Characterization of mercury cadmium telluride/cadmium zinc telluride epitaxial materials for infrared detectors

HgCdTe (MCT) is one of the most important materials currently in use for infrared photo-detectors. Liquid-phase epitaxy (LPE) is considered to be the most mature method for production of first and second generation MCT-based devices, while molecular beam epitaxy (MBE) is ideally suited for the growth of multilayered heterojunctions. In this dissertation, transmission electron microscopy (TEM) was used for the characterization of MCT epilayers and MCT-based devices grown by LPE and MBE.; The structural damage in MBE-grown MCT multilayer heterojunctions and LPE-grown double-layer heterojunctions, as caused by argon ion milling, was evaluated. In addition to alloy composition and growth conditions, sample cooling during milling and milling parameters (ion-beam energy, current, and milling angle) were confirmed as important parameters that must be controlled. The structural damage showed a very strong dependence on the Cd concentration as well as the conditions used for cooling. These differences were attributed to the greater rate of production of Hg interstitials and faster diffusion which lead to rapid formation of dislocation loops because of greater defect mobility. A possible model for the damage mechanism was proposed.; HgCdTe epilayers grown by MBE on CdZnTe substrates using interfacial layers of HgTe/Care superlattices were investigated. Observations showed that the SL smoothed out the initial substrate surface roughness and also bent or blocked threading dislocations. High quality MBE growth of HgCdTe on CdZnTe substrates using the HgTe/CdTe superlattice interfacial layers was also confirmed.; LPE-grown HgCdTe p-n device structures and the effect of annealing on CdTe passivation layers have been investigated. The CdTe passivation layers were columnar and polycrystalline, and without any obvious epitaxy with respect to the underlying HgCdTe. No obvious microstructural difference was observed due to annealing. However, the interface between CdTe and HgCdTe was rather flat and a high density of twins in the CdTe passivation layers was observed in some regions with a different deposition technique. The use of focused-ion-beam (FIB) milling as an alternative approach for preparing large-area cross-sectional TEM specimens was briefly evaluated. No major structural changes appear to have been caused as a result of the FIB milling process.