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.
ZnTe was grown on GaAs(211)B by molecular beam epitaxy (MBE). Structural properties and strain relaxation at the ZnTe/GaAs(211)B interface were investigated by high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM). Application of digital image processing involving a filtered inverse fast Fourier transformation revealed an array of misfit dislocations at the interface and allowed strain relaxation to be estimated. Only one twin defect was observed in the HRTEM images, and details of this twin defect were investigated by STEM.
CdZnTe-based heterojunction p-i-n or M-p-n detectors using HgTe/HgCdTe superlattice contacts are modeled and designed to reduce leakage currents under high electric fields and thereby improve x-ray and c-ray detector performance. The employment of an n-type HgTe/HgCdTe superlattice as a contact layer can theoretically result in significantly less leakage current compared with a contact layer using either bulk semiconductor or metal contacts. The benefits arise from the ability to design HgTe/HgCdTe superlattices to have large carrier effective masses in the electric field direction, which results in low carrier velocities. Nevertheless the density of states is lower than that of a comparable bulk semiconductor, which results in low carrier concentrations.
The authors report the results of successful growth of single crystalline PbSe on Si (211) substrates with ZnTe as a buffer layer by molecular beam epitaxy. Single crystalline PbSe with (511) orientation was achieved on ZnTe/Si (211), as evidenced by RHEED patterns indicative of 2 dimensional (2D) growth, x ray diffraction rocking curves with a full width at half maximum as low as 153 arc sec and mobility as large as 1.1×104cm2V-1s-1 at 77 K. Cross hatch patterns were found on the PbSe(511) surface in Nomarski filtered microscope images suggesting the presence of a surface thermal strain relaxation mechanism, which was confirmed by Fourier transformed high resolution transmission electron microscope images.
The interface of ZnTe/Si(211) grown by molecular beam epitaxy was investigated by high-resolution transmission electron microscopy. Several types of defects such as misfit dislocations, stacking faults, agglomerations of vacancies, and precipitates were observed and studied by electron microscopy at the ZnTe/Si interface. The distribution of misfit dislocations at the interface was revealed with the assistance of the fast Fourier transformation filtering technique. A stick-and-ball interface model including misfit dislocation geometry is proposed. The possible origins of the stacking faults, vacancies, and precipitates are discussed.
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