Thermal cycle annealing and its application to arsenic-ion implanted HgCdTe

Arsenic ion-implantation is a standard device processing step to create selective area p+-HgCdTe (MCT) regions in planar devices. One of the issues associated with the ion-implantation process is the significant structural damage to the MCT epilayer. These structural defects limit the performance of diodes via significant tunneling reverse-bias dark currents. After ion-implantation, a high temperature annealing step is required to activate the implant (arsenic) by moving it into the tellurium sublattice and also to heal the lattice damage caused by the implantation process. In this study, we have used thermal cycle annealing (TCA) to decrease ion implantation damage. In TCA, we rapidly heat and cool an MCT sample, which provides an additional degree of freedom that is not obtainable with conventional annealing. We have successfully performed TCA for dislocation defect reduction in in-situ indium-doped MCT with limited inter-diffusion between the absorber layer and cadmium rich cap layer. We also investigated the application of TCA to arsenic ion-implanted MCT. Defects were studied using scanning electron microscopy (SEM) after subjecting the samples to Benson etching to decorate the defects. Mercury-deficient and tellurium-saturated overpressure anneals were performed in an attempt to increase mercury vacancy concentrations and, thereby, increase dislocation climb. Such anneals significantly increased the etch pit density (EPD) in both ion-implanted and un-implanted MCT. By cycle annealing, we have also shown EPD reduction in arsenic ion-implanted, long bar shaped MCT mesas formed on CdTe/Si substrates.