Energetics and vibrational frequencies of interstitial H-2 molecules in semiconductors

We report a comprehensive investigation of the incorporation of H-2 molecul es in semiconductors. We consider five different materials (Si, GaAs, InAs, GaP and GaN), and use a density-functional-pseudopotential approach. Combi ned with calculations for H-2 in vacuum, these results enable us to examine trends and develop an understanding of the physics of incorporation of a s trongly bound molecule in a semiconducting environment. We find that the vi brational frequency of the interstitial molecules is shifted down significa ntly compared to the free molecule. We also investigate anharmonicity in th e molecular vibrations. The results confirm a recent assignment of Raman li nes to interstitial H-2 in GaAs, but contradict an assignment claiming that the frequency for H-2 in Si is close to the free-molecule value. Finally, we calculate and discuss diffusion of H-2 molecules through a Si crystal. ( C) 1999 Elsevier Science S.A. All rights reserved.