MCT was independently synthesized in Soviet Union one year later than in UK. MCT investigations and technology
development virtually started from the material origin. Main milestones of this way from early days to the present are
reviewed. Deep researches and MCT based device development spring from the projects which Scientific Research Institute
of Applied Physics (now ORION Research and Production Association) charged with in 1969. Gradual material,
photoresistor and photodiode technology developments were carried out in 1970-1990 and resulted in n-type single crystals
MCT industrial production mastery, photoconductive detectors series up to 200 elements and high frequency heterodyne
detectors production. New generation devices - focal plane arrays and MCT epitaxial technology were developed
in 1980-2000. MCT FPA and heteroepitaxial technology enhancement since 2000 led to production of the family of long
linear and staring second generation arrays in various formats and package configurations. Third generation devices pointed
on advanced MCT heteroepitaxial technologies and new type photosensitive structures creation are under development.
Original investigations of some interesting phenomena in MCT and device structures such as injection heat transfer and
negative differential conductance in MCT diodes, metal-tunnel transparent insulator structures are also presented.
Transmittance spectra of epitaxial layers grown on the basis of mercury and cadmium telluride (MCT) alloys have been
measured within the wavelength number range of (5000 cm-1<ν<500 cm-1). P-type epitaxial layers were grown both by
liquid-phase epitaxy method (LPE) on CdZnTe substrates and molecular-beam epitaxy (MBE) on GaAs substrates. The
MCT layer parameters such as epitaxial layer thickness d, cutoff wavelength λ05, composition x were calculated from the
spectra.
JR transmittance spectra simulation method was developed to determine the semiconductor multilayer structures
characteristics. Fourier Transform (FT) method was suggested to determine the thickness of MCT epitaxial layers.
Parameter calculations were carried out for two types of filtering devices in one of which the phenomenon of the total internal reflection was used and in the other the multibeam interference was used for the optical radiation filtering. It is expected that these devices may be suitable for imagery of objects in the given narrow spectral bands - spectral imaging (SI).
LWIR staring 384x288 focal plane array (FPA) has been developed and investigated. FPAs are manufactured on the basis 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 readout integrated circuit (ROIC). The photodiodes array pitch in each direction is 28 μm. ROIC performs the photocurrents integration during row period, signals multiplexing in two output channels from the focal plane. MCT photovoltaic array and ROIC are bonded by indium bumps. This photosensitive assembly is packaged in vacuum metal encapsulation and cooled down to temperature 80 K. Average detectivity was of 4.4.1010 W-1.cm.Hz1/2 for FPA cutoff wavelength of 10.7 μm. Test IR system on the basis of FPA was developed to obtain thermal images in real time mode at frame frequency 50 Hz. Test IR system performs two-point correction and defective elements replacement.
The optical filter for 8-12 microns spectral range on the base of MCT epilayer grown by Metal Organic Chemical Vapor Deposition (MOCVD) has been investigated. The CdTe mole fraction in CdxHg1-xTe equals x=0.24. The single-layer antireflection coatings for 10 μm peak wavelength have been deposed on the both sides of the filter. Transmission in 8-12 μm spectral range exceeds 70%. Transmission at 7 μm is of 40%, at 6 μm-10%, at 5 μm-less than 2%.
The results of development researches and tests of the 4x288 focal plane array (FPA) for a spectral range 8-12 microns are given. The cooled photoreception module of the FPA represents hybrid assembly of a matrix photosensitive element based on liquid phase epitaxy (LPE) mercury-cadmium-telluride (MCT) photodiodes and cooled silicon readout integrated circuit (ROIC). Connection of the MCT and ROIC is carried out by means of In bumps. Cooled silicon readout circuits have been made by n-MOS technology with no TDI stages at focal plane. For 11.5 μm cutoff wavelength detectivity is higher then 1x1011 cmW-1Hz1/2 for 4x288 FPA with four TDI elements.
Charge carriers diffusion length needs to be exactly calculated in p-type HgCdTe (MCT) epitaxial layers to design focal plane array (FPA) with small crosstalk and high performance. The mathematical model and the computing program to determine the minority carriers diffusion length from experimental data of photodiode spatial signal response versus the optical spot position along the pixel have been developed. The correlation of diffusion length data with other methods data has been analyzed.
Different current mechanisms in HdCdTe p-n junctions have been analyzed. Current-voltage characteristics of photodiodes in HdCdTe epitaxial layers formed by different epitaxial methods are measured and simulated. The numerical simulation of photodiodes current-voltage characteristics allows to evaluate HdCdTe material parameters and improve Focal Plane Arrays technology.
MWIR 128x128 Focal Plane Array (FPA) performance has been investigated. FPA has been fabricated on the base of HgCdTe active layers grown on (111)B GaAs substrate by Metal Organic Chemical Vapor Deposition (MOCVD). Histograms and diagrams of photodiodes current, responsivity and detectivity have been plotted for FPA with cutoff value 5,1μm at T=200K.
xResults of studying photodetectors (FD) and photodetecting assemblies (PDA) provided for receiving lased radiation in 0.2÷12 μm range are given in the paper. A possibility of using low-frequency CdxHg1-xTe photoresistors for recording CO2-laser pulses of up to 20 ns duration is discussed.
A FPA architecture and technology developed by RD&P Center ORION based on planar HgCdTe photodiode arrays and cooled silicon integrated readout circuits is presented. Photovoltaic detectors array made on mercury cadmium telluride (MCT) liquid phase epitaxy (LPE) layer and silicon readout circuits are linked by indium bumps on sapphire interconnection substrate. Cooled silicon readout circuits have been made by n-MOS technology with no TDI stages at focal plane. For 8-12 μm wavelength range detectivity is (5-10)×1010 cmW-1Hz1/2 for 2x256 FPA with two TDI elements.
Results of studying photodetectors (FD) and photodetecting assemblies (PDA) provided for receiving lased radiation in the 0.2÷12 tm range are given in the paper. A possibility of using low-frequency CdXHgI-X Te photoresistors for recording CO2 — laser pulses of up to 20 ns duration is discussed. Photodiodes and photoresistors are compared when operating in an optical detector with heterodyning.
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.
Single element and linear array photodetectors operating in heterodyne mode for CO2 laser radiation detection have been developed and investigated. P-type mercury cadmium telluride (MCT) crystal with x=0.21 composition and hole concentration 1x1016 cm-3 at T=77K were used as substrates. The p-n junctions in p-type MCT were formed by ion implantation. Detector was packaged in metal-glass dewar together with preamplifier. Cooling was performed by liquid nitrogen. Single-element heterodyne detector with p- n junction area 300X300 micrometers operates at frequencies up to 100 MHz. The noise equivalent power (NEP) at 10,6 micrometers wavelength is equal to 5x1020 W/Hz for an applied local oscillator power 0,5 mW. 10-element photodiode linear array heterodyne detector been developed and investigated.
Crosstalk in 32 X 32 and 128 X 128 HgCdTe staring focal plane arrays consisting of HgCdTe photodiode array bonded with silicon MOS-multiplexer by indium bumps have been investigated. The experimental results of crosstalk caused by the diffusion of photogenerated carriers, inverse surface layers and photoresistance effect in HgCdTe substrate are presented. The influence of drain-source leakage in multiplexer switching transistors on crosstalk is discussed.
Current-voltage characteristics of LN2 cooled MCT p-n tunnel junctions have been investigated. The negative differential conductance takes place at negative total current due to photocurrent bias. This gives possibility of current oscillation without external electric power.
Cadmium mercury telluride (MCT) photodiodes stability has been investigated. Possible reasons of photodiodes performances degradation are analyzed. High temporal and thermal stability at storage temperature up to 70 degree(s)C of ion implanted MCT photovoltaic detectors is shown.
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 method of IR detector sensitivity spatial distribution restoring from the experimentally measured photosignal dependence versus optical spot position and known optical spot spread function is developed and experimentally investigated.
IR imager have been developed and investigated. IR imager consists of mercury cadmium telluride 128 X 128 staring focal plane array bonded by indium bumps with silicon MOS- multiplexer, split-Stirling cooler, electronic signal processor. Noise equivalent temperature difference NETD is less than 0.1 K.
Using Fourier Transform Spectroscopy (FTS), we have measured HgCdTe diodes and resistors photoresponse at wavelengths below the fundamental absorption edge in this semiconductor. This study is inherent to FTS photoresponse and is performed by the long wavelength radiation modulation of the short wavelength photocurrent. Possible physical mechanisms of such modulation are discussed.
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