An overview of the current understanding of the structural and chemical nature of interfaces involving an alloy layer, as revealed in photoluminescence and excitation spectra, is presented. Systematic studies, including reflection-highenergy- electron-diffraction measurements and computer simulations, reveal in-plane fluctuations in the alloy composition arising from the growth kinetics to be the dominant feature controlling the nature of the confining potentials in high quality samples grown without growth interruption. The role of surface kinetics in relaxing dynamic growth fronts to structurally smoother surfaces upon growth interruption is summarized and its pragmatic consequences for improving interface quality discussed.

Recently we have reported the measurement of RHEED intensity oscillations during Chemical Beam Epitaxy(CBE) of GaAs using triethylgallium(TEG) and As2 derived from an arsine cracker(Appl. Phys. Lett. 50(19), May 11,1987). The existence of RHEED intensity oscillations during CBE growth of GaAs indicates that over the range of conditions studied, growth proceeds via nucleation of islands which grow two-dimensionally as opposed to a vicinal step propagation mechanism. In the same study we observed a significant variation of the GaAs growth rate with substrate temperature at constant flux. In addition, the variation of growth rate with incident flux at constant temperature was found to be non-linear below approximately 500°C and linear above 500'C for incident fluxes yielding maximum growth rates between.2 and 1.8 monolayers/sec. Additional measurements of the dependence of the damping of RHEED intensity oscillations on V/11 ratio have indicated much less sensitivity of the growth front morphology to group V flux in CBE. This behavior is thought to reflect the role of highly mobile, partially saturated ethyl-gallium radicals in epitaxial growth by CBE. Measurements of As2 arrival rate limited intensity oscillations on gallium rich surfaces prepared by pyrolyzing TEG in the absence of As2 have shown that the pyrolysis of TEG is not self-limiting at 500°C and that excess gallium can be deposited on gallium rich surfaces. This paper also describes a simple model of the surface pyrolysis of TEG which is consistent with the above experimental observation.

Islanding and surface diffusion for Ge on Si(111)7×7 and Si(100)2×1 surfaces were examined in a UHV apparatus with in situ scanning Auger/SEM capabilities. At room-temperature uniform growth is observed, while elevated temperatures lead to Stranski-Krastanov growth with complex island size distributions. Extensive surface diffusion is observed on Si(100)2×l; however, surface diffusion is demonstrated to be extremely sensitive to contamination with carbon on the order of ≈0.05 ML, as well as to e-beam irradiation.

We have calculated the stress distribution and critical thickness for the growth of strained epilayers having various values of misfit between the epilayer and the substrate. During formation of epitaxial films, the growth (pseudomorphic) occurs upto a certain thickness with planar spacing normal to the interface being essentially the same both in the substrate and the film. Above a critical thickness it becomes energetically favorable for the film to contain dislocations. This occurs usually by generating glide dislocations near the free surface because there is a lack of dislocation sources in mostly “defect-free” semiconductor materials. We present an analysis of the critical phenomena in semiconductors based upon this experimental fact. In all the previous analyses, the critical step associated with the generation of dislocations was neglected. We also consider finite (island) growth of thin films and its effect on critical phenomena. The experimental results show the presence of glide dislocations in Ge/Si with the extra half planes in silicon substrate.

The growth of copper, silver and gold thin films on tungsten disulfide has been examined as a model of metal contacts on a layered semiconductor. All three metals were found to grow epitaxially on the WS2. However, Cu appears to form a discontinuous film while Au and Ag grow layer by layer. Such epitaxial growth is somewhat surprising since there is a large lattice mismatch between the metals and the WS2.

High resolution electron microscopy has been used to determine the atomic structure at the epitaxial CaF2 /Si(111) interface before and after a rapid thermal anneal. Direct Ca-Si bonding at the interface, with 8-fold coordinated Ca atoms is observed in as-grown layers. Fluorine is preferentially removed from the interface during a rapid thermal anneal leaving 5-fold coordinated Ca atoms. A dramatic improvement in the electrical properties of the interface is observed after annealing. The measured interface state density is reduced from ≳1013 cm−2 to ≲1011cm−2. This has been correlated with the removal of F from the interface. No evidence for direct F-Si bonding is observed.

We present in this paper the effect of heat treatments applied to a 400 nm GaAs layer grown by MBE on a (001) Silicon substrate. These heat treatments have been applied during or after the growth of the GaAs, in order to improve the crystalline quality of the layer. RBS and TEM observations have been performed to study the improvement of the crystalline quality of the GaAs layer. Specimens, prepared by cross-section technique along both (110) and (170) planes and plane view, have been studied by TEM. Observations of cross-section by HREM show an interface roughness of about 1.5 nm before and after heat treatments. A roughness, observed also by RHEED, appears in the first stage of growth. Although the density of threading dislocations decreases after heat treatments.

Transition layers in GaAs/AlAs superlattices were studied by high resolution transmission electron microscopy (HRTEM) observations and Raman scattering measurements. We clarified that arrays of bright spots at the interface in the TEM image is a good indicator of the interfacial configuration and that a high atomic step density with intervals of less than 10 nm is necessary for Raman characterization using confined LO phonons.

We characterized the growth temperature dependence of the transition layers at the GaAs/AlAs interfaces. For a sample grown at 500'C, the extent of the transition layers is about one monolayer and that of the interfacial step intervals is more than 10 nm. For a sample grown at 700 0 C, these values are about two monolayers and less than 3 nm, respectively.

This paper reviews the requirements for mercury cadmium telluride material which is suitable for far infrared detectors. This is followed by substrate and reactor considerations, leading to its direct alloy growth by organometallic vapor phase epitaxy.

It is shown that HgCdTe can now be grown with electrical properties and areal compositional uniformity that are suitable for focal plane arrays, operating in the 10.6 Am range.

Two low temperature metalorganic chemical vapor deposition growth techniques, the pre-cracking method and the plasma enhanced method, will be discussed. The pre-cracking technique enables one to grow high quality epitaxial Hg1−xCdxTe on CdTe or CdZnTe substrates at temperatures around 200–250°C. HgTe-CdTe superlattices with sharp interfaces have also been fabricated. Furthermore, for the first time, we have demonstrated that ternary Hg1−xCdTe compounds and HgTe-CdTe superlattices can be successfully grown by the plasma enhanced process at temperatures as low as 135 to 150°C. Material properties such as surface morphology, infrared transmission, Hall mobility, and interface sharpness will be presented.

Films of HgCdTe with x < 0.6 and of HgZnTe with x < 0.26 have been grown by molecular beam epitaxy (MBE). Very high electron mobilities have been achieved for both materials in the small bandgap region. Hall mobilities at 77K reach 4.8 × 105 cm2 /V-s for Hg0 87 Zn0.13 Te, and 3.1 × 105 cm2/V-s for Hg0.87 Zn0.13 Te. HgCdTe growth was easily extended to the 1.5 – 3 μm wave length range. Attempts to extend HgZnTe to these bandgaps were unsuccessful due to defects that are induced by surface roughness in high Zn-content films. These results suggest that HgCdTe is the more suitable material for MBE growth for near infrared applications.

Influential factors to the detectivity of n-CMT grown by liquid phase epitaxy on CdTe(111)B substrate are investigated. The factors are such as qualities of the substratesdopants and electrical parameters by which photoconductivity in CMT is governed.

We show that the doping with small amounts of In is an appropriate mean not only to raise the mobility but also to make reproductivity better. The In- doped epitagia�r after annealed has the highest mobility among tested in 3×10 cm5 /Vsec, and the photoconductive lifetime in 0.54 μsec at 77K.The resultant detectivity of an infrared device is 3×1010 cmHz1/2 w−1.

Photoassisted molecular beam epitaxy (PAMBE), in which the substrate is illuminated during film growth, is being employed in a new approach to controlled substitutional doping of II–VI compound semiconductors. Substitutional doping of these materials has been a long standing problem which has severely limited their applications potential. The PAMBE technique gives rise to dramatic changes in the electrical properties of as-grown epilayers. In particular, highly conducting n-type and p-type CdTe films have been grown using indium and antimony as n-type and p-type dopants, respectively. Double-crystal x-ray rocking curve data indicate that the doped epilayers are of high structural quality. Successful n-type doping of CdMnTe, a dilute magnetic semiconductor, with indium has also been achieved. Most recently, the photoassisted growth technique has been employed to prepare doped CdMnTe-CdTe quantum well structures and superlattices. In addition, HgCdTe films which exhibit excellent optical and electrical properties as well as exceptional structural perfection have been grown by the PAMBE technique.

Layered samples of cadmium telluride grown epitaxially on gallium arsenide substrates have been investigated by means of scanning tunneling microscopy (STM). The surface geometric and electronic structures are both of interest. Techniques were developed to remove the native oxide by etching, or to create a fresh surface by cleaving, and to protect them from oxidation by employing mineral or paraffin oil media. STM studies were conducted within the protective medium. These techniques were adapted and tested for both etched and cleaved samples of Si, CdTe and HgTe. The currentvoltage characteristics of the CdTe surface were investigated during dynamic changes of the tunnel current and barrier height while the probe-to-sample separation (gap) was static. Recorded values are shown for current versus bias for several constant gap values. A range of bias values has been employed to test a possible solution for the problem of interference between the contributions from geometric and electronic structure factors.

The integration of several optoelectronic device functions onto a common substrate material is an area which is currently being actively pursued. In an effort to achieve this objective, experiments are under way to examine the epitaxial growth and material properties of a variety of both II–VI and III–V compounds grown on a substrate where the II–VI/III–V heterostructure can be utilized. This paper describes some recent developments involving the molecular beam epitaxial (MBE) growth and characterization of two important II–VI/III–V heterostructures: ZnSe/GaAs and InSb/CdTe;. a comparison is made between epitaxial layer/substrate interfaces and epilayer/epilayer interfaces for both heterostructures. The ZnSe/GaAs heterointerface, having a 0.25% lattice constant mismatch, has potential for use in passivation of GaAs devices. The InSb/CdTe heterointerface possesses an even closer lattice match, ∼0.05% (comparable to the (Al,Ga)As/GaAs material system), and is motivated by possible device applications provided by InSb/CdTe quantum wells.

We have grown ZnSe epitaxial layers on bulk GaAs substrates and on GaAs epitaxial layers, with both As-rich and Ga-rich surface terminations. We have also grown ZnSe on AlAs epitaxial surfaces with different As to Al ratios. In all cases, abrupt, layer-by-layer growth is observed on the As-rich surfaces, while 3-dimensional nucleation is observed on the group III-rich surfaces. GaAs was also grown on ZnSe layers. In this case, microtwins form at the interface whose density diminishes as the layer is made thicker. A growth model is proposed consistent with these results which requires over-all electronic balance at the interface.

Optical and transmission electron microscopy have been used to study cracks appearing in ZnSe/ZnSxSe1−x (x ∼ 0.38) superlattices grown by Molecular Beam Epitaxy. It Is shown that when a fracture occurs it is confined, in most cases, to the superlattice and propagates along <011> cleavage directions in these <001> oriented epilayers. Cracks were not observed in all superlattices and their onset is discussed in relation to sulfur concentration, overall superlattice height, individual superlattice layer thicknesses, and stress, tensile or compressive, due to lattice mismatch and thermal expansion differences between buffer layer and superlattice. It was found that by adjusting the controllable parameters, cracks in the superlattices could be eliminated. Orientation and density of these features have been related to asynnmetric cracking associated with the zincblende structure of these II-VI materials. Experimental results are shown to be in agreement with theoretical predictions of critical heights for the onset of cracking.

ZnSe-ZnS multilayers have been prepared by atmospheric. pressure metal organic chemical vapour deposition (M0CVD) using dimethylzinc, hydrogen sulphide and hydrogen selenide. Layer thicknesses down to 500Å have been obtained and the interfaces, as measured by secondary ion mass spectroscopy (SIMS) and electron microscopy, are regular. A notable improvement in interface abruptness was observed with better control of experimental procedures and more especially with the growth of a ZnSe buffer layer between the GaAs(100) substrate and multilayers.

Back-doping experiments with intentional donors (Al, Cl, Ga and In) and acceptor (Na) species have been conducted in the recrystallization travelling-heater-method (THM)-grown ZnSe single crystals. Sharp bound-exciton lines and associated two-electron or two-hole transitions appear clearly and their bind-ing energies can be accurately estimated using central cell corrections. Uni-axial stress measurements on the l1d line at 2.783 eV and on the l2In line at 2.7968eV confirm that the spatial symmetry of the localized centers which bind excitons is Td. Utilizing the present THM ZnSe crystal as a substrate for ZnSe layer with good optical-quality was homoepitxially grown by metalorganic-chemical- vapor-deposition and exhibited a strong donor-bound exciton line locating at 2.7964 eV, probably Al. Low-resistive n-type layer with 0.1ω·cm was achieved by doping with Al from trimethylaluminum source.

ZnO layers have been heteroepitaxially deposited on sapphire using organometallic chemical vapor deposition at atmospheric pressure. The quality of the layers was assessed using photoluminescence spectroscopy at 16K. The layers exhibited strong ultraviolet near bandedge luminescence. The dependence of near bandedge and deep level photoluminescence emission on deposition conditions was examined.