This paper presents SAT indium antimonide Charge Injection Devices (C.I.D) Technology, post focal plane signal processing and some applications. These detectors are constituted by MOS capacitors realized on InSb wafers using integrated circuit-like processing. When a negative voltage is applied to the structure (put it into depletion) the capacitors form integrating detectors for use in 3-5 pm band. Linear arrays constituted by a line of single capacitors, matrix arrays constituted by a group of two coupled MOS capacitors, collect and store photon generated charge carriers. In the last case, the selection of a site is accomplished by X-Y decoding technique. SAT manufactures currently line arrays with as many as 64 elements and staring arrays with as many as 32 x 32 elements. Works about 128 elements line arrays and 64 x 64 elements matrix array is being develloped. After a brief description of CID mechanisms this paper presents detectors manufacturing and focal plane evaluation method. Staring infrared imagers possess an inherent fixed pattern noise which is determined by the non uniformities in quantum and transfert efficiencies, dark current, electrical coupling circuitry. These defaults must be compensated. On the other hand, staring arrays are characterized by a low integration time : so, a frame averager must be used to be compatible with equipments frame rate and increase signal to noise ratio. This post signal processing used in an experimental camera is to be described. These works are defined in a contract with Direction des Recherches Etudes et Techniques (n° 83.34.073). Other civil and military applications are presented.
Thin silicon dioxide films were prepared by photo chemical vapor deposition. IR absorption and Auger electron spectroscopy have shown that the dominant components of the oxide are silicon and oxygen with little amount of hydrogen. MIS capacitors were constructed on InSb substrates. C-V characteristics of the MIS capacitors were measured, and mid-gap interface state density of low 1012 cm-2eV-1 was determined. The amount of hysteresis observed was found to be about 10% of the inversion bias voltage. Annealing studies were also conducted to improve the electrical properties. After annealing, mid-gap interface state density was reduced to 5x10-11 cm-2eV-1 and the amount of hysteresis reduced to 5% of the inversion bias voltage.
Infrared detectors consisting of photovoltaic CdHgTe diode arrays coupled to silicon multiplexing circuitry have been demonstrated in formats up to 64 x 64. In the long and intermediate wavelength bands respectively, progress is reported on 64 x 64 co-ordinate addressed hybrids, and on 64 x 64 CCD hybrids. Recent developments in hybrid technology and array assessment have demonstrated the feasibility for much larger arrays. Imaging studies have shown that NETDs of less than 0.05K are currently being achieved at 12.0μm cutoff wavelength using co-ordinate addressed arrays, and sensitivities less than 0.03K are being achieved at 5.0μm using CCDs. In the case of linear multiplexed arrays, conventional parallel input CCDs are compared with a new multiplexer architecture based on NMOS technology.
Frequency response was measured by detecting the heterodyne beat signal between a tunable Pb Sn Te diode and a CO2 laser. Experimental results and the SAT Hg Cd Te photodiode technology are presented. Frequency responses are measured above 8 GHz.
Heterodyne systems operating in the infrared have been developed for rangefinding, velocity measurement and anemometry. More recently such systems have been extended to cover vibration detection and active imagery (ref. 1). These advanced systems have frequently used a cadmium mercury telluride photodiode operating at 77K as a wide bandwidth, high sensitivity detector of CO2 laser radiation. In practical systems this type of detector may be disadvantageous because of the requirement for high pressure air to achieve the operating temperature.
Anamorphic detector optics can be used to improve the horizontal spatial resolution of SPRITE based thermal imagers, and their retrofitting is possible in many existing imagers. However, the effect on the detector's thermal sensitivity is dependent on detector and system parameters, and must be carefully analysed. Example systems are used to illustrate this analysis.
A practical technique is described for defining with high precision the active area of each element of an array of pyroelectric detectors when these detectors are required to be of small dimensions, closely spaced and separated from each other by complete reticulation. The technique makes use of a thin film array of. IR absorbing elements with the required active area and thermally coupled to a corresponding array of pyroelectric elements, each of which has an area less than the active area and requires a relatively low dimensional to4erance. A design is proposed which is suitable for chopping frequencies approaching 103 Hz.
It is well known that pyroelectric infra-red detectors can exhibit high levels of piezoelectric microphony. Microphonic signals manifest themselves as an unwanted source of noise when the devices are subjected to accelerations or vibrations from the environment. Accurate models have been developed to describe the strains occurring in an active pyroelectric layer mounted on a substrate as an IR detector, from which piezoelectric microphony levels can be predicted. It has been shown that the main source of noise is generated by the lateral strain in the pyroelectric, caused by a flexing of the substrate mounting. This strain engenders a microphonic voltage via the piezoelectric d3, coefficient. The noise voltage is thus critically dependent upon the nature of the mechanical mounting. A second, much smaller, source of microphony is caused by the self-loading of the pyroelectric elements when subjected to accelerations parallel to the polar axis. This generates a thickness-mode noise signal via the piezoelectric d33 coefficient which is independent of the mounting arrangement.
A pyroelectric/CCD hybrid array has been designed and fabricated The array has 16 x 16 elements at 256 micrometers pitch. The hybrid uses a Pb/Sn solder bump technique. The custom CCD includes a high injection efficiency and Image Difference Processing to remove fixed pattern noise. An NETD of 0.4°C at 25 Hz frame rate has been measured.
The responsivity of narrow gap photo-detectors (e.g CMT) can be increased, and noise processes reduced by the use of minority carrier exclusion in a suitably designed structure. It is found that, while diffusion plays no role within the exclusion region, it is a major factor in determining its size. Experimental data excellently match computer modelled predictions, showing that the reduced electron concentration in an uncooled device leads to significantly improved photoconductor performance.
The technology of stress cell systems to accommodate gallium doped germanium photoconductors is presented. The novel feature of the cell is the inclusion of a miniaturized spring calibrated in situ. Stress control measurements were made at 4.2 K by optical and electrical photoconductor characterization.
Photogenerated current at 77K, when the transparent gate of an Hgl-xCdxTe(x=0.29) and InSb p-channel MISFETs is illuminated with infrared radiation, have been evaluated theoretically as a function of gate voltage. To process of excitation are considered, namely, an electron-hole pair generation across the bandgap in the depletion layer of the field induced junction and an electron excitation through interface states at the semi-conductor-SiO2 interface. The photocurrent is primarily due to the later process. For sake of comparison, the drain-source current without illumination has also been calculated as function of gate voltage.
The first measurements are those of Rubens and Czerny on NaCl, KBr, KCl and NaI at the beginning of this century, and indeed Rubens used a simplified kind of Fourier transform spectroscopy at these earliest times! The review will discuss different models which are now used and some applications. Special care will be given to small effects in reststrahl spectra which are expected from divergence of polarization at the surface.
This paper is a review of current developments in new optical materials based on a survey of the recent literature. Rapid advances are taking place in the fields of passive and active optical materials. Among the former are new optical fibers and refractive materials suitable for excimer lasers. Among the latter are electrooptic crystals of many varieties including liquid crystals and molecular non-linear materials. Among the key application areas are optical fibers waveguides, optical storage, and optical data processing devices. Several examples of each of these new areas will be mentioned in the paper.
This review seeks to aid the choice of an infrared optical material for applications use by discussing the optical properties of halides, oxides, chalcogenides and semiconductors in relation to other physical properties. It is shown how this information can be utilised to enable a realistic choice of material to be made.
The effects of dispersion, angle of illumination and temperature in coated layers of infrared semiconductors (the IV-VI) and semiinsulators (the II-VI) are described. Examples are given of microcomputer calculations of these.
Molecular beam techniques have been used to produce optical thin films with a high resistance to laser induced damage at 10.6μm. Cross-sectional transmission electron micrographs XTEM demonstrate that the films have a polycrystalline columnar morphology with grain size dependent on deposition temperature and film material, but in the range 250-1000A for ZnSe. SiOx films produced by RF sputtering in ultra clean environments are amorphous and featureless in cross section. A characteristic feature of all films so far produced in UHV is the complete absence of porosity. Interface perfection is high. The MBE techniques allow a high degree of control over the film deposition process and have the potential for allowing the growth of novel coating structures especially those based on graded index designs.
Theoritical analysis of high band gap Hgl-xCdxTe infrared absorption and consideration of the available metallurgical processes show the ability of this material to give rise to optical waveguides exhibiting characteristics equivalent or better than classical III V in-frared waveguides at 10.6 μm. The E.D.R.I. process (Isothermal Evaporation Diffusion) has been used to grow HgCdTe layer on CdTe substrates. The Hgl-xCdxTe (x = 0.5) source material has been obtained by the Travelling Heater Method. Exceptionally transparent material at 10.6 pm is obtained for Cd composition x greater than 0.5. The E.D.R.I. process produces graded composition layer ranging from x = 0.55 at the surface to x = 1 in the substrate, giving rise to highly transparent graded index waveguides. When a 10.6 μm beam is coupled by a high index Germanium prism with the waveguide modes, the totally reflected light exhibits m-lines at specific angles from which the effective indices of the waveguide modes are deduced. Then an inverse W.K.B. computation leads to the refractive index profile of the structure. The comparison with the Cadmium ratio obtained with the electron microprobe gives the relation between refractive index and Cadmium concentration. The propagation of a 10.6 μm wave exhibits an exceptionnally low attenuation (< 0.5 dB/cm) on all TE modes, even those of high order.
Proc. SPIE 0588, Engineering Development For Reproducible Volume Production Of Cadmium Sulfide (CdS) Waveplates And Their Applications In Infrared Laser Systems, 0000 (7 July 1986); doi: 10.1117/12.951779
Single crystal cadmium sulfide waveplates have several attractive technical properties to be used as phase retarders in various low power infrared laser systems for defense and aerospace industries. CdS waveplates can be used with CO2, CO, and HF/DF laser systems. Their advantages are power handling capacity to the 100 watt CW range, low insertion loss, ease of alignment due to visible transparency and no beam off-set when inserted in the laser system. Cadmium sulfide waveplates must be manufactured to a high degree of precision in thickness, parallelism and flatness. Due to the crystalline structure, and the soft and fragile nature of the CdS material, volume production of CdS waveplates is a difficult engineering, high technology problem. Currently, these waveplates are manufactured in small quantities. To meet the growing demand for CdS waveplates for infrared laser systems used in defense and aerospace industries, we conducted several engineering and technological experiments exploring new processes and techniques of manufacture to produce waveplates in larger quantity and to study the performance of these waveplates. This paper describes the important technical properties of single crystal cadmium sulfide as a waveplate material, the problems associated with waveplate manufacture and the technological developments made in the techniques of manufacture of these waveplates.
Polycrystalline MgAl204 which is transparent in the infrared spectral regions can be achieved by hot pressing of high activity powders. Fine, homogeneous and high purity MgAl204 powders were obtained by metal alkoxide-hydrolysis method. Three processes for powder preparation have been approached, namely, (1) conventional alkoxide-hydrolysis process, (2) sol-gel process and (3) diluted-sol drying process. The last process was the most attractive one, as it is easier to control the powder morphology and takes less time to prepare. Drying process affects the characteristics of the powders significantly. The morphology of spray-dried powders are thin-wall hollow spheres of uniform size, while those of freeze-dried powders show agglomerated lump. Spray-dried powders possess higher sinterability and the disks hot preesed from these powders show higher infrared transparency. That of the hot pressed spinel samples was further improved by heat treatment and optical polishing.
Calcium lanthanum sulphide has been identified as a material worthy of detailed investigation for infrared window applications. Sintering of a pure sulphide powder to closed porosity followed by hot isostatic pressing to achieve full density appears to be the most promising synthesis route. In the present work an evaporative decomposition of solution (EDS) powder synthesis technique has been utilised. A mixed nitrate solution was sprayed through a hot furnace to yield mixed oxide precursor powder which was collected at the end of the furnace. This powder was then fired in H2S gas to synthesise a fine powder of calcium lanthanum sulphide raw material for ceramics processing. The evolution of the powder synthesis and ceramic processing techniques has enabled a continued improvement in ceramic quality. In 1981 very dark almost black CaLa2S4 not transmitting in the IR was typical of the material being synthesised by hot pressing. By 1983 a very dark brown CaLa2S4 partially transmitting in the visible and IR but showing extrinsic SO3 and SO4 absorptions was synthesised by hot pressing followed by annealing in H2S. In 1985 extrinsic absorption free lemon yellow coloured CaS45La2S355 (mole%) material transmitting in the visible and IR but showing some visible and near IR scatter has been synthesised by sintering in H2S followed by hot isostatic pressing (HIP) in argon.
Although reflecting coatings are very common components they must be used sometimes with care in special applications. The aim of this paper is to discuss 2 kinds of problems met in using dielectric mirrors : - the relative phase shift between the p and s polarization components of the incident light - the difficulty to get an high reflectance over a large spectral bandwidth