Pseudomorphic ZnTe/AlSb/GaSb Heterostructures by Molecular Beam Epitaxy
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Pseudomorphic ZnTe/AlSb/GaSb Heterostructures by Molecular Beam Epitaxy D.L.Mathine*, J. Han* M.Kobayashi*, R.L.Gunshor*,D.R.Menke*, M. Vaziri*, J.Gonsalves**, N.Otsuka**, Q.Fu***, M.Hagerott***, and A.V.Nurmikko*** *School of Electrical Engineering, Purdue University, West Lafayette, Indiana 47907 "**Materials Engineering, Purdue University, West Lafayette, Indiana 47907 ***Division of Engineering, Brown University Providence, Rhode Island 02912
ABSTRACT A series of pseudomorphic ZnTe/AISb/GaSb epilayer/epilayer heterostructures, aimed at the realization of novel wide bandgap light emitting devices, were grown by molecular beam epitaxy. The low temperature photoluminescence (PL) spectra of ZnTe epilayers showed dominant near-band-edge features related to free, and shallow impurity bound excitons. The PL could be seen at room temperature. Both GaSb and AlSb were doped n-type using a PbSe source.
INTRODUCTION Wide-gap II-VI semiconductors provide an opportunity to realize optoelectronic devices operating in the visible portion of the spectrum. To achieve this objective, experiments are under way to examine the epitaxial growth and materials properties of a variety of layered structures which incorporate both II-VT and III-V compounds that are grown on suitable substrates. One heterojunction that might be suitable for carrier injection and wide-bandgap light emission consists of p-ZnTe/n-AlSb [1,2]; a structure expected to have a favorable band line-up for carrier injection [3]. In this paper we describe epilayer/epilayer ZnTe/AISb/GaSb heterostructures grown by molecular beam epitaxy (MBE) on GaSb substrates. The layer thicknesses were kept pseudomorphic (or nearly pseudomorphic) in order to minimize interfacial dislocations.
Mat. Res. Soc. Symp. Proc. Vol. 161. ©1990 Materials Research Society
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DISCUSSION OF EXPERIMENTS To avoid unintentional doping during the growth of the II-VI/III-V structures, two isolated MBE growth chambers, connected by an ultra high vacuum (UHV) transfer tube, were used. The active interface was preserved by transferring the sample between growth chambers in the UHV transfer module. All of the epilayers for this study were grown on GaSb (001) substrates. The substrates were given an initial degrease followed by etching in HCI [4]. ZnTe was grown at a substrate temperature of 320 0 C using elemental sources, and flux ratios were measured by means of a quartz crystal monitor placed at the substrate position. Pseudomorphic ZnTe layers were nucleated on pseudomorphic AlSb layers; the AlSb in turn was grown on homoepitaxial GaSb buffer layers. The substrate temperature was 5500 C, and the Sb 4 to Ga and Sb 4 to Al flux ratios were approximately 2:1 during the growth of both GaSb and AlSb undoped epilayers layers; the growth rates were about 1 A/s. The RHEED patterns of the GaSb and AlSb surfaces during growth showed c(2x6) and (1x3) reconstructions, respectively [5,6].
The evolution of the RHEED diffraction pattern during the nucleation of ZnTe on an MBE-grown GaSb epilayer contrasts t
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