A numerical model of the current noise spectral density in elements of infrared focal plane array based on HgCdTe
photodiodes has been developed. Model is based on Langevine method and applied to the photodiode with p+-n-junction
and base of finite length d. Dominated dark current diffusion mechanism and random nature of thermal generationrecombination
and scattering processes determined the diffusion current fluctuations has been taken into account.
The model main peculiar properties are the stochastic boundary conditions on the interface between the depletion and
quasineutral regions. Current noise spectral density of the diode with thin base d < Lp, where Lp is the hole diffusion
length in n-region, has been calculated. In thin base diodes with blocking contact to substrate, in which recombination
velocity S = 0, a noise suppression effect is revealed. At noticeable reverse junction biases |qV| > 3kT the diffusion current
noise suppression is to be observed in whole frequency band ωtfl
<< 1, where tfl is the hole flight time through the
depletion region. In this case the diffusion current noise spectral density is less than in diodes with thick base (d >> Lp)
by a factor th(d/Lp). At slight biases |qV| < 3kT the diffusion current noise suppression occurs only in limited frequency
band ωτ < 1, where τ is the minority carriers lifetime. At high frequencies ωτ >> 1 diffusion current noise comes out
of fluctuations caused by scattering processes and is independent on the diode structure. Photocurrent noise spectral
density has been calculated too. Model developed is useful for the photodiode elements and arrays optimization.
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.
Infrared second generation photodetectors developments have been carried out in RD&P Center "Orion" for creation short
wavelength IR (SWIR, 1 to 3μm), medium wavelength IR (MWIR, 3 to 5 μm) and long wavelength IR (LWIR, 8 to 1 μm) on the
base of lead chalcogenides (PbS, PbSe), indium antimonide (InSb) and mercury cadmium telluride (CdHg1Te). Performance
and operational functionality of 2xl28 (PbS, PbSe), 256x256 (InSb), and 2x256, 4x288 256x256, 384x288, 768x576 (MCT) focal
plane arrays (FPA) are specified. Requirements to the FPA for main directions of thermovision systems applications are given.
Indium antimonide MWIR Focal Plane Array (FPA) have been developed and investigated. FPA consists of
two dimensional arrays of InSb photodiodes bonded by indium bumps with CMOS-multiplexer and LN2 cryocooler.
Noise equivalent power NEP≈1×10-12 W/pixel and dynamic range 60÷70 dB at frame frequency 250 Hz.
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 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.
Indium antimonide MWIR Focal Plane Array (FPA) have been developed and investigated. FPA consists of two dimensional anys of InSb photodiodes bonded by indium bumps with CMOS-multiplexer and Split-Stirling cooler. Noise equivalent power NEP≈7•10-13 W/pixel and dynamic range 60÷70 dB at frame frequency (800÷1000) Hz.
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.
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.
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