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ELECTRON TRANSPORT IN InAs/AISb QUANTUM WELLS: INTERFACE SEQUENCING EFFECTS GARY TUTTLE, HERBERT KROEMER, AND JOHN H. ENGLISH Department of Electrical and Computer Engineering University of California, Santa Barbara, California 93106 ABSTRACT We present data on electron transport in AlSb/InAs/AlSb quantum wells grown by molecular beam epitaxy. Because both anion and cation change across an InAs/Alsb interface, it is possible to grow such wells with two different types of interfaces, one with an InSb-like bond configuration, the other AlAs-like. Electron mobility and concentration were found to depend very strongly on the manner in which the quantum well's interfaces were grown, with high mobilities seen only if the bottom interface is InSb-like. An As-on-Al sites antisite defect model is postulated for bottom AlAs-like interfaces. INTRODUCTION The InAs/AlSb system, first studied by Chang et al.,1 offers the combination of a large 1.3 eV conduction band offset with the high electron mobilities of InAs, 2 a combination that might be used in a variety of device structures. A particularly promising structure is the AlSb/InAs/AlSb quantum well, in which the the very deep well could be used to contain a high-density, high-mobility two-dimensional electron gas. There have already been reports of low-temperature electron mobilities greater than 2x105 cm 2/V.s for InAs/AlSb quantum wells, 23 and similar values for the related InAs/(A1,Ga)Sb and InAs/Ga(As,Sb) quantum wells. However, to the best of our knowledge, there has been no report on one very interesting aspect of this material system: Because both the cation and anion change across an InAs/AlSb (or InAs/GaSb) interface, such quantum wells can have two distinctly different types of interfaces. In one case, the InAs would be terminated with a final layer of In and the adjoining AISb would start with a layer of Sb, leading to InSb bonds across the interface. We call this the "InSb-like" interface:

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Fig. la. InSb-like InAs/AlSb interface Mat. Res. Soc. Symp. Proc. Vol. 145. @1989 Materials Research Society

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In the other case, the InAs would be terminated with a layer of As atoms, which would bond to Al atoms across the interface. This is the "AlAs-like" case:

Fig. 1b. AlAs-like InAs/A1Sb interface

A similar asymmetry exists at the InAs/GaSb interface, and also at the (Ga,In)As/InP interface. Strain induced by asymmetric interfaces in (Ga,In)As/InP quantum wells has been measured using high resolution X-ray diffraction by Vandenberg et al.4 But there do not appear to exist any reports of any asymmetries in the electronic properties. We present here measurements of the electronic properties of A1Sb/InAs/A1Sb quantum wells with different types of interfaces. To study the effects the differing interfaces on electron transport in the quantum wells, we grew and tested four samples: (i) InSb-like interfaces both top and bottom, (U) AlAs-like interface on top and InSb-like on the bottom, (iii) inverse of the second with AlAs-like on bottom and InSb-like on to