MBE Growth of High Quality (111)B GaAs, GaInAs, AND AlInAs
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MBE GROWTH OF HIGH QUALITY (111)3 GaAs, GaInAs, AND AlInAs P. HARSHMAN, K.J. MALLOY, J. WALKER, J.S. SMITH, AND S. WANG Dept. of Electrical Engineering and Computer Science, University of California, Berkeley, CA 94720
ABSTRACT Growth of (111)B oriented GaAs, GaInAs, and AlInAs by MBE was investigated through a study of surface morphology, R.HEED patterns, and photoluminescence. Considering growth on both nominally oriented and 2 * mis-oriented (111)B GaAs substrates, we have found that MBE growth in the (111)B direction proceeds quite differently than (100) growth. Except in the case of high substrate temperature growth on nominally oriented (111)B substrates, the growth of (111)B GaAs and GaInAs results in films which are characterized by macroscopically rough or faceted surfaces and by weak photoluminescence. We demonstrate that the surface morphology of these macroscopically rough films may be dramatically improved by growing with modulated Ga and In fluxes. Also, we find that AlAs and Al-containing alloys grow much more smoothly than GaAs on the (111)B surface. We report an AlAs/Al.5In.sAs strained MQW structure which exhibits both good surface morphology and good photoluminescence spectra. Growth mechanisms which may explain the observed differences between (111)B and (100) MBE growth are proposed.
INTRODUCTION Recently, there has been considerable interest in (111) oriented zinc-blend semiconductor structures[I],[2],[3]. It was reported that quantum wells grown in the [111] direction possess an enhanced optical transistion, and a low-threshold (111) quantum well laser has been demonstrated[l]. Also, it has been theoretically predicted that coherently strained (111) layers will possess large built-in electric fields through the piezoelectric effect, an effect that vanishes in (100) oriented strained layers due to symmetry constraints[2]. The existence of such strain-induced built-in electric fields can lead to a whole new class of self-biased optical and electronic devices; enhanced nonlinear optical structures[4] and a novel 2-D electron gas structure[5] have already been proposed. Critical to the exploitation of these and other novel (111) structures is an understanding of (111) crystal growth mechanisms, and of the related optimal growth conditions and materials necessary for the attainment of high quality (111) layers. Previous experimental work in the area of (111) epitaxy has concentrated on the growth of GaAs and GaIn.As layers by Molecular Beam Epitaxy (MBE). Vina and Wang found that while MBE growth of GaAs on nominally oriented (111)B GaAs sustrates yeilded poor material, improved quality GaAs could be obtained by growing on 20 misoriented (111)B substrates[61. However, Hayakawa et.al. found that optimal GaAs growth took place on 0.5* mis-oriented (111)B substrates. Most recently, photoluminescence has been reported from both Si doped GaAs and undoped GaAs/GaInAs quantum wells which were grown on nominally oriented (111)B substrates[7],[8]. In the present work, we examine the question of optimal (
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