The paper reports on the photoelectrical performance of the long wavelength infrared (LWIR) HgCdTe high operating temperature (HOT) detector. The detector structure was simulated with commercially available software APSYS by Crosslight Inc. taking into account SRH, Auger and tunnelling currents. A detailed analysis of the detector performance such as dark current, detectivity, time response as a function of device architecture and applied bias is performed, pointing out optimal working conditions.

Infrared detectors are usually characterized by 1/f noise when operating with biasing. This type of noise significantly reduces detection capabilities for low-level and slow signals. There are a few methods to reduce the influence of 1/f noise, like filtering or chopper stabilization with lock-in. Using the first one, a simple 1st-order analog low-pass filter built-in amplifier usually cuts off 1/f noise fluctuations at low frequencies. In comparison, the stabilization technique modulates the signal transposing to a higher frequency with no 1/f noise and then demodulates it back (lock-in amplifiers). However, the flexible tuned device, which can work precisely at low frequencies, is especially desirable in some applications, e.g., optical spectroscopy or interferometry. The paper describes a proof-of-concept of an IR detection module with an adjustable digital filter taking advantage of finite impulse response type. It is based on the high-resolution analog-to-digital converter, field-programmable gate array, and digital-to-analog converter. A microcontroller with an implemented user interface ensures control of such a prepared filtering path. The module is a separate component with the possibility of customization and can be used in experiments or applications in which the reduction of noises and unexpected interferences is needed.

Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards (110). The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

The dual-band avalanche photodiode (APD) detector based on a HgCdTe material system was designed and analysed in detail numerically. A theoretical analysis of the two-colour APD intended for the mid wavelength infrared (MWIR) and long wavelength infrared (LWIR) ranges was conducted. The main purpose of the work was to indicate an approach to select APD structure parameters to achieve the best performance at high operating temperatures (HOT). The numerical simulations were performed by Crosslight numerical APSYS platform which is designed to simulate semiconductor optoelectronic devices. The current-voltage characteristics, current gain, and excess noise analysis at temperature T = 230 K vs. applied voltage for MWIR (U = 15 V) and LWIR (U = –6 V) ranges were performed. The influence of low and high doping in both active layers and barrier on the current gain and excess noise is shown. It was presented that an increase of the APD active layer doping leads to an increase in the photocurrent gain in the LWIR detector and a decrease in the MWIR device. The dark current and photocurrent gains were compared. Photocurrent gain is higher in both spectral ranges.

The paper presents noise measurements in low-resistance photodetectors using a cross-correlation-based transimpedance amplifier. Such measurements usually apply a transimpedance amplifier design to provide a current fluctuation amplification. In the case of low-resistance sources, the measurement system causes additional relevant system noise which can be higher than noise generated in a tested detector. It mainly comes from the equivalent input voltage noise of the transimpedance amplifier. In this work, the unique circuit and a three-step procedure were used to reduce the floor noise, covering the measured infrared detector noise, mainly when operating with no-bias or low-bias voltage. The modified circuit and procedure to measure the noise of unbiased and biased detectors characterized by resistances much lower than 100 Ω were presented. Under low biases, the reference low-resistance resistors tested the measurement system operation and techniques. After the system verification, noise characteristics in low-resistance InAs and InAsSb infrared detectors were also measured.

Photoelectrical characteristics of scanning IR detectors with implemented time delay and integration mode are analyzed. A new “shifted cellular” layout of photosensitive elements in the FPA structure is proposed. Advantages of the new FPA configuration in terms of threshold sensitivity for small-size/point objects are demonstrated. The analysis is based on the Monte Carlo simulation of the diffusion process of photogenerated minority charge carriers in the photosensitive layer photodiode arrays. The analysis is performed taking into account the main photoelectric parameters of FPA elements: photosensitive layer thickness, diffusion length of charge carriers, optical absorption length, their design parameters: geometric sizes of FPA elements, diameters of p-n junctions, and design parameters of the optical system: optical-spot diameter.