Analysis of Crosstalk in HgCdTe based Vertical Photoconductive LWIR Detector Arrays

HgCdTe is a well known material for Infrared detection applications because of its special properties like high absorption coefficient, adjustable bandgap and moderate dielectric constant etc. Vertical PC detectors of HgCdTe are very easy to fabricate as compared to the other detectors with the desired uniformity and therefore, these detectors may be proved better choice if the cost and the yield are considered. The proposed vertical PC detector design improves the fill factor of the detector array and allows the access of individual elements without the need of integrated circuit for their readout. The structure virtually does not have any optical crosstalk due to diffusion current, but suffers from the electrical crosstalk because of the networking of its element. This paper presents an analysis of the crosstalk for the focal plane array (FPA) of vertical PC detectors. We demonstrate that the networking reduces the detectivity by a factor strongly dependent on the number of rows and columns in the FPA

Effect of Loading Rate on Creep Properties of HgCdTe Epitaxial Films

Nanoindentation creep studies were performed on Hg1-xCdxTe (x~0.29) epitaxial films using different loading rates of 0.5 mN.s-1, 1 mN.s-1, 2 mN.s-1 and 4 mN.s-1, keeping a constant peak load of 10 mN. A constant hold time of 20 sec at peak load was maintained for all experiments. The effect of loading rate on creep behaviour of material has been investigated. Creep displacement had shown increasing trend with increase of loading rates. Stress exponents were extracted using creep curve fitting with an empirical equation. A strong dependence of loading rate on stress exponent was observed. The value of stress exponent was found varying in the range 0.60-1.76, 0.96-2.23, 0.98-2,87 and 0.90-2.81 for loading rates 0.5 mN.s-1, 1 mN.s-1, 2 mN.s-1 and 4 mN.s-1, respectively. The change of stress exponent was attributed to change of creep mechanism. Hardness and elastic modulus were extracted from load-displacement curves and it was found that with the increase of the loading rate hardness increases, while elastic modulus remains constant. A correlation between variation of hardness and creep displacement has also been presented

Cathodoluminescence Studies of Nanoindented CdZnTe Single Crystal Substrates for Analysis of Residual Stresses and Deformation Behaviour

Nanoindentation-induced residual stresses were analysed on (111) Te face CdZnTe single-crystal substrates in this study. CdZnTe substrates were subjected to nanoindentation using cube corner indenter geometry with a peak load of 10 mN. Loading rates of 1 mN/s and 5 mN/s were used in the experiments, with a holding time of 10 s at peak load. Residual stresses on the indented region were analysed from load-displacement curves and explained using dislocation generation and elastic recovery mechanisms. Residual stresses were found to be of compressive type, just on the indented surface. The slip lines along the slip directions of this material were clearly visible in the FE-SEM images of the indents. Indents and surrounding surfaces were characterized using the Cathodoluminescence (CL) technique. CL mapping of the indented surface revealed the dislocation generation and their propagation behaviour just beneath the indenter as well as in the surrounding surfaces. The dislocations act as non-radiative recombination centres and quench the CL intensity locally. Dark lines were explained as the presence of dislocations in the material. CL mapping analysis shows that both the rosette glide and tetrahedral glide of dislocations are the primary deformation mechanisms present in CdZnTe. A rosette structure was observed in the CL mapping. CL spectra at 300 K of un-deformed CdZnTe show a peak at 810 nm wavelength, which corresponds to near-band-edge emission. After indentation, the CL spectra show the peak intensity at 814 nm and 823 nm wavelengths at the edge of the indents created with a loading rate of 1 mN/s and 5 mN/s, respectively. These peak shifts from 810 nm were attributed to the tensile residual stresses present in the indented material