Study of Interface Properties of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
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Study of Interface Properties of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
Hai Lu, William J. Schaff and Lester F. Eastman Department of Electrical and Computer Engineering, Cornell University Ithaca, New York 14853 Colin Wood Office of Naval Research, 800 N. Quincy, Arlington, Virginia 22217 ABSTRACT In this work, we prepared epitaxial InN on (0001) sapphire with an AlN or GaN buffer layer by molecular beam epitaxy (MBE). A series of samples were grown with different thickness under the optimized growth conditions. Films were characterized by x-ray diffraction (XRD), reflective high-energy electron diffraction (RHEED), atomic-force microscopy (AFM), transmission electron microscopy (TEM) and Hall measurements. By extrapolating the fitted curve of sheet carrier density vs. film thickness to zero film thickness, a strong residual sheet charge was derived, which may be located at the interface between the buffer layer and the InN film, or at the near-surface. It was found that for InN film on AlN buffer, the residual sheet charge is about 4.3×1013 cm-2, while for InN films on GaN buffer, the residual sheet charge is about 2.5×1013 cm-2. At present, we tentatively believe that the residual charge is surface charge accumulation similar to what is observed at the InAs surface. InN samples with Hall mobility beyond 1300 cm2/Vs and carrier concentration below 2×1018 cm-3 were routinely achieved in this study. The first study on InN-based FET structures was performed. Amorphous AlN was used as the barrier material, which was prepared by migration enhanced epitaxy (MEE) at low growth temperature. It was found that the surface morphology is improved after an AlN barrier layer is added to InN. Hg was used as a back-to-back Schottky metallization. Very low leakage current and weak rectifying behavior were observed.
INTRODUCTION Indium nitride, as an important III-V compound semiconductor with many potential applications, has attracted much attention recently. [1] Theoretically this material has higher peak drift velocity and peak overshoot velocity than GaN, large breakdown electrical field and wide bandgap. [2-4] This material is very suitable for FET applications. However, although some important progresses have been made on this material, currently the properties of InN are not ideal for actual device fabrication. There are several basic problems which need attention: First, what is the origin of high background doping of InN? impurities? or specific structural defects? We have been able to grow InN films with Hall mobility more than 1000 cm2/Vs, but the carrier concentration is still very high, which is in the order of 1018 cm-3. Second, what are the interface and surface properties of InN? As will be seen later in this paper, residual sheet charge was observed in InN epitaxial I1.5.1
layers. Third, the lattice mismatch between InN and gate barrier GaN or AlN is very high. Will this be detrimental for InN-based FET applications? In this study, we will first summarize our previous results and indicate
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