Etch pit study of dislocation formation in Hg1−xCdxTe during array hybridization and its effect on device performance

Abstract

The relationship between hybridization force, dislocation (etch pit) density, and device performance has been investigated for devices fabricated from Hg1−xCdxTe liquid phase epitaxy (LPE) material. Coldwelded indium column interconnects are the predominant method used to mechanically and electrically attach mosaic arrays to silicon multiplexers. The mismatch in thermal expansion between the Hg1−xCdxTe photodiode arrays and silicon multiplexers stresses the interconnects when the arrays are cooled to their operating temperature (typically 40–120 K) which can lead to failures. Increased hybridization force improves the mechanical stability of the interconnects but can introduce dislocations in the Hg1−xCdxTe. Dislocations have been reported to degrade the performance of some device structures. The dislocation density in the LPE film after growth was ≊8×105/cm2. We have found no significant change in dislocation density at hybridization forces up to ≊3.9×107 N/m2. At forces on the order of 5.9×107 N/m2 (≊10% of the Vickers hardness), the dislocation density in the films increased to 90×105/cm2 in the areas where the indium columns were. The diffusion limited performance of the test structures at 120 K was not significantly degraded by the increased dislocation density. At 80 K, however, where the devices were modeled to be generation–recombination limited, there was an increase in dark current with increased dislocation density. The structures used in the study were fabricated from LPE Hg1−xCdxTe grown on a CdTe substrate. Implantation of boron into the p-type material through a ZnS passivation layer was used to form junctions. A zero-bias junction resistance of 1000 to 7000 Ω cm2 was typical for the test structures which had a cutoff wavelength of 4.7 μm at 120 K.