This paper introduces briefly the status of existing focal plane arrays in the world. A more detailed description of the Laboratoire Infrarouge (LIR) - SOFRADIR Technology is given. Results concerning scanned linear arrays and staring arrays are given at 77 K and 200 K. Future prospects concerning materials and readout circuits are presented.

The term 'smart sensors' refers to sensors which contain both sensing and signal processing capabilities with objectives ranging from simple viewing to sophisticated remote sensing, surveillance, search/track, weapon guidance, robotics, perceptronics, and intelligence applications. In a broad sense, they include any sensor system covering the whole electromagnetic spectrum: this paper deals specifically with a new class of smart sensors in infrared spectral bands whose developments started some years ago, when it was recognized that the rapid advances of very large scale integration (VLSI) processor technology and mosaic infrared detector array technology could be combined to develop new generations of infrared smart sensor systems with much improved performances. Thus, sophisticated signal processing operations will be developed for these new systems by integrating microcomputers and other VLSI signal processors within or next to the sensor arrays, on the same focal plane, avoiding complex computing located far away from the sensors. Recently this approach has achieved higher goals by a new and revolutionary sensor concept which introduces inside the sensor some of the basic functions of living eyes, such as dynamic stare, dishomogeneity compensation, spatial and temporal filtering. New objectives and requirements of these new focal plane processors are presented for this type of new infrared smart sensor system. This paper concerns the processing techniques limited to the front end of the focal plane processing, namely, the enhancement of target-to-noise ratio by background clutter suppression and the improvement in target detection by a smart pattern correlation thresholding.

Since 1984, infrared sensors devices have been developed in the CEA-LETI laboratories for astronomical observation in the 4-17 micrometers wavelength band using Si:Ga detectors. These devices are to equip ISOCAM, a camera which will operate from ISO (Infrared Space Observatory), the European satellite expected to be launched in May 1993, and C10(mu) , a French astronomical camera which will be based at the CFHT (Canadian French Hawaii Telescope). In this paper, a brief description of the devices and their operating conditions, as well as main preliminary results, are given.

The noise equivalent temperature difference (NETD) is one of the most convenient measures used in describing performance of infrared systems as thermographs and radiometers. The NETD expression is also contained as a kernel within any minimum resolvable temperature difference (MRT) and minimum detectable temperature difference (MDT), so the conclusions to be reached relative to NETD apply to MRT and MDT as well. For reasons of convenience, some assumptions have been made in defining (measuring and deriving relation for) the NETD. However, for a variety of practical purposes in the field, these assumptions are not satisfied. Consequently the conventional laboratory NETD is applicable under certain favorable laboratory conditions. Therefore the typical, laboratory NETD expressions found in the literature cannot be simply applied for infrared systems under field conditions. In this paper the practical, field NETD expression is derived. It incorporates none of the assumptions which have been used in defining and deriving the laboratory NETD expression. Therefore, the given expression can be applied to assessment of infrared systems capabilities under field conditions.

Directional couplers based on titanium-diffused lithium niobate are potentially attractive for applications requiring polarization-independent optical switching or modulation. Although directional couplers with >25 dB switching extinction ratio for both TE and TM modes have been fabricated, polarization independence and reproducibility are difficult to achieve. Presumably, uncontrollable process variations result in different coupling strengths and switching characteristics in nominally identical devices. These variations can be compensated by using the so-called reverse-(Delta) (beta) design, where the device electrodes are split into two different sections and tuned with separate voltages to obtain maximum cross-state extinction. The addition of a second control voltage complicates characterization of the devices, since full characterization requires plotting switching in a two-dimensional voltage space. The authors have developed a system to automatically perform two-dimensional switch characterizations. The resulting data display asymmetries which can be analyzed within the framework of coupled mode theory. The analyses indicate that two factors contribute to the observed asymmetry: a static, fabrication-induced difference in propagation constant (beta) between the two waveguides, and an applied-field dependent evanscent coupling strength.

The authors report on techniques used to manufacture IR diffractive elements in chalcogenide glasses and on measurements of the material properties relevant to the performance of these elements. The characteristics of the elements produced are also presented and compared with theoretical predictions. The fabrication process used is based on the photodissolution of Ag into amorphous As-S films. Both surface relief and volume phase modulated transmission elements have been made. The transmission of Ag photodoped and undoped As-S films was found to be >80% over the range 2-12 micrometers for films up to 2 micrometers thick, the main loss mechanism being reflection. The difference in refractive index between Ag photodoped and undoped As-S over the range 0.5-12 micrometers was 0.5 for the most heavily doped material, so that high modulations are achievable for phase gratings. Theory suggests that for these As-S materials, green illumination (e.g., 514.5 nm) is the most efficient for producing the deep structures required for many of these IR elements. Surface relief structures can be produced by removing undoped material with an alkali etchant (e.g., NaOH). For transmission gratings, any remaining metallic Ag must be removed, to avoid high losses: the most successful Ag etchant was found to be Fe(NO3)3 in water. For the bulk holographic transmission gratings produced, efficiencies of >33% were observed for first diffraction orders measured in air at 632.8 nm, the main loss mechanisms being absorption and reflection, with some scatter. Measurements at 1.5 micrometers have given efficiencies of >30%, stability requirements during holographic recording currently being the main limitation to higher efficiencies at these and longer wavelengths. The results of a theoretical analysis based on numerical solution of the appropriate coupled-wave equations and taking into account bulk losses with phase and absorption modulation are in good agreement with the observed diffraction efficiency data. Given the low material absorption in the IR, theoretical studies show that, with suitable coatings, >95% efficiency should be possible for properly optimized bulk gratings and blazed zone plates.

Single longitudinal mode lasers emitting at 1.5 micrometers are attractive as light sources for low transmission loss (0.15 dB/km) and low dispersion (10 ps/nm/km) optical transmission systems. In distributed feedback (DFB) lasers, the corrugation grating near the active layer selects the emission wavelength. The realization of very good uniformity in composition and thickness on a large wafer allows a uniform Bragg wavelength. In this paper, the static characteristic and stability of DFB lasers emitting at (lambda) equals 1.55 micrometers are presented. It is important to know these data in order to compute the equivalent noise circuit of the DFB laser. The voltage noise of the laser diode Svd (V2/Hz) and the coherence function (gamma) vd-Iph2 between electrical noise and optical noise SIph (A2/Hz) are shown for the first time. Analytic expressions for the electrical noise spectral density Svd(f) and the optical noise spectral density SIph(f) agree with experimental results given by noise measurements.

A method for the colorimetric characterization of color matrix CCD sensors has been developed. This method is based on measuring the spectral responses of the sensor with on- chip color filters and then simulating the processes that take place in a camera. Optimizing the simulated processes enables each sensor to be characterized by providing colorimetric fidelity parameters.

The photoelectric characteristics of silicon phototransistors are investigated. The device consists of three regions with different types of conductivity. The operation of the phototransistor is based on the hot carrier emission from the emitter into the base under IR laser irradiation. The current-voltage measurements on the emitter-base junction show that photo-induced current increases with the increase of forward bias voltage and decreases when reverse bias is applied. The characteristics of the collector photocurrent versus the collector- base voltage in the common-base configuration are very similar to static collector current vs the collector voltage characteristics of an ordinary bipolar transistor. Furthermore, the collector photocurrent increases with an exponential law when the emitter-base junction is forward biased.

A brief survey of the basic detector materials used in the more important infrared detector technologies including thermal, platinum silicide related, low-dimensional solid, and photon is given with the emphasis on the significance of their material aspects. The main thrust of the paper, however, considers recent advances in the materials aspects of mercury cadmium telluride (MCT) and includes work on low temperature growth, p-type doping, and substrates.

The current status of molecular beam epitaxy (MBE) of CdTe and HgCdTe on Si(100) is reviewed. CdTe and HgCdTe grow in the (111)B orientation on Si(100); monocrystalline films with two domains are obtained on most nominal Si(100) substrates, single domain films are grown on misoriented substrates and on nominal Si(100) preheated to 900-950 degree(s)C. Double-crystal x-ray rocking curves (DCRCs) with full-width at half-maximum (FWHM) as low as 110 arcsec are reported for HgCdTe on silicon; these layers are n-type, and electron mobilities higher than 5 X 104 cm2V-2s-1 are measured at 23 K for x equals 0.26. Excellent thickness and composition uniformity is obtained: standard deviation of the CdTe thickness 0.4% of the average thickness on 2-in. and 2.3% on 5-in., standard deviation of the Cd concentration in the HgCdTe layers 0.6% of the average concentration on 3-in. and 2.4% on 5-in. First results regarding growth of CdTe on patterned Si substrates are also reported.

Buried heterostructure (BH) PbSnTe lasers were prepared in a two-stage MBE growth. Lasers with Pb1-xSnxTe (xequals0; 0.04; 0.05; 0.068; 0.095) buried active layer and a buried quantum well (BQW) Pb0.932Sn0.068Te active layers have been manufactures. A maximum continuous wave operating temperature of 203 K was recorded for a lattice matched PbTe active layer BH laser, and a maximum operating temperature of 189 K was recorded for the BQW laser.

A brief review is given of the development of a metalorganic molecular beam epitaxial system for Hg-based II-VI semiconductors. Recent results on the growth of HgZnTe, HgCdTe, and iodine-doped CdTe epitaxial layers are presented and demonstrate the potential of this technique for the growth of high-quality materials.

In the present paper the optical transmittive properties of different thickness CVD ZnSe and CVD ZnS Cleartran samples are analyzed using BTDF at the He-Ne laser wavelength. The measurements obtained determine the combined surface and bulk scattering. Surface scatter dominates over bulk scattering for ZnSe, while for ZnS Cleartran the main contribution to the scattered field is given by the bulk. A criteria to assess the material thickness as a function of its scattering characteristics when it is used to realize multispectral imaging system windows is discussed. The results suggest that the thickness of ZnS Cleartran windows in a multispectral imaging system must not exceed few millimeters.

The intrinsic carrier concentration, electron effective mass ratio, and the reduced Fermi energy are calculated for Hg1-xMnxTe with 0.08 YLD (DOT) pYLD method (Kane model). By fitting the calculated nonparabolic ni values to the expression for parabolic bands, the following approximation for the intrinsic carrier concentration has been obtained: ni equals (4.615 - 1.59x + 0.00264T - 0.0170xT + 34.15x2)1014E3/4T3/2exp(-5802Eg/T) in cm-3, where Eg is in eV.

The interference method for reconstruction of the three-dimensional function of an absorption coefficient is presented in this report. The method is based on the use of the nonlinear dependence effect of the refractive index of various media on laser radiation intensity. Powerful laser radiation changes refractive index of specially chosen media to a great extent. These changes can be read out by an interferometer with the aid of probing radiation at any convenient wavelength. The change of the original power density distribution of the radiation under study will cause the change of a form and quantity of fringes. An absorbing (partially diffusing or reflecting) object, introduced into the studied beam, will by no means cause the same changes. Therefore, the change of the form and quantity of the fringes will contain information about an object introduced into radiation.

The phase diagram of the quaternary AlInAsSb system has been investigated. These data have been used for LPE growth of the AlxIn1-xAsySb1-y solid solutions lattice-matched to InAs (with Al mole percentage in the range 0.0-0.08). A band gap was determined for this material in dependence on the composition by photoluminescence measurements. The band gap of the solid solution in the investigated range of composition corresponds to a wavelength from 3 micrometers (x equals 0.0, Eg equals 0.414 eV) to 2.5 micrometers (x equals 0.08, Eg equals 0.49 eV).

Deviation from stoichiometry to Ga2S3 excess is shown to be an effective method to obtain mercury thiogallate crystals with strong 670 nm luminescence, photosensitivity at (lambda) < 700 nm and large light-sums storage. The smaller Ga cations are able to create easier antistructural Ga(mu g) defects, to occupy stoichiometric voids, and interstitial sites are supposed to be responsible for the changes.

Optically nonlinear side chain polymers have been applied in passive and electro-optically active waveguiding structures operating in the visible and near infrared wavelength ranges. In order to possess second-order optically nonlinear effects, the polymers have been poled with electric fields on the order of 100 V/micrometers , and electro-optic coefficients of about 20 pm/V have been induced at the nonresonant wavelength of 1330 nm by this method. By successive spincoating of different polymers with adapted refractive indices, multilayer structures have been made possessing waveguiding properties. By applying the photobleaching method through a mask, local decrease of the refractive index is induced, resulting in monomode or multimode channel waveguides. Optically passive structures and active structures such as straight and bend waveguides, phase shifters, Mach-Zehnder interferometers, and directional mode couplers have thus been made. Switching and modulation voltages are on the order of 10 V, combined with modulation ratios on the order of 15 dB. The applied technology permits the integration of light sources with waveguides and may open the way for mass production of cost-effective optical components.

A high-Tc superconducting microbolometer has been constructed using a Y1Ba2Cu3Ox thin film deposited on a MgO substrate. Radiation is coupled to the 20 micrometers and 4 micrometers wide bolometer by means of a logarithmic periodic antenna designed for use in the 90 micrometers to 600 micrometers wavelength band. The bolometer response to a 570 K blackbody was measured at 500 Hz. The responsivity was found to be 25 V/W with an NEP of 4 * 10-10 W/Hz1/2 assuming an absorptivity value of 1. Excess noise is seen to behave proportional to 1/f(alpha ), with (alpha) close to one.

The optical anisotropy of GdBa2Cu3O7-x epitaxial films has been experimentally investigated by use of ellipsometry and polarized reflectance measurements. The individual principal components of the dielectric tensor of this new high-Tc compound are derived from ellipsometric measurements performed in the visible and infrared frequency regions. Our results show that this compound is highly anisotropic in the near infrared region, and that it exhibits strongly free-electron-like behavior in the c-axis direction at optical frequencies.

This paper shows the feasibility of the determination of the complex conductivity in the frequency range 18-26 GHz on YBaCuO superconducting films. The method used offers the advantage of being nondestructive and allows the reutilization of the sample for realizing microwave circuits. As an application, the authors realized with conventional photolithography resonators operating in the frequency range 1-18 GHz. Their resonance measurement at 78 K made it possible to infer the surface resistance and consequently to compare this value with the one deduced from the conductivity measurements.

The realization of an experimental setup for the characterization of a high critical temperature superconductor (HTCS) thin film by a microwave measurement is described. This approach allows HTCS parameters, like surface resistance in microwaves, to be determined from experimental measurements.

Growth of ultrathin SimGen [m monolayers (ML) Si, n ML Ge] strained layer superlattices (SLS) by molecular beam epitaxy is reported. Diode structures (doping sequence p+-n-n+ on n+-substrate and n+-n-p+ on p+-substrate) were grown for optical device applications where strain symmetrization of the SLS by a thin homogeneous buffer layer was used. The concepts of bandstructure folding and strain adjustment of the SLS by a thin (approximately 50 nm) Si1-ybGeyb alloy buffer layer are described. The folded bandstructure with its transition matrix elements as a function of period length is calculated. Various characterization tools such as x-ray diffraction, transmission electron microscopy, Rutherford backscattering, Raman spectroscopy, and photocapacitance measurements are used to analyze the growth quality, strain distribution, periodicity, interface sharpness, and optical properties of the superlattice. Results from recent optical experiments such as photoluminescence and ellipsometry giving hints of a direct bandgap transition in a 10 ML Si6Ge4 SLS in the near-infrared spectral region (hwapproximately equals 0.8 eV) are compared with PL data from SiGe alloys. Device applications offering the possibility of a monolithic integration of superlattice devices with complex silicon based electronic circuits are discussed.

One of the areas of current interest in basic semiconductor research in Si-integrated optoelectronic devices. Among the several existing routes investigated to realize this aim, the use of semiconducting silicides is of high interest since such a technology would put silicon at the roots of both microelectronics and optoelectronics. Only a few silicides are believed to display semiconducting properties. FeSi2 with a direct gap of 0.89 eV appears as one of the most promising materials since epitaxy on silicon substrates (111) and (100) has been reported. In order to give some new insights on this epitaxial growth, which is a key point for any further development, the authors present results on the preparation of epitaxial FeSi2 thin films grown in a molecular beam epitaxy machine on (111) silicon wafers. By means of in situ real-time reflection high energy electron diffraction, the formation of various silicide phases has been observed during the solid phase epitaxy process.

Rare-earth silicides form very low Schottky barriers on n-type Si ( 0,3 eV) and have good electrical and thermal conductivity. They are attractive for applications in JR detectors or as ohmic contacts on Si. We have studied, by surface techniques (LEED, XPS, UPS and AES), the formation and the electronic properties of erbium silicide thin films epitaxially grown on Si(1 1 1) substrates. Erbium was evaporated under ultra-high vacuum on clean Si(1 1 1) (7x7) surfaces and several methods of solid phase epitaxy were used. Jt was found that the "template" method, successive cycles of deposition of 20 A Er - 25 A Si double layer followed by annealing gave the best film morphology. The silicide composition (1 Er : ' 1.7 Si) was attained after annealing of the deposits at 560- 600° C. The crystalline quality of the films improved upon annealing at higher temperature and sharp LEED spots were obtained at 800 - 900° C. The chemical shifts of the Si and Er XPS core-levels were very weak, , - 0.4 eV for Si 2p and negligible for Er 4d, indicating a weak charge transfer and metallic bonding. The valence band of epitaxial (0001) ErSil.7, formed by hybridized Er sd - Si sp states, spread from E to '-' - 4.5 eV, leaving the Er 4f states unaffected. Angle resolved UPS revealed great energy E (k) dispersion in the surface plane but undetectable energy dispersion along the perpendicular to the surface, suggesting a 2 D character of the siicide films.

The need for increased resolution and sensitivity in IR systems applications has provided the impetus for the development of high-performance second-generation staring focal plane array technology. Previously, the availability of these focal plane array components has been limited and the costs associated with delivery of useful hardware have been high. Utilizing proven InSb detector technology and foundry silicon CMOS processes, a high performance, affordable hybrid focal plane array and support electronics system has been developed. The 128 X 128 array of photovoltac InSb detectors on 50 micrometers centers is interfaced with the silicon readout by aligning and cold welding indium bumps on each detector with the corresponding indium bump on the silicon readout. The detector is then thinned so that it can be illuminated through the backside. The 128 X 128 channel signal processing integrated circuit performs the function of interfacing with the detectors, integrating the detector current, and multiplexing the signals. It is fabricated using a standard double poly, single metal, p-well CMOS process. The detector elements achieve a high quantum efficiency response from less than 1 micrometers to greater than 5 micrometers with an optical fill factor of 90%. The hybrid focal plane array can operate to a maximum frame rate of 1,000 Hz. D* values at 1.7 X 1014 photons/cm2/sec illumination conditions approach the BLIP value of 9.4 X 1011 cm(root)Hz/W with a capacity of 4 X 107 carriers and a dynamic range of greater than 60,000. A NE(Delta) T value of .018 C and a MRT value of .020 C have been measured. The devices operate with only 3 biases and 3 clocks.

The analysis of a magneto-concentration effect carrier-depleted IR photodetector is reported. The device is a lightly doped narrow-gap photoconductor with a high backside surface recombination velocity, placed in a magnetic field. Due to action of the Lorentz force, the carrier concentration in the most parts of the device is highly reduced. As a result the I-V characteristics exhibit saturation and negative dynamic resistivity. The Auger generation and recombination processes are highly suppressed, resulting in a decrease of noise current. This makes it possible to improve dramatically the performance of IR devices. For example, the background limited performance is predicted for 10.6 micrometers (Hg,Cd)Te devices operated at 230-250 K.

The first direct measurements of a periodic variation in the axially dependent transmission characteristic of a hollow circular cross-section waveguide are described. The experimental results are explained in terms of the excitation and propagation of the two lowest order EH1n modes. As these modes propagate along the waveguide, they run in and out of phase with one another, causing a periodic refocusing of the input beam. Midway between the refocusing points, intensity profiles of a 'doughnut' form are produced. It is proposed that these dramatic field variations produce an axially dependent variation in the waveguide attenuation coefficient, thus explaining the experimental results.

The free-electron laser (FEL) amplification mechanism is discussed, including the influence of the electron-beam quality (energy spread, emittance, stability) on the FEL performance. Considerations regarding the choice of the electron accelerator are presented, and some characteristic properties of the laser radiation are discussed. An overview of FEL-facilities for the infrared spectral region, which are being designed and built worldwide, is given.

The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications are given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method. These techniques make it possible to define superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches are presented for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y- on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTs phases to fabricate novel, monolithic devices. We discuss recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors are presented.