The surface morphology and crystallinity of HgCdTe films grown by molecular beam epitaxy (MBE) on both CdZnTe and CdTe/Si (211)B substrates were characterized using atomic force microscopy (AFM), as well as scanning (SEM) and transmission (TEM) electron microscopy. Crosshatch patterns and sandybeach-like morphologies were commonly found on MBE (211) HgCdTe epilayers grown on both CdZnTe and CdTe/Si substrates. The patterns were oriented along the 213 Â Ã , 231 Â Ã , and 011 Â Ã directions, which were associated with the intersection between the (211) growth plane and each of the eight equivalent HgCdTe slip planes. This was caused by strain-driven operation of slip in these systems with relative large Schmid factor, and was accompanied by dislocation formation as well as surface strain relief. Surface crater defects were associated with relatively high growth temperature and/or low Hg flux, whereas microtwins were associated with relatively low growth temperature and/or high Hg flux. AFM and electron microscopy were used to reveal the formation mechanisms of these defects. HgCdTe/HgCdTe superlattices with layer composition differences of less than 2% were grown by MBE on CdZnTe substrates in order to clarify the formation mechanisms of void defects. The micrographs directly revealed the spiral nature of growth, hence demonstrating that the formation of void defects could be associated with the Burton, Cabrera, and Frank (BCF) growth mode. Void defects, including microvoids and craters, were caused by screw defect clusters, which could be triggered by Te precipitates, impurities, dust, other contamination or flakes. Needle defects originated from screw defect clusters linearly aligned along the 011 Â Ã directions with opposite Burgers vector directions. They were visible in HgCdTe epilayers grown on interfacial superlattices. Hillocks were generated owing to twin growth of void or needle defects on (111) planes due to low growth temperature and the corresponding insufficient Hg movement on the growth surface. Therefore, in addition to nucleation and growth of HgCdTe in the normal two-dimensional layer growth mode, the BCF growth mode played an important role and should be taken into account during investigation of HgCdTe MBE growth mechanisms.

Thin films of zinc sulfide (ZnS) with different concentrations of zinc acetate have been made by chemical bath deposition technique in acidic medium (pH = 5) on glass substrate using zinc acetate and sodium sulfide as sources of Zn+2 ion and S−2 ion, respectively, and ethylenediaminetetraacetate as complexing agents and sulfuric acid to adjust pH value at a constant deposition temperature of 85°C, and the deposition time of 90 minutes was used. The effect of the concentration of metallic precursor on the structural, morphological, and optical properties of chemical bath deposited zinc sulfide thin films was investigated in this study. The XRD result confirmed mixed phases of crystalline and amorphous structure dominating other phases, which is witnessed by larger crystallite size than other phases. It reveals that the thin films had hexagonal structure at the medium concentration with preferred orientation along (111) plane, and at lower and higher concentration, it showed that film has an amorphous structure in nature. The crystallinity of all the phases significantly enlarged with increasing the zinc precursor concentration. The SEM micrographs showed high-pitched edged irregular-shaped grains covering the substrate with pinholes and bangs. The optical properties investigated by the UV-VIS spectrometer specified a decrease in the optical bandgap of the films between 3.5 eV and 2.6 eV as the zinc acetate concentration in the solution increased from 0.1 to 0.2 M. It showed that the zinc sulfide had high absorption in the UV radiation. The main finding of this paper is that metallic precursor concentration has a significant role in the optical, morphological, and microstructural properties of the cobalt sulfide thin films, which are most suitable for photovoltaic applications.

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