chromaticity coordinates of these samples are close to white light, which implies that the glasses might be a potential candidate for white lighting through an appropriate combination.

We have investigated wet chemical etching of Al0.65Ga0.35N in 20% (by weight) aqueous KOH solutions at 85, 95 and 102 °C. The etch rates were 0.48, 0.64 and 0.96 μm/min, respectively. Scanning electron microscope, atomic force microscopy, Auger electron spectroscopy and x-ray photoelectron spectroscopy were employed to characterize the surface morphology and stoichiometry before and after wet chemical etching. Experimental results show that aqueous KOH solutions can effectively etch Al_0.65Ga_0.35N. SEM results show that the root-mean-square (rms) roughness increased from 16.189 to 50.496 nm. Degradation in surface smoothness is attributed to selective anisotropic wet chemical etching. The AES measurements show that after the untreated sample was wet chemical treated in a 20% KOH solution at 85 °C for 15 seconds, the oxide formed in the surface was removed and a lower content of oxide layer near the surface was formed and the N content is higher. XPS measurements show that the banding energies of Ga 3d shifted to low energy direction after the untreated sample was successively wet chemical treated. It indicated that the atom Ga tended to form Ga-N rather than Ga-O bonding on the surface after KOH solution treatment. The damage and oxide layer induced by dry etching processes was effectively removed by wet chemical treatment and the damage surface was refreshed.

Two kinds of deep blue emission materials (** and *** )were synthesized by reduction coupling Method. The characteristic of the two materials have been studied by UV-vis absorption spectra, thermogravimetric analysis(TGA), differential scanning calorimetry(DSC) and fluorescence spectroscopy. The two materials emit strong blue fluorescence under the excitation of UV light. The induction of Br ion may induce the red-shifted 15 nm of absorption in the UV-visible light range. UV absorption spectra show the absorption energy of complexes mostly from ligands.

Using a variety of experimental, alumina nitride (AlN) based diluted magnetic semiconductors (DMSs) are found to exhibit ferromagnetic properties at room temperature by many groups. The origin of ferromagnetism in DMSs is ambiguous and difficult to be clearly identified. The geometrical structure of V doped 32-atom supercell of AlN was optimized by using the ultra-soft pseudopotential method of total-energy plane wave based on the density functional theory (DFT) . Density of states and band structure were calculated and discussed in detail. The results revealed that the V dopants were found spin-polarized. Band structures show a half metallic behaviour. The ferromagnetic ground state in V-doped AlN can be explained in terms of p-d hybridization mechanism. These results suggest that V-doped AlN may present a promising dilute magnetic semiconductor.

The geometrical structure of GaN (0001) surfaces supercell of GaN was optimized by using the ultra-soft pseudopotential method of total-energy plane wave based on the density functional theory (DFT) .Electronic structure, Density of states , band structure and optical properties were calculated and discussed in detail.Geometry optimization indicates that largest atomic relaxation occurs to metal atoms(Ga) in surface layers where all atoms are displaced inward,and the interlayer distances vary large, total polarization strength is strong. The band gap of GaN (0001) surface is obviously narrower than that of GaN, the luminescence spectra shift red.The two aspects go against making high efficiency white-light LED.This paper provides theoretical foundation of GaN (0001) surface and the direction fo making high efficiency white-light LED form first-principles calculation.

Light can emit from light emitting transistor of III-V materials. The pn-n+ structure of light emitting transistor, which has an additional n-n+ heterojunction between the base and electron emitter, is suggested. The base voltage can control the light output effectively. The functional principle of light emitting transistor is illuminated. A model about the abrupt isotype heterojunction in the base has been utilized to describe thermionic electron transport, current density and potential barrier in such a device. The model is used to explain the underlying mechanisms of the present devices.

Improving light extraction efficiency (LEE) is important to enhance efficiency of light-emitting diodes (LEDs) and the issue has been studied comprehensively. A GaN-based LED chip with diamond shaped is presented in this letter and LEE was analyzed. The LEEs of the conventional chip and flip chip with different angle of slant from 0° to 20° were obtained through Monte-Carlo ray tracing method, which is a useful and efficient way in studying the LEE of LED. The results show that the LEE of the chip with obliquity enhanced by 20.2% compared with conventional rectangle chip with mirror bottom surface, however, there is no improve of the LEEs of flip chip and conventional chip with diffuse surface.

This paper investigates which dopping concentration or layer thickness should be used to design practical GaInP/GaInAs/Ge triple-junction cells in order to optimize their performance. A rigorous model includes optical and electrical modules is developed to simulate the external quantumn efficiency, photocurrent and photovoltage of the GaInP/GaInAs/Ge tandem solar cells. It is found that cell efficiency strongly dependend on the top cell thickness and doping concentration at base and emitter layers. Proper structures of the tandem cell operating under AM0 ("air mass zero") illumination are suggested to obtain high efficiency.