Poster abstract

In the past few years, the III-V nitrides have received a great deal of attention. This is due, of course, to the famous blue LED based on GaN. The fundamental problem that was overcome was the efficient p-type doping. Many theoretical and experimental papers have been published in the literature searching for new dopant sources. What hasn't been addressed in great detail is the interaction of hydrogen with these dopants. Hydrogen plays and important role in the nitride family passivating defects such as grain boundaries and vacancies rendering them in most cases neutral and inactive. It is always present in large quantities due to it being part of the growth procedure in normal CVD grown crystals. Passivation of dopants is not new in other materials, such as silicon, but in the nitrides our knowledge is still limited. The most well known case of passivation in the nitride family is the passivation of magnesium by hydrogen in GaN. Although well known there is still no consensus on the microscopic structure of the center. Passivation of magnesium has not been understood if at all studied in the other nitrides. We present ab initio total energy calculations using Density Functional Theory of Mg-N-H and Be-B-H complexes. All calculations use wave functions that are expanded in terms of N gaussian (s, p and d) and they are used in both super-cells and hydrogen terminated clusters of BN. The lowest energy structures are determined by sampling possible configurations and allowing them to relax. The relaxation is done by a conjugate-gradient method, in which the forces are determined using the Hellmann-Feynman theorem and include a Pulay term due to due to the basis set being dependent on the nuclear sites. Various configurations of the hydrogen atom where studied as well as the influence on the complexes gap levels. Local vibrational modes have also been calculated for the lowest energy configurations. [1] C. H. Park and D. J. Chadi, Phys. Rev. B 55, 12995 (1997) [2] I. Gorczyca, A. Svane and N.E. Christensen, MRS Internet J. Nitride Semicond. Res. 3, 48 (1998) [3] I. Gorczyca, A. Svane et al., Phys. Rev. B 60, 8147 (1999) [4] V. B. Torres et al., MRS Internet J. Nitride Semicond. Res. 2, 35 (1997) [5] Okamoto, M. Saito, and A. Oshiyama, Jpn. J. Appl. Phys., Part 2 35, L807 (1996)