Annealing And Device Characterization Of Hgcdte Grown On Cdte/Si Substrates.

摘要

Infrared sensors have long been utilized for personal, commercial, and government applications. Mercury cadmium telluride (MCT) is the highest quality material for infrared detection. Its limitation comes in the substrate that it is grown on. Cadmium zinc telluride (CZT) is the substrate of choice for its ability to be lattice matched to the MCT epilayer grown on it, but its limited size of less than 7x7 cm2 and high cost of ;Thermal cycle annealing (TCA) is the heating and cooling of a sample over a specified period of time. TCA has been applied to MCT in the past, but has had limited application due to interdiffusion of the as-grown layer structures. This was due to the high annealing temperature of 500°C and four cycles of 5 minutes at the high temperature. A new annealing setup has been made that allows dislocation reduction at high annealing temperatures as low as 350°C and 128 cycles of less than 5 seconds each at the high temperature. This results in a dislocation density reduction to 1x10 6 cm-2 with minimal diffusion for MCT grown on silicon-based substrates. Conducting 512 cycles at a high annealing temperature of 400°C did not result in further dislocation density reduction. This pushed the focus of the work onto other methods of dislocation reduction.;To reduce the dislocation density further, etched mesa bar structures have been utilized to enhance dislocation reduction during thermal annealing. The dislocation density of mesa structures was studied for their dependence on anneal time, temperature, and etch depth. It was found that a single, 5-minute thermal anneal at 400°C can induce dislocation reduction with a dependence on mesa bar angle relative to the [01¯1] orientation. It is also found that dislocation density reduction is proportional to etched mesa bar width. A minimum dislocation density of 1x105 cm-2 is observed with a 10 mum wide mesa bar, which is on par with the dislocation density of MCT grown on CZT. With this result, the etched mesa bar structure is applied to device layers and devices are fabricated and tested. The dark current density of devices on mesa bars is lower than that of planar devices. Therefore, the application of these results to large arrays can bridge the gap in device performance between MCT grown on CZT and MCT grown on CdTe/Si.