Structural and Electronic Properties of GaN/AL Interfaces
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S. PICOZZI*, A. CONTINENZA*, S. MASSIDDA**, A. J. FREEMAN+ INFM - Dip. Fisica - Univ. L'Aquila, 67010 Coppito (L'Aquila), Italy ** INFM - Dip. Scienze Fisiche - Univ. Cagliari, 09124 Cagliari, Italy + Dept. of Physics and Astronomy and Materials Research Center - Northwestern Univ., Evanston, IL 60208 (U.S.A.) *
ABSTRACT The structural and electronic properties of the GaN/Al interface are determined from first principles local density full potential linearized augmented plane wave (FLAPW) calculations. The charge distribution of the gap states as a function of the distance from the interface shows that the gap states induced into the semiconductor by the presence of Al are strongly localized in the junction region. Furthermore, we find that Al does not provide good ohmic contacts on the clean nitrides considered, in contrast with experimental results on chemically treated GaN, but in agreement with recent measurements on the clean surface[l]. We also study some auxiliary systems (all grown on a GaN substrate), i.e. the A1/AIN interface, the GaN/A1N heterojunction and the GaN/Al with an AIN intralayer (GaN-A1N/Al). The transitivity rule for the GaN/Al, AlN/Al and GaN/A1N interfaces is fairly well satisfied and small differences must be ascribed to differences in the interface morphology. Finally, we find that the AIN intralayer does not significantly affect the p-type Schottky barrier height of the GaN/Al interface. INTRODUCTION In the last few years, the nitrides compounds (GaN in particular) have been one of
the most interesting subjects in new materials science, both from the experimental and theoretical point of view [2]. However, the performances of all technological devices based on this compound are strongly dependent on the formation of good metallization contacts, so that the Schottky barrier height (SBH) in these metal/nitrides systems is widely considered of primary importance. Recent experimental works [1, 2, 3] have focused on the deposition of different metals on GaN, but, at least to our knowledge, the GaN/metal junction has not yet been explored theoretically. In this work, we show the results obtained from firstprinciples full-potential linearized augmented plane wave (FLAPW[4J) calculations for the N-terminated cubic-GaN/Al junction, ordered along the (001) growth direction. In order to investigate the structural and electronic properties of the abrupt interface, we also studied an A1/A1N metal/semiconductor interface and a GaN/A1N heterojunction, both grown on a GaN substrate. Starting from recent experimental results [1], showing that repeated cycles of annealing lead to an ordered AIN layer and, possibly, to a dilute GaA1N alloy, we also considered a GaN/Al interface with an AIN intralayer. TECHNICALITIES The supercell approach was used for all the structures considered; in particular, tests performed as a function of the cell dimensions have shown that bulk conditions at both 833
Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
Table I. Structural parameters for the sys
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