The results of investigation of planar photodiodes (PDs) in a focal plane array (FPA) based on a heteroepitaxial InGaAs/InP structure are reported. The FPA has a size of 320 × 256 elements with a ...pitch of 30 μm, which are hybridized with various ROIC readout circuits. It is demonstrated that the PD reverse bias should be no lower than 2 V in order to suppress the FPA intercoupling at the room temperature. It is found that the dark current may be reduced considerably by cooling the FPA to–20°С with a two-stage thermoelectric cooler. The best average room-temperature dark current over the FPA planar photodiodes is 0.22 pA at an optimum PD bias of–2.4 V.
Principles of an analytical system of physical design of avalanche heterophotodiodes with separate regions of absorption and multiplication (AHPD with SRAM) are presented. The system is based on ...analytical expressions for the field of the avalanche breakdown of the
p–n
heterostructure and the interband tunnel current in it. This current determines the minimum noise level in the AHPD with SRAM based on direct band semiconductors. The considered method strongly facilitates optimization of the doping levels of the heterostructure layers and their thicknesses. In addition, it gives significantly more pronounced physical content to the optimization process.
The analysis of the current state of solid photoelectronics for thermal imaging and thermal direction-finding equipment of new generation is performed. The results of the latest development of ...photoelectronic modules for thermal imaging and thermal direction-finding in the spectral bands 1–3, 3–5 and 8‒12 μm, as well as for ultraviolet range are presented. The main physical and technological problems of the design of photoelectronic modules as well as production of photosensitive materials for them are considered. A forecast of the directions of development is presented.
The design of a 14-bit delta-sigma analog-to-digital converter (ADC) with pipelined readout is considered. Basic concepts of the design of array photodetectors of the infrared (IR) range with an ADC ...in the accumulating cell are analyzed. The presence of an ADC in the readout large-scale integrated circuit (LSIC) cell provides an opportunity to increase the accumulation time by more than an order of magnitude and improve the threshold characteristics. A method for optimization of the ADC area by using an LFSR counter operating in two modes (digital code generation and serial readout) is proposed.
A technique for measuring photoelectric parameters of focal plane arrays (FPAs) with time delay and integration (TDI) operation mode without optical-mechanical scanning is presented. A feature of the ...FPA is the presence of disconnectable high-pass filters in the input cells of the large-scale integration circuit (LSI), which makes it possible to subtract the inconclusive constant component of the signal. A blackbody (BB) with modulator is used as an optical signal source. The criterion of selection of the modulation frequency is the TDI period and the amplitude–frequency characteristics of the FPA. In order to perform correct measurements of signal values, parameters of a nonrecursive TDI filter are calculated. Values of the FPA noise are obtained by subtracting the periodic amplitude modulation. The dependence of background irradiances on the photodetector is calculated and the dependence of the FPA noise on the background temperature is constructed. The internal FPA noise is calculated and numerical values of measured parameters are presented.
The absorption coefficient of HgCdTe structures grown by the methods of liquid-phase epitaxy (LPE) and metalorganic chemical vapor deposition (MOCVD) is studied and calculated. The experimental data ...are compared to a theoretical absorption spectrum model, which is based on the fundamental absorption effect and the general theory of direct interband optical transitions, as well as other empirical dependences. The Fermi level shift in the studied HgCdTe structures and the slope of experimental absorption characteristics are calculated.
The results of measurements of the root-mean-square (rms) surface roughness of CdZnTe substrates by confocal microscopy (CM), atomic force microscopy (AFM), and X-ray reflectometry (XRR) are ...compared. It is determined that CM yields the highest rms roughness values, AFM assumes an intermediate position, and XRR measurements produce results that are an order of magnitude lower than those obtained with the use of the other two techniques. It is demonstrated that CM rms roughness values depend to a considerable extent on the type of the microscope objective used in experiments. Probable reasons for the discrepancy between the obtained results are discussed.
The theory making it possible to rather accurately predict a complete set of characteristics (signals, noises, and photoelectric parameters) inherent to all components of the photodiode-based focal ...plane array (FPA) under design and optimize its parameters has been developed. The theory relies on a new approach to the determination of FPA irradiance, which ensures its calculations at any shape of the diaphragm in the light-insulating shield. Both staring and scanning FPAs, the latter of which operate under the condition of time delay and accumulation, are discussed. The theory has been verified using a 320 × 256 FPA. The calculated dependences of the signals and noises of photoelectric components are compared with the experimental values obtained at different accumulation times and background irradiation temperatures. The theoretical data are revealed to be in complete agreement with the experiment, confirming the model validity. The theory will be undoubtedly useful for designers, manufacturers, and users of FPAs. The model can easily be extended to systems with FPAs.
SWIR ADP 320 × 256 FPAs based on
p
–
i
–
n
photodiodes in InGaAs heterostructures have been developed and investigated. The typical InGaAs/InP PIN heterostructures are formed by Metal Organic Vapor ...Phase Epitaxy (MOVPE) on
n
+
type InP substrates. The InGaAs/InP PIN photodiodes performance have been estimated by measuring current-voltage characteristics. APD arrays are designed using a mesa-passivated avalanche photodiode device array of
p
–
i
–
n
junctions in heterostructure with common absorption and multiplication regions. The optimal operating point for managing avalanche application depended on various factors has been started at 15 V bias and the multiplication coefficient was of 2–4.
Using an analytical model of the avalanche heterophotodiode (AHPhD), principles of selection of its optimal structure are given. The model is based on analytical expressions for the field of the ...avalanche breakdown of the
p
–
n
heterostructure and the interband tunnel current in it, which determines the minimum noise level in the AHPhDs based on direct bandgap semiconductors. To reduce the tunnel current, it is necessary to use a structure with separated absorption and multiplication regions. This approach allows one to analytically determine parameters of the structure in which the latter is implemented. In addition, it enables one to analytically determine such parameters and structures of “low–high–low” type that simultaneously provide both the minimum tunnel current and the minimum avalanche noise factor.
