Molecular beam epitaxy has been used for the growth of Hg1-xCdxTe layers (x = 0.30 - 0.34) on Si(310) substrates. The
grown structures were characterized by Hall measurements for carrier density and mobility. The densities of stacking
faults, threading dislocations, antiphase boundaries and macroscopic V-defects were determined by selective chemical
etching. The 128 x 128 photodiode array with wavelength cut-off λ1/2(77K) = 4.07 μm was fabricated with good
photoelectric parameters.
The measurement signal (S) to noise (N) ratio (S/N) of novel 128×128 FPA in temperature range 77 -130K was carried
out. FPA for spectral range 8-12 μm was fabricated by B+ implantation process into graded MCT P-p heterojunction with potential barrier. MCT P-p heterojunction with specific MCT composition throughout the thickness was grown by MBE
on GaAs substrate by ellipsometric control in situ. The potential barrier was determined by the difference of MCT
composition at absorber and p-n junction location layers and equal to ΔXCdTe = 0,025. It was shown that based on P-p
heterojunction FPA operated temperature and wavelength increases over routine one without P-p heterojunction.
Keywords: graded gap layers, heterojunction, MCT, photodiodes, FPA.
Ultimate performance small-pitched infrared focal plane arrays (FPA) are of the great interest for development and production of state-of-the-art special and common use thermal imagers. Novel MBE-grown Hg1-xCdxTe/CdZnTe/GaAs heterostructures (MCT/CZT on GaAs HS) are considered perspective for implementation of sophisticated FPA concepts including multi-color and HOT (high operating temperature). Performance of MWIR and LWIR photoconductive (PC) and photovoltaic (PV) infrared detectors fabricated on the base of a. m. heterostructures are presented. The main feature of developed technology is formation of multi-layer device structure in single MBE growth run with precise control of thickness and alloy composition "x" across individual layers and hence throughout heterostructure. Flexible HS design results in half-finished products of PC and PV detectors with optimized parameters of absorber and perfect interfaces between absorber and blocking layers providing effective suppression of surface recombination and surface leakage currents. Giant peak responsivity RV (λco=10.5 μm, 500 K, 1200 Hz) over 6,0×105 V/W was reached on LWIR PC. Average values D* = 1.8×1011 cmHz1/2W-1 and NEDT = 9 mκ were measured on 4×288 PV FPA with λco = 11.2 μm at T=78 K just as 23 mK and 19 mκ on 320×256(240) PV FPA with λco = 5.5 and λco = 10.2 μm at T=78 K.
In the paper experimental results on boron implantation of the CdxHg1-xTe epilayers with various composition near surface of the material are discussed. The electron concentration in the surface layer after irradiation vs irradiation dose and ion energy are investigated for range of doses 1011 - 3•1015 cm-2 and energies of 20 - 150 keV. Also the results of the electrical active defects distribution measurement, carried out by differential Hall method, after boron implantation are represented. Consideration of the received data shows, that composition gradient influence mainly on the various dynamics of accumulation of electric active radiation defects. The electric active defects distribution analysis shows, that the other factors are negligible.
The electro-physical and photo-electrical properties of the HgCdTe/SiO2/Si3N4 and HgCdTe/anodic-oxide film MIS structures is experimentally studied. The heteroepitaxial graded-band films Hg0.78Cd0.22Te were produced on the GaAs substrates by molecular-beam epitaxy. It was established of features of electrical properties were related with conduction type of the semiconductor and to the presence of near-surface graded-band layers. The test measurements of the electro-physical and photoelectric performances of MIS-structures in base of graded-band HgCdTe are held and the following parameters are found: resistances of volume, voltage of flat bands, densities of mobile and fixed charges, spectrums of surface states. It is shown that low-temperature double insulator SiO2/Si3N4 is perspective for passivation of surface of focal plane arrays in base of HgCdTe-photodiodes.
CdTe and HgCdTe layers were grown by MBE on GaAs(310) and Si(310) substrates. The dependences of microrelief height and macroscopic defects densities on the growth conditions of CdTe layer are plotted. CdTe buffer layers with the average height of surface relief of 2 nm are obtained. HgCdTe layers on GaAs(310) substrates with V-shaped defects density of 200-300 cm-2 were grown. When Si(310) substrates are used, the boundaries between antiphase domains are an additional reason for formation of V-shaped defects. It is shown, that the optimization of surface preparation processes and the growth conditions allows to grow one-domain films of CdTe buffer layers on Si(310) substrates and to lower the density of V-shaped defects.
Compact small-pitched infrared focal plane arrays (FPA) having ultimate performance are of the great interest for development and production of state-of-the-art special and common use thermal imaging systems lighter in weight and with lower energy consumption. Novel MBE-grown Hg1-xCdxTe epitaxial multi-layer structures are considered perspective for manufacturing of such FPA. Objective of the present work was to examine the impact of small-pitched Long-Wave Infrared (LWIR) Hg1-xCdxTe photoconductor device performance on variation of background flux density. Peak wavelength λp was ranged from 10.5 to 11.5 μm at 78-100 K. High performance small active area photoconductors based on MBE-grown multi-layer structures consisting of homogeneous narrow-gap n-Hg1-xCdxTe absorbing layer (n-absorber) both side blocked by thin graded-gap Hg1-xCdxTe layers have been fabricated and examined. Availability of innovative Hg1-xCdxTe epitaxial material (half-finished products of photoconductors - three-layer sensitive structures grown by MBE in single run) gives opportunity to manufacture and offer versatile detectors with flexible tuning of electro-optical parameters. Multi-element (2 x 32=64 elements) Hg1-xCdxTe photoconductors with pixel's active area size 30 μm x 30 μm and pitch 45 µm were tested. Electro-optical measurements have shown improved value of peak responsivity and detectivity close to theoretically predicted for model photoconductor.
High performance large active area photoconductors based on MBE-grown multi-layer structures consist of homogeneous narrow-gap n-Hg1-xCdxTe absorbing layer (n-absorber) blocked by thin adjacent graded-gap Hg1-xCdxTe layers have been fabricated and examined. Large active area (from 0.25 mm x 0.25 mm to 2.25 mm x 2.25 mm) Hg1-xCdxTe photoconductors with improved responsivity in Mid-Wave 3.0-5.5 μm (MWIR); Long-Wave 8-14 μm (LWIR) and Very Long-Wave 14-20 μm (VLWIR) infrared spectral ranges are very attractive for use in state-of-the art IR imaging, analytical and spectroscopic equipment. Synergy of advanced Hg1-xCdxTe detectors with IR-fiber optics, especially based on polycrystalline infrared (PIR-) fiber (4-18 μm) cables and bundles, provides above mentioned equipment with qualitatively new possibility like as remote probing of the objects which are difficult to access or beyond direct optical access. Availability of innovative Hg1-xCdxTe epitaxial material (half-finished products of photoconductors - three-layer sensitive structures grown by MBE in single run) open perspective to manufacture and offer improved detectors for much number of applications. Low temperature MBE growth technique provides better tuning of detectors' spectral responsivity curves to the ordered spectral ranges. Measurements performed on fabricated photoconductors showed significantly increased value of peak responsivity and high level of detectivity.
MCT 2×64 and 4×288 linear arrays with silicon readouts were designed, manufactured and tested. (013) MCT MBE layers were grown on GaAs substrates with ZnTe and CdTe buffer layers. 2×64 arrays were also manufactured on the base of LPE layers on CdZnTe (111) substrates. 50×55 and ≈30×30 μm area n-p-type photodiodes were formed by 50 ÷ 120 keV boron implantation. The dark currents at V ≈ 100 mV reversed biased diodes used in arrays with cutoff wavelength λco ≈ 10.0 - 12.2 μm were within 15 - 50 nA and zero bias resistance-area products were within R0A ≈ 5 ÷ 20 Ohm×cm2. Designed silicon readouts with skimming and partitioning functions were manufactured by n-channel MOS technology with buried or surface channel CCD register. For achievement with the silicon readouts the deselection function, the “composite” technology approach was considered. In this case both the technology of n-channel CCD and CMOS technology were applied, which allow to weaken considerably the technological design rules for realization of 288×4 readouts with deselection of “dead” elements. It is shown that 2.5 μm design rules for CCD and 2.0 design rules for CMOS technologies allow to realize most of the functions needed for 288×4 MCT array operation with deselection function. Before hybridisation the parameters of MCT linear arrays and Si readouts were tested separately. HgCdTe arrays and Si readouts were hybridised by cold welding In bumps technology. In dependence of FOV with skimming mode used for integration time of 8 - 20 μs detectivities within D*λ (0.4 - 1.7)×1011 cm×Hz1/2/W were achieved in dependence of the array format. Dark carrier transport mechanisms in MCT diodes were calculated and compared with experimental data.
The surface microrelief of CdHgTe layers grown by molecular-beam epitaxy (MBE) method has been studied by means of atomic-force microscopy. A periodic surface microrelief in the form of an ordered system of extended waves with the characteristic period 0.1-0.2 μm has been detected on epilayers grown at increased temperatures. Angular dependencies of the conductivity at 77 K have been measured and the conductivity anisotropy has been detected with a minimum in the direction transverse to microrelief waves. A feature of the transmission system and the spectrum change after film annealing are observed. It is assumed that walls growing in the direction from the substrate to the surface are formed under microrelief waves slopes. Such structure can cause the observed feature of the transmission spectrum if the adjacent walls have different composition. In this work a calculation of spectral characteristics taking into account the influence of variable-gap composition and nonuniformity of the composition through the depth has been carried out.
The first results on a radiation stability investigation of mercury cadmium telluride (MCT) films, grown by molecular beam epitaxy (MBE) are represented. The samples were irradiated by high energy electron beams and gamma rays. Electrophysical and photoelectric parameters of MCT epilayers were measured. Volume material was measured too for the checking with MBE-grown one. MBE epifilms were irradiated on a pulsed electron accelerator with electron energy 1-2 MeV and current density less than 1 μA/cm2 for several fluences. Also MCT epitaxial heterostructures were irradiated by Co60 gamma rays. The same experiments were carried out for volume material. The analysis of dependence of Hall coefficient and conductivity from temperature and magnetic field (B) for p- and n- type samples was made. The irradiation of epilayers and volume MCT in the investigated range of irradiation fluences does not give both creation of electrical active damages in high concentrations and reconstruction of initial defects. Thus, MBE films of MCT have the high radiation stability to an electron and gamma irradiation. The obtained first results allow us to speak about high performance of explored MCT epilayers.
View of basic and specific physical and chemical features of growth and defect formation in mercury cadmium telluride (MCT) heterostructures (HS's) on GaAs substrates by molecular beam epitaxy (MBE) was made. On the basis of this knowledge a new generation of ultra high vacuum set, ultra-fast ellipsometer of high accuracy and automatic system for control of technological processes was produced for reproducibility of MCT Hs's growth on substrates up to 4" in diameter. The development of industrially oriented technolgoy of MCT HS's growth by MBE on GaAs substrates 2" in diameter and without intentional doping is presented. The electrical characteristics of n-type and p-type of MCT HS's and uniformity of MCT composition over the surface area are excellent. The residual donor and acceptor centres are supposed as hypothetically tellurium atoms in metallic sublattice ("antisite" tellurium) and double-ionised mercury vacancies. The technology of fabricating focal plane arrays is developed. The high quality characteristics of infrared detectors conductance and diode mode are measured. Calculations of detector parameters predicted the improvement in serial resistance and detectivity of infrared diode detectors based on MCT heterostructures with graded composition throughout the thickness.
x4×288 heteroepitaxial mercury-cadmium telluride (MCT) linear arrays for long wavelength infrared (LWIR) applications with 28×25 micron diodes and charge coupled devices (CCD) silicon readouts were designed, manufactured and tested. MCT heteroepitaxial layers were grown by MBE technology on (013) GaAs substrates with CdZnTe buffer layers and have cutoff wavelength λco ≈ 11.8 μm at T = 78 K. To decrease the surface influence of the carriers recombination processes the layers with composition changes and its increase both toward the surface and HgCdTe/CdZnTe boundary were grown. Silicon read-outs with CCD multiplexers with input direct injection circuits were designed, manufactured and tested. The testing procedure to qualify read-out integrated circuits (ROICs) on wafer level at T = 300 K was worked out. The silicon read-outs for 4×288 arrays, with skimming and partitioning functions included were manufactured by n-channel MOS technology with buried or surface channel CCD register. Designed CCD readouts are driven with four- or two-phase clock pulses. The HgCdTe arrays and Si CCD readouts were hybridized by cold welding indium bumps technology. With skimming mode used for 4×288 MCT n-p-junctions, the detectivity was about (formula available in paper) for background temperature Tb = 295 K.
Molecular beam epitaxy of MCT makes it possible to dissolve the problems of producing MCT heteroepitaxial structures with uniformity parameters on the large size alternative substrates for IR PD of existent and new generation and the growing of MCT layers on Si -substrates. The information about characteristics of geteroepitaxial structures on GaAs-substrates, a new generation equipment for controlled growing of MCT layers by MBE and technological conditions allowed to grow the epitaxial buffer CdTe layers on Si-substrates are represented in this work.
A complete technological cycle has been designed to produce photodetector arrays, which involves MBE growth of Hg1-xCdxTe (MCT) heteroepitaxial layers, fabrication of MCT-based photodetector structures, manufacture of silicon array multiplexers and hybrid assembly of a photodetector module consisting of a photodetector and multiplexer by means of indium micro bumps. Photoelectric parameters are given of photodetector array modules on the basis of photodiodes for the middle (3 - 3.5 μm) and far (8 - 12 μm) infrared ranges, operating at 78 - 80 K and 200 - 220 K temperatures.
New generation of ultra high vacuum set, ultra-fast ellipsometer of high accuracy and automatic system for control of technological processes was produced for reproducibility growth of mercury cadmium telluride (MCT) solid solution heterostructures (Hs's) by molecular beam epitaxy (MBE). This system allows to grow MCT HS's on substrate up to 4" in diameter and used for future development technology of growth on Si substrate. The development of industrially oriented growth MCT HS's MBE on GaAs 2" in diameter is presented. The electrical characteristics of n-type and p-type MCT HS's MBE and uniformity of MCT composition over the surface area is excellent and satisfied for fabricating multielements arrays of high quality infrared devices.
Dark carrier transport mechanisms in narrow-gap Hg1-xCdxTe multilayer structures and Pb1-zSnzTe/PbTe1-yS(Se)y heterojunctions at T~80 K for applications in IR arrays are analyzed and compared with homojunction mercury-cadmium telluride (MCT) photodiode characteristics in the temperature range T~70-150 K. In the analysis procedure two major current mechanisms were included into the current balance equations: trap-assisted tunneling (TAT) and Shockley-Reed-Hall (SRH) generation-recombination processes for a defect trap level. Other current mechanisms (e.g., band-to-band tunneling, bulk diffusion) were taken into account as additive contributions. For TAT the tunneling rate characteristics were calculated within the k-p-approximation. Using donor and acceptor concentrations, trap level energies and concentrations, and in-junction trap level lifetimes as fitting parameters, good agreement with experimental data for HgCdTe and PbSnTe heterojunction and homojunction diodes was obtained, which allows one to predict the diode parameters from the known material characteristics. Photodiode or array parameters itself, or with CCD readouts, or CCD readouts separately were tested to study the influence of readout cascade on the diodes' properties.
A technology was designed and the photodetector modules were manufactured for the 3 - 5 and 8 - 12 μm spectral range based on the Hg1-xCdxTe/GaAs heterostructures and GaAs/AlGaAs multiquantum well structures grown by the molecular beam epitaxy method. The photosensitive HgCdTe layers were grown on the GaAs substrates with the intermediate buffer layer of CdZnTe. To decrease the surface influence on the recombination processes graded gap HgCdTe layers with the increased to the surface composition were grown. A silicon multiplexer was designed and manufactured on the CMOS/CCD technology with frame rate 50 Hz. Hybrid assembly of the photodetectors array and the multiplexer was produced by the group cold welding on the indium bumps with control of the connection process. The manufactured 128 X 128 FPAs on the HgCdTe with the cut-off wavelength 6 μm and 8.7 μm had the NEDT value 0.02 K and 0.032 K, correspondingly, at operating temperature 78 K and frame rate 50 Hz. The photosensitive GaAs/AlGaAs multiquantum well structures were manufactured by the MBE method. It is shown that the designed technology allows to produce 128 X 128 photodetector arrays (λmax = 8 μm) with the NEDT value 0.021 K and 0.06 K at operating temperature 54 K and 65 K, correspondingly.
Mercury-Cadmium-Telluride (MCT) 2 X 64 linear arrays with silicon readouts were designed, manufactured and tested. NCT layers were grown by MBE method on (103) GaAs substrates with CdZnTe buffer layers. 50 X 50 mm n-p-type photodiodes were formed by 80 divided by 120 keV boron implantation. The dark current at 100 mV reversed biased diodes was within 15*30 nA and zero bias resistance-area product was within R0 approximately equals 20 divided by 50 Ohm X cm2. Silicon read-out circuits were designed, manufactured and tested. Read-outs with skimming and partitioning functions were manufactured by n-channel MOS technology with buried or surface channel CCD register. The parameters of LWIR MCT linear arrays with cutoff wavelength (lambda) co 10.0 divided by 12.2 micrometers and Si readouts were tested separately before hybridization. The HgCdTe arrays and Si readouts were hybridized by cold welding In bumps technology. With skimming mode used for integration time of 24-30 ms for such MCT n-p-junctions, the detectivity D*(lambda ) approximately equals 4 X 1010 cmXHz1/2/W. Dark carrier transport mechanisms in these diodes were calculated and compared with experimental data. Two major current mechanisms were included into the current balance equations: trap-assisted tunneling and Shockley-Reed-Hall generation-recombination processes via a defect trap level in the gap. Other current mechanisms (band-to-band tunneling, bulk diffusion) were taken into account as additive contributions. Tunneling rate characteristics were calculated within k-p approximation with the constant barrier electric field. Relatively good agreement with experimental data for diodes with large zero resistance-area products (R0A > 10 OhmXcm2) was obtained.
Two X sixty-four linear photodiode arrays on the base of HgCdTe MBE grown layers with CCD silicon readouts were designed, fabricated and tested. It is shown that detectivity for the given arrays even with skimming mode used for long integration times that is need for large square n-p-junctions used and cut-off wavelength of 12.2 micrometer was near the ultimate performance limit.
A technology was designed and the photodetector modules were manufactured for the 3 - 5 and 8 - 12 micrometer spectral range based on the Hg1-xCdxTe/GaAs heterostructures and GaAs/AlGaAs multiquantum well structures grown by the molecular beam epitaxy method. The photosensitive HgCdTe layers were grown on the GaAs substrates with the intermediate buffer layer of CdZnTe. To decrease the surface influence on the recombination processes graded gap HgCdTe layers with the increased to the surface composition were grown. A silicon multiplexer was designed and manufactured on the CMOS/CCD technology with frame rate 50 Hz. Hybrid assembly of the photodetectors array and the multiplexer was produced by the group cold welding on the indium bumps with control of the connection process. The manufactured 128 X 128 FPAs on the HgCdTe with the cut-off wavelength 6 micrometer and 8.7 micrometer had the NEDT value 0.02 K and 0.032 K, correspondingly, at operating temperature 78 K and frame rate 50 Hz. The photosensitive GaAs/AlGaAs multiquantum well structures were manufactured by the MBE method. It is shown that the designed technology allows to produce 128 X 128 photodetector arrays ((lambda) max equals 8 micrometer) with the NEDT value 0.021 K and 0.06 K at operating temperature 54 K and 65 K, correspondingly.
The molecular beam epitaxy (MBE) set-up with analytical control equipment of growth process was designed and fabricated for growing A2B6 compounds including the mercury-containing ones. A technology was elaborated for growing mercury-cadmium-telluride (MCT) solid solution heteroepitaxial structures (HS) by molecular beam epitaxy (MBE) method with a given variation of MCT composition throughout the thickness. HS's MCT MBE on CdZnTe/GaAs substrate with different variation composition in layers at MCT film interfaces were designing and growing. These structures were used for manufacture of high quality single, linear and array photoconductors (PC) and photodiodes (PD) operating at 77 K and 200 - 250 K temperature in the wavelength range of 3 - 5 micrometer and 8 - 12 micrometer, up and over 20 micrometer. Widegap layers at MCT film interfaces are used as passivating coating. Narrowgap layer at MCT film/CdZnTe buffer layers interface is used for decrease of PD series resistance. For decrease of dark currents of photodiodes array operating at 200 K HS MCT MBE were used with special composition distribution of composition throughout the thickness.
A technology was designed and the photodetector modules were manufactured for the 3-5 and 8-12 micrometers spectral range based on the Hg1-xCdxTe/GaAs heterostructures and GaAs/AlGaAs multiquantum well structures grown by the molecular beam epitaxy method. The photosensitive HgCdTe layers were grown on the GaAs substrates with the intermediate buffer layer of CdZnTe. To decrease the surface influence on the recombination processes graded gap HgCdTe layers with the increase to the surface composition were grown. A silicon multiplexer was designed and manufactured on the CMOS/CCD technology with frame rate 50 Hz. Hybrid assembly of the photodetectors array and the multiplexer was produced by the group cold welding on the indium bumps with control of the connection process. The manufactured 128 x 128 FPAs on the HgCdTe with the cut- off wavelength 6 micrometers and 8.7 micrometers had the NEDT value 0.02 K and 0.032 K, correspondingly, at operating temperature 78K and frame rate 50Hz. The photosensitive GaAs/AlGaAs multiquantum well structures were manufactured by the MBE method. It is shown that the designed technology allows to produce 129 x 128 photodetector arrays ((lambda) max=8 mum) with the NEDT value 0.021 K and 0.06 K at operating temperature of 54 K and 65 K, correspondingly.
For manufacture of focal plane arrays (FPA) the MBE grown heteroepitaxial structures GaAs/CdZnTe/CdHgTe with cut-off wavelength ((lambda) c) of 6.0 and 8.7 micrometers were used. The photosensitive CdHgTe layer was grown with special composition profile in depth being continuously controlled in the growth process. On these structures by the method of low temperature planar technology the 128x128 photodetector arrays were manufactured, including the ones with low series resistance for the far IR range. The read-out circuit was designed and silicon array multiplexers were manufactured CMOS technology with n- pocket. The read-out circuit allows to control the accumulation time at a fixed frame time. The technology of hybrid assembling with continuous control over cold welding on indium bumps was designed and the 128X128 FPAs were fabricated by means of this technology. The noise-equivalent difference of temperature (NEDT) value was 19.7 and 27.2 mK for modules with (lambda) c=6.0 micrometers and 8.7 micrometers correspondingly at the background temperature 77K. Using the IR camera the examples of IR images obtained by the fabricated FPAs with the 128x128 frame format are demonstrated.
The molecular beam epitaxy (MBE) set-up with analytical control equipment of growth process was designed and fabricated for growing A2B6 compounds including the mercury-containing ones. A technology was elaborated for growing mercury-cadmium-telluride (MCT) solid solution heteroepitaxial structures (HS) by molecular beam epitaxy (MBE) method with a given variation of MCT composition throughout the thickness. HS's MCT MBE on CdZnTe/GaAs substrate with different variation composition in layers at MCT film interfaces were designing and growing. These structures were used for manufacture of high quality single, linear and array photoconductors (PC) and photodiodes (PD) operating at 77K and 200-250K temperature wavelength range of 3-5 micrometers and 8-12$ mum, up and over 20micrometers . Widegap layers at MCT film interfaces are used as passivating coating. Narrowgap layer at MCT film/CdZnTe buffer layers interface is used for decrease of PD series resistance. For decrease of dark currents of photodiodes array operating at 200 K HS MCT MBE were used with special composition distribution of composition throughout the thickness.
LWIR staring at 384x288 focal plane array (FPA) have been developed and investigated. FPAs are manufactured on the base of mercury cadmium telluride epitaxial layers grown both by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE). 384x288 FPA consists of a MCT photodiodes array formed in the p-type layer by ion implantation and silicon MOS-multiplexer. The photodiodes array pitch in each direction is 35 micrometers . Multiplexer performs the photocurrents integration during line period, signals multiplexing and output form the focal plane. MCT photovoltaic array and MOS-multiplexer are bonded together by indium bumps. Sensitive unit is packaged in a metal dewar and cooled down to temperature 80 K. Average detectivity was more than 1.5x1010W-1cm/s-1/2 for FPA with cutoff wavelength of 11.9 micrometers at T=80K. Test IR system on the base of FPA was developed to obtain IR-images in real time mode with frame frequency 25 Hz. Test IR system performs two-point image correction and defective elements replacement.
LWIR staring 128 X 128 and 384 X 384 focal plane arrays (FPA) have been developed and investigated. FPAs have been manufactured on the base of mercury cadmium telluride epitaxial layers grown both by liquid phase epitaxy and molecular beam epitaxy. The photodiode array was bonded via the indium bumps to the silicon MOS-multiplexer, which ensure reading, integration and output of the photosignals from the focal plane. Performances of FPAs produced by these different epitaxial methods are analyzed.
The technology was developed and 128 X 128 LWIR FPA's based on HgCdTe epitaxial layers MBE-grown on GaAs substrates with cutoff wavelength (lambda) c equals 8 micrometer and 13 micrometer was fabricated. The photosensing layer HgCdTe was graded-gap layer with the higher content of Cd to boundaries of a layer. The manufactured LWIR FPA's had NETD 32 mK and 17 mK for (lambda) c equals 8 micrometer and 13 micrometer, correspondingly, at 295 K background and 80 K operation temperatures.
Heterostructures HgCdTe/CdTe/GaAs grown by molecular beam epitaxy were used for LWIR FPA fabrication. The technology was developed and 32 by 32 and 128 by 128 photodiode arrays with indium bumps of 15 micrometer height in each pixel were fabricated. Mean NEP is 1.7 by 10-13 W/Hz1/2 and 1.1 by 10-14 W/Hz1/2 for 128 by 128 photodiode arrays with (lambda) c value of 10.4 micrometer and 5.2 micrometer correspondently. The technology of hybrid assembling with continuous control of cold welding on the measuring stand was demonstrated on the example of 32 by 32 LWIR FPA. Mean NEP value of 5.4 by 10-14 W/Hz1/2 with (lambda) c equals 10.6 micrometer at 80 K operation were obtained. using an infrared camera system the infrared image was successfully demonstrated. The NETD value of 0.077 K was obtained under 293 K background condition.
We used the heterostructures of HgCdTe/CdZnTe/GaAs grown by molecular beam epitaxy for fabrication of photoconductor devices. The composition of MCT films throughout the thickness was controlled in situ by ellipsometry during the growth process. There were wide band gap layers at the interface and at the surface of the MCT films for decreasing the surface recombination which strongly influences on devices characteristics. The use of n-type material for LWIR photoconductors (77 K, the cutoff wavelength is more than 13 mkm) with good performance was demonstrated. The detectivity in maximum of wavelength dependence varies in interval (1.5 divided by 5)(DOT)1010 cmHz1/2 W-1. P-type material was used for MWIR photoconductors that operated at room and near room temperatures with the close to the theoretical value detectivity.
The results of MBE growth of CdHgTe epilayers and fabrication of photosensitive in 8 - 10 mkm region small p-n junctions using planar technology are presented. During MBE epitaxy the growing dynamic, composition and surface roughness were controlled in situ using build in high energy electron diffractometer and ellipsometer. Small area photosensitive diodes (50 X 70 mkm) were fabricated using planar technology and annealing under anodic oxide film. The measurements of V-I, spectral response and noise characteristics showed that the photodiodes on MCT epilayers grown by MBE have an acceptable parameters for fabrication of the linear and 2D photodiode arrays.
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