MECHANISM FOR HYDROGEN DIFFUSION IN AMORPHOUS-SILICON

Tight-binding molecular-dynamics calculations reveal a mechanism for h ydro en diffusion in hydrogenated amorphous silicon. Hydrogen diffuses through the network by successively bonding with nearby silicons and breaking their Si-Si bonds. The diffusing hydrogen carries with it a n ewly created dangling bond. These intermediate transporting states are densely populated in the network, have lower energies than H at the c enter of stretched Si-Si bonds, and can play a crucial role in hydroge n diffusion.