Simulated Thermal Effects on Structural and Electronic Properties of GaN
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ELECTRONIC PROPERTIES OF GaN S. SERRA*, L. MIGLIO*, Vincenzo FIORENTINI**, (*) Istituto Nazionale di Fisica della Materia, Dipartimento di Fisica dell'Universita' di Milano, via Celoria 16, 1-20133 Milano (Italy), (**) Istituto Nazionale di Fisica della Materia, Dipartimento di Scienze Fisiche dell' Universita' di Cagliari, via Ospedale 72, 1-09124 Cagliari, (Italy)
ABSTRACT We present preliminary results of tight binding molecular dynamics (TBMD) simulations concerning the thermal effects on the structural and electronic properties of GaN. We derived a semiempirical tight binding (TB) potential which is able to reproduce the band structure and the phase diagram of GaN for zincblende, wurtzite and rock-salt phases. We have found that even at few hundreds K above the experimental melting temperature the local ordering is fairly well conserved, with the fraction of wrong bonds quite low. Defects states appear in the gap at approximately 2.3 eV in agreement to the experimental indication for annealed films.
INTRODUCTION The Nitrides are III-V compounds characterized by high stability and chemical inertness, with large band gaps, from 1.95 eV to 6.4 eV. For these properties they attracted much attention, since the early eighties, for possible applications in high power and high temperature electronic devices. GaN is the most promising among Nitrides [1,2], in particular for future applications in optoelectronics devices, such as light emitting diodes [3] and UV emitting Lasers [4]. Despite the advances in the growth of GaN films, important problems are still open or have not received much attention. Among the former is the nature of native defects and to the second one belongs the thermal effects on GaN. Any application in electronic devices requires a good understanding of the nature of native defects, and the thermal stability of GaN is an essential question for the high temperature applications and for high power electronic devices. In fact, the thermal generation of defects can compromise the properties of these devices. Then a computational investigation on these subjects would be very important, focusing in particular on the characterization of the thermal disorder induced by an high temperature treatment and the related effects on the gap. We used TBMD which optimally coniugates the needs for a good modelling of the interactions with a relatively low computational cost. Large scale simulations and long period of observation which are out of range for fully ab-initio method are instead accessible to TBMD.
THEORY The TB potential has been determined in the framework of the semiempirical two-center approximation [5]. Within this model the potential is constituted by a sum of two terms: the first one, Eb, give the attractive part and is known as the band structure potential; the second one, E., is the repulsive term and phenomenologically accounts for the quantum mechanical repulsion between occupied orbitals.
435 Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
The band structure contribut
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