MBE Growth of Strained-Layer InSb/InAlSb Structures
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MBE GROWTH OF STRAINED-LAYER InSb/InAlSb STRUCTURES
C.R. WHITEHOUSE, C.F. McCONVILLE*, G.M. WILLIAMS, A.G. CULLIS, S.J. BARNETT, M.K. SAKER. M.S. SKOLNICK AND A.D. PITT Royal Signals and Radar Establishment, St Andrews Road, Malvern, Worcs WR14 3PS, UK * Now at Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
ABSTRACT The MBE growth and related materials characterisation of InSb/InAlSb strained-layer structures is described. Band-gap considerations and critical thickness calculations are presented and indicate that this material system should offer considerable device potential. Detailed structural studies, performed using both transmission electron microscopy and X-ray diffraction, confirm the growth of high quality multiple quantum-wells, and 2K photoluminescence has shown corresponding energy upshifted transitions. INTRODUCTION InSb-based hetero-junction (HJ) and multiple quantum-well (MOW) structures are attracting increasing interest. The low effective mass of electrons in this material system offers major potential for ultra-high speed transistors, and also quantum-effects on much larger length scales than in the more commonly studied wider band-gap systems [1]. Important possibilities also exist for infra-red detectors and sources [2]. The successful growth of high quality InSb-based MOW structures has thus far, however, been inhibited by the lack of a lattice-matched wider band-gap IllI-V semiconductor partner material required to generate quantum confinement. The authors' previous work has therefore concentrated on the growth of structures based on the closely lattice-matched CdTe/InSb system [3-5]. However, whilst apparent two-dimensional electron gas behaviour has been reported for this material combination [6], our subsequent work has shown that unintentional doping of the InSb well material arises due to tellurium cross-contamination and memory effects [4]. In addition, complex interface chemical reactions are also observed [7]. The present paper provides the first report relating specifically to the MBE growth and associated characterisation of high quality strained-layer InSb/InAlSb structures, although two reports of Raman studies [8] and non-linear optical measurements [9] have already appeared. The variation of energy gap with lattice parameter for the Inl-xAlxSb system is illustrated in Fig 1. This figure indicates that, of all the common binary Il1-V compounds, AlSb possesses the closest lattice match to InSb, and also that the InAlSb alloy range provides the highest rate of change of direct energy gap with increasing lattice mismatch. Therefore, as a first step in the present investigation, calculations were performed, based on the People and Bean energy balance model [10], in order to gain approximate estimates for critical thickness values for single-layer InAISb alloys grown on InSb. The data obtained are summarised in Fig 2 and, whilst remembering the limitations of the model used, indicate that the InAlSb/InSb system should provide viable high-quality MOW structures. F
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