XPS Measurement of the SiC/AlN Band-Offset at the (0001) Interface
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INTERFACE Sean W. King,* Mark C. Benjamin,** Robert J. Nemanich*, Robert F. Davis * and Walter R. L. Lambrecht t *Department of Materials Science and Engineering, North Carolina State University, Raleygh, NC 27695 "*Department of Physics, North Carolina State University, Raleigh, NC 27695 tDepartment of Physics, Case Western Reserve University, Cleveland, OH 44106
ABSTRACT X-ray photoelectron spectroscopy is used to determine the band-offset at the SiC/A1N (0001) interface. First, the valence band spectra are determined for bulk materials and analyzed with the help of calculated densities of states. Core levels are then measured across the interface for a thin film of 2H-A1N on 6H-SiC and allow us to extract a band offset of 1.4 ±0.3 eV. The analysis of the discrepancies between measured peak positions and densities of states obtained within the local density approximation provides information on self-energy corrections in good agreement with independent calculations of the latter.
INTRODUCTION Silicon carbide wafers are being used increasingly as substrates for the growth of III-V nitride thin films. In particular, SiC is rater closely lattice matched to AIN (0.9 %) which is often used as a buffer layer for GaN growth. The availability of bulk 6H-SiC substrate wafers of high quality is intrumental for this purpose. Since SiC can also be grown on AIN layers on SiC [1], one may also consider the use of SiC as an active quantum well layer in a AIN/SiC/A1N heterostructure device. From both points of view, the band-offset at the SiC/A1N interface is of obvious interest. To date, only two previous values are available: a theoretical value by Lambrecht and Segall [21 which was for the (110) interface between zincblende SiC and AIN; and an experimental value obtained indirectly from measurements of the Fermi level of 2H-AIN grown on 6H-SiC (0001) by Benjamin et al. [3]. The investigations described here provide a more direct experimental determination of the band offset at-the basal plane interface between 6H-SiC and wurtzite AIN. The procedure consists of measuring the core levels at the interface between a thin film of AIN (0001) grown on a 6H-SiC(0001) substrate and separately determining the energy of the valence band edges with respect to the core levels for thick films. The calculated densities of states are used to aid in the determination of the valence band edge and allow us to obtain some additional information on the electronic structure of the materials. In particular, we obtain results for the difference in quasi-particle self-energy shifts of the N2s and C2s bands with respect to those of the upper N2p and C2p like valence bands.
EXPERIMENT A unique and integrated ultra high vacuum (UHV) system consisting of a 36 ft. long UHV transfer line to which several thin film deposition and surface analysis units are connected was employed in this research. The details of this integrated system have been pre17 8 3 viously described [4]. The as-received, n-type (Nd - 10 -1 /cm ), vicinal 6H-SiC(0001)si 16 17 3 subst
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