Poster abstract

GaN/InGaN/AlGa structures are important as blue light-emitting diodes and lasers. Their success in this role is achieved in spite of low material quality (high density ofthreading defects) compared with that required by, for example, GaAs optoelectronic devices [1]. Dislocations have been associated with the yellow luminescence at 2.2 eV of these materials [2], while other evidence suggests that threading dislocations act as nonradiative recombination centres [3], thereby reducing luminescent efficiency. Theoretical dislocation studies in the last 5 years have focussed on the core geometry and electronic structure of threading dislocations (see review [4]). Glide dislocations have been relatively neglected, in spite of their importance for stress relaxation and experimental evidence for glide driven by stresses generated during cooling after growth [1].

In parallel with studies of glide dislocations in cubic GaN [4] we have undertaken a study of glide dislocations in hex GaN. We choose the simplest such dislocation: the 90 degree glide partial, one of the constituents of dissociated dislocations. Here we report first principles total energies and structures for supercells containing either a dipole of partials, or individual partials within a hydrogenated boundary. We use AIMPRO within local-density functional method, norm-conserving pseudopotentials with non-local core corrections [5]. We apply conjugate gradient optimisation to initial positions from isotropic elasticity theory in a 144 atom supercell L = 32.8 Angstrom, D=15.5 Angstrom, and the thickness of the cell is 3.2 Angstrom. The optimised lattice constants of hex GaN are a=3.162 Angstrom and c=5.143 Angstrom. We investigated the effects of adding different translations to the lattice vectors in the climb direction. These change the global dislocation pattern but do not affect the average dislocation density in the crystal.

[1] D. Cherns, J. Phys. Condensed Matter, 12, 10205 (2000). [2] F. A. Ponce, D. B. Bour, W. Gotz, and P. J. Wright, Appl. Phys. Lett., 68, 57 (1996). [3] S. J. Rosner, E. C. Carr, M. J. Ludowise, G. Girlami, and H. I. Erikson, Appl. Phys. Lett., 70, 420 (1997). [4] A. T. Blumenau, J. Elsner, R. Jones \emph{et al.}, \emph{J. Phys. Condensed Matter , 12, 10223 (2000). [5] R. Jones and P. R. Briddon, Identification of Defects in Semiconductors (Semiconductors and Semimetals vol 51A), ed. M. Stavola (Boston, MA: Academic) chapter 6 (1998).