Electric fields at the SiC/AlN and SiC/GaN polar interfaces
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Electric fields at the SiC/AlN and SiC/GaN polar interfaces Morad Rouhani Laridjani1, Pierre Masri1, and Jacek A. Majewski2 1 Groupe d’Etude des Semiconducteurs, CNRS-UMR 5650, Université Montpellier 2, cc 074, 12 Place E. Bataillon, 34095 Montpellier CEDEX 5, France 2 Walter Schottky Institute and Physics Department, TU München, Germany
ABSTRACT
We present first-principles calculations of structural and electronic properties of heterovalent SiC/AlN and SiC/GaN heterostructures with wurtzite AlN and GaN films pseudomorphically grown on the 6H-SiC and 3C-SiC substrates along the c-axis. We have investigated reconstructed stoichiometric interfaces consisting of one mixed layer with various lateral arrangements. The preferred bonding configurations of the reconstructed interfaces are found to be Si-N and Ga-C. The calculated valence band discontinuities for SiC/AlN and SiC/GaN heterostructures lie in the range of 1.5 - 2.3 eV and 0.4 - 1.4 eV, respectively. The SiC/AlN heterostructures are predicted to be of type I, whereas SiC/GaN heterostructures can be of type I or II. The polarization induced interface charges are of the order of 4.8 x 1012cm-2 and 0.7 x 1012 cm-2 in SiC/AlN and SiC/GaN junctions, respectively.
INTRODUCTION Thin nitride films are currently attracting much interest because of their potential applications in opto- and microelectronics [1]. An important substrate for epitaxial growth of AlN and GaN is SiC, since it is nearly lattice matched with AlN and has relatively low misfit with GaN. Nitride heterostructures are mainly grown on the 6H-SiC with the growth direction along the hexagonal c-axis. Such heterovalent heterostructures exhibit the built-in macroscopic electric fields [2] that originate from the heterovalent character of the interface and piezo- and pyroelectric character of the constituent bulk materials. In spite of considerable experimental [2,3] and theoretical efforts [4-7], the physical understanding of these intriguing interfaces is still incomplete. In this work, we present first-principles studies of the 6H-SiC/wz-AlN, 3C-SiC(111)/wz-AlN, 6H-SiC/wz-GaN, and 3H-SiC/wz-GaN interfaces. We have calculated formation enthalpies, valence band offsets (VBO's), and polarization induced charges at the interfaces. The theoretical studies of the similar interfaces have been reported previously [7], however, the authors have considered only cubic SiC. Additionally, they used fictitious virtual atoms to simulate the reconstruction of the polar interfaces and have not discussed the interface charges. For 6HSiC/wz-AlN heterostructure, the extensive experimental measurements of the VBO's [3] and electric fields [2] have been reported recently, which allows comparison of theoretical results with experiment. Our calculations are based on the first-principles total-energy pseudopotential method within the local-density-functional formalism [8]. We have used norm-conserving separable pseudopotentials [9] and a preconditioned conjugate gradient algorithm [10] for minimizing the total crystal energy w
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