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Surface crater defects in HgCdTe epilayers grown by molecular-beam epitaxy have been investigated using cross-sectional scanning and transmission electron microscopy, as well as atomic force microscopy. These defects originated primarily within the HgCdTe films, and were shown to be associated with the local development of polycrystalline morphology. High-resolution observations established the occurrence of finely spaced HgCdTe/Te intergrowths with either semicoherent or incoherent grain boundaries, as well as small HgCdTe inclusions embedded within Te grains.

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Crater defects on the surfaces of HgCdTe epilayers grown by molecular beam epitaxy have been investigated. A semiempirical model coupled with observations by transmission electron microscopy was used to analyze the defect formation mechanism. We find that Te2 dissociation plays an important role. The defect density can be controlled by adjusting growth conditions such as the substrate growth temperature, Hg flux, growth rate and composition. Tight control over the pretreatment procedures before molecular beam epitaxy growth is also necessary.

Transmission electron microscopy (TEM) is widely used for the characterization of the microstructure of Hg1−xCdxTe epilayers. Traditional TEM sample preparation methods, which usually involve argon ion milling, can easily cause damage to the material, and the size and density of the induced defects depend on the milling conditions. In this work, the structural damage caused by argon ion milling of Hg1−xCdxTe epilayers has been investigated. Multilayer samples with different Hg concentrations, as grown by molecular beam epitaxy, and p-n heterojunctions, as grown by liquid-phase epitaxy, have been examined. It is shown that, in addition to the milling conditions, the extent of the ion-induced damage depends sensitively on the Hg concentration of the Hg1−xCdxTe alloy as well as the epilayer growth conditions (i.e., Hg rich or Te rich). A possible mechanism that explains these results is briefly discussed.

Interfacial layers including HgTe∕CdTe superlattices (SLs) were introduced during the molecular-beam epitaxy growth of HgCdTe on CdZnTe (211)B substrates. Transmission-electron-microscopic observations show that the SLs smooth out the substrates’ surface roughness during growth, and can also bend or block threading dislocations in a way that prevents their propagation from the substrate into the functional HgCdTe epilayers. An average etch pit density value in the low-105cm−2 range was reproducibly achieved in long wavelength HgCdTe samples, with the best value being 4×104cm−2. Photoconductive decay lifetime measurements give values approaching theoretical limits, as determined by the intrinsic radiative and Auger recombination mechanisms. The use of such interfacial layers thus leads to enhanced growth yields and material properties.

HgTe/Hg 0.05 Cd 0.95 Te superlattices (SLs) were grown on (112)B oriented Cd 0.96 Zn 0.04 Te substrates using molecular beam epitaxy (MBE). The SLs, consisting of 100 periods of 80-Å-thick HgTe wells alternating with 77-Å-thick Hg 0.05 Cd 0.95 Te barriers, were designed to operate as detectors in the far-infrared (FIR) region. Infrared absorption spectroscopy, high-resolution transmission electron microscopy (TEM), Hall effect measurements, and x-ray diffraction were used to characterize the superlattice layers. A series of annealing experiments were initiated to quantify the temperature-dependent interdiffusion of the HgTe wells and Hg 0.05 Cd 0.95 Te barriers and consequently their degradation, which shifts the absorption edges of the SLs to higher energies, since a hightemperature ex situ anneal is normally required in order to produce the p-type material required for a photovoltaic detector. Results from infrared absorption spectroscopy, TEM, and Hall effect measurements for the annealed samples are presented. A FIR SLs single-element photoconductive (PC) device was designed and fabricated. Both material characterization and device testing have established the applicability of the HgTe/Hg 0.05 Cd 0.95 Te SLs for the FIR region.

Carrier recombination lifetime measurements and analyses based on Shockley-Read-Hall, radiative, and Auger recombination mechanisms were utilized to characterize the material quality of HgCdTe grown by molecular beam epitaxy. The Auger recombination mechanism employed in this analysis is in the theoretical framework according to Beattie and Landsberg ͓Proc. R. Soc. London, Ser. A 249, 16 ͑1959͔͒, which we independently re-evaluated using the electronic band structures computed with a 14-band k · p methodology and direct evaluations of the transition rates. The Levenberg-Marquette method was used to fit the temperature-dependent carrier recombination lifetimes as measured by the photoconductive decay technique. Based on the above methods, carrier recombination lifetime measurements were developed as a routine characterization technique.