Showing papers by "Jacek A. Majewski published in 1997"

Exact Kohn-Sham Exchange Potential in Semiconductors

Abstract: A new Kohn-Sham method that treats exchange interactions within density functional theory exactly is applied to Si, diamond, GaN, and InN. The exact local exchange potential leads to significantly increased band gaps that are in good agreement with experimental data. Generalized gradient approximations yield exchange energies that are much closer to the exact values than those predicted by the local density approximation. The exchange contribution to the derivative discontinuity of the exchange-correlation potential is found to be very large (of the order of 5--10 eV).

Stability and band offsets of polar gan/sic(001) and aln/sic(001) interfaces

Abstract: We present first-principles calculations of structural and electronic properties of polar [001]-oriented interfaces between $\ensuremath{\beta}$-SiC substrates and strained cubic GaN or AlN. The formation enthalpies of reconstructed interfaces with one and two mixed layers and lateral $c(2\ifmmode\times\else\texttimes\fi{}2)$, $2\ifmmode\times\else\texttimes\fi{}1$, $1\ifmmode\times\else\texttimes\fi{}2$, and $2\ifmmode\times\else\texttimes\fi{}2$ arrangements are calculated. We find interfaces containing C-N ``donor'' and Si-Ga ``acceptor'' bonds to be energetically highly unfavorable. The most stable interfaces are predicted to possess unsaturated Ga-C and Si-N bonds only. Simple electrostatic arguments suffice to explain the energetically lowest lateral reconstructions among structures that have the same chemical composition. The present self-consistent total-energy minimizations show that atomic relaxations play a crucial role both energetically as well as for the band offsets. Qualitatively, these relaxations can be understood as size effects of the constituent atoms. The electronic valence-band offsets of various stoichiometric interface structures of GaN/SiC(001) and AlN/SiC(001) heterojunctions are found to depend strongly on the chemical composition of the interface layers but are less sensitive to the type of lateral reconstruction. Interfaces that have different chemical compositions but comparable formation enthalpies lead to valence-band offsets in the ranges of 0.8\char21{}1.8 eV and 1.5\char21{}2.4 eV, respectively, depending on the detailed interface mixing. However, the valence-band maximum is found to lie higher in SiC than in GaN or AlN in all cases.

Effects of Substrate Orientation on the Valence Band Splittings and Valence Band Offsets in GaN and AlN Films

Abstract: We present a first-principles study of heteroepitaxial interfaces between GaN and both cubic as well as wurtzite AlN substrates oriented along main cubic or hexagonal directions and of stacking fault interfaces between cubic and wurtzite GaN. Our calculations show that all studied heterostructures are of type I. Valence band offsets for GaN/AlN are nearly independent of the substrate orientation and of the order of 0.8 eV. The valence and conduction band offsets for a stacking fault interface are predicted to be 40 meV and 175 meV, respectively.