Stability of nitrogen in ZnSe and its role in the degradation of ZnSe lasers

We use density functional theory to examine the stability of defects in p-ZnSe that an formed by a transition of the nitrogen acceptor to the interstitial site. We find that the threefold positive complex of the interstitial nitrogen with the remaining vacancy is considerably more stable than the nitrogen acceptor. The formation of the complex is, however, limited by a kinetic barrier of 1.8 eV for the site transition, and the fact that the charge of the defect must change. The energetic position of the defect in the energy gap is about 2 eV above the valence band edge. This is in agreement with optical degradation experiments which show the formation of a deep defect in the p-doped waveguide with a transition energy of about 2.1 eV and the diffusion of a positively charged species. [S0163-1829(99)52548-4].