Jakub Wenus

Two-dimensional analysis of double-layer heterojunction HgCdTe photodiodes

In this paper, the performance of P-on-n double-layer heterojunction (DLHJ) HgCdTe photodiodes at temperature 77 K is analyzed theoretically. Calculation has been performed for the backside-illuminated configuration. The effect of photodiode base layer geometry on quantum efficiency and R/sub o/A product is analyzed. Also, the effect of lateral collection of diffusion current and photocurrent on photodiode parameters has been shown. Moreover the dependence of the p-n junction position within heterostructure on the band-gap energy profiles and photodiode performance is presented. Finally, the influence of the composition gradient and p-side doping concentration on photodiode parameters is described briefly.

Surface leakage current in HgCdTe photodiodes

This study describes fabrication of heterojunction HgCdTe photodiodes passivated with a wide band-gap CdTe epitaxial layer. The current-voltage characteristics of these photodiodes with and without passivation have been investigated. It is shown that for reverse bias the measured I-V characteristics can be explained by a surface tunneling current and surface generation current. The breakdown voltage is observed to decrease monotonically with increasing temperature, a trend that is directly opposite to what would be expected from a pure tunneling mechanism. Additional information on surface limitations is obtained from analyzing the R0A product as a function of temperature. The performance of both type of p-n VLWIR HgCdTe photodiodes (with and without the passivating layer) have been compared.

Analysis of VLWIR HgCdTe photodiode performance

The performance of very long wavelength infrared (VLWIR) HgCdTe photodiodes at temperatures ranging from 77 K up to 150 K is presented. The effect of inherent and excess current mechanisms on quantum efficiency and dynamic resistance-area RA product is analysed. Different methods of determining the ideality factor are shown and among them the one based on the use of RA product versus bias voltage proves to be the most reliable. At higher temperatures, however, the calculated ideality factor does not give any useful information about the nature of the p-n junction current due to significant influence of the series and shunt resistances. A comparison of the experimental data with the results of analytical and numerical calculations shows that the photodiodes with cut-off wavelength up to 14.5 μm are diffusion-limited at temperatures exceeding 100 K.

LPE growth of Hg1-xCdxTe heterostructures using a novel tipping boat

A novel tipping boat for liquid phase epitaxial growth of mercury cadmium telluride from Te-rich solutions has been proposed. By optimizing the growth parameters and the construction of graphite boat it was possible to obtain in situ Hg1-xCdxTe heterostructures. The successful fabrication of long wavelength Hg1-yCdyTe/Hg1-xCdxTe heterostructures on semi-insulating CdZnTe substrates is presented. The heterostructures consist of a thin 1-2 micrometers layer on n-type 10-15 micrometers thick HgCdTe epilayer. The characterization of double-layer heterostructures was carried out using different methods. Variations in the layer thickness were determined by microscopic examination of cleaved samples. Average composition was determined from an IR absorption measurement on the central area of the layers. Chemical analysis and the Cd, Hg and Te profile compositions at different depths of the epitaxial layers were performed using secondary ion mass spectrometry. Transport properties were measured in temperature range of 77-300 K using the Van der Pauw arrangement. The paper also reports an experimental innovation of the in situ preparation of the mercury cadmium telluride heterostructures using the tipping method from Te- rich solutions performed in a one-zone reactor.

Gate-controlled narrow-bandgap photodiodes passivated with rf sputtered dielectrics

Gate-controlled diodes were made by using evaporated indium electrodes overlapping the edge of mesa diodes, isolated from the surface by a layer of ZnS or by native anodic oxide of InSb or HgCdTe. The resulting 3D device characteristics with gate voltage as a parameter have been investigated. Relative spectral responses and I-V characteristics were measured at 77 K. The R0A product is used as an indicator of the dark current of photodiodes passivated with ZnS layer. A plot of R0A values versus gate potential shows that the optimum R0A values are obtained at small positive gate bias voltage. This dependence is consistent with surface recombination influencing the R0A product. The results of a 2D model for calculating gate-induce surface leakage currents due to band-to-band tunneling are presented. The exact quantitative comparison cannot be made between our results and theory, since the active tunneling area is not known.

Impact of the LWIR photodiodes geometry on their basic parameters

This paper concerns HgCdTe heterostructure photodiodes for detection of infrared radiation from 8-12micrometers spectral range. Heterostructures were made by liquid phase epitaxy on the CdZnTe substrates. The cap layer of wider energy gap was used to suppress the generation-recombination current from the top contact. P-on-n junctions were placed in the narrow band-gap area close to the graded region. It was accomplished by appropriate selection of the cap layer thickness and adequate choice of parameters of the As diffusion process. Photodiodes were mesa delineated and illuminated through the substrate. Analysis of the impact of p-n junction location within a heterostructure, contact locations and mesa depth on photo diode parameters, was carried out. The experimental results were compared with two-dimensional numerical calculations performed in APSYS.

LPE growth of Hg1-xCdxTe heterostructures from Te-rich solutions

The successful fabrication of long wavelength Hg1-yCdyTe/Hg1-xCdxTe heterostructures (Y

Status of HgCdTe photodiodes at the Military University of Technology

GTRx) on semi- insulating (111)CdZnTe substrates is presented. The heterostructures consist of a thin 2-5 micrometers layer on n-type 10- 15 micrometers thick HgCdTe epilayer. A novel tipping boat for liquid phase epitaxial growth of mercury cadmium telluride from Te-rich solutions has been proposed. The characterization of double- layer heterostructures was carried out using different methods: microscopic examinations, infrared microscopic transmission, and scanning electron microscopic measurements. Electrical properties were measured in temperature range of 77-300 K using the Van der Pauw arrangement. By optimizing the growth parameters and the construction of graphite boat it was possible to obtain high quality, relatively abrupt Hg1-xCdxTe heterostructures.