Dangling-bond defects and hydrogen passivation in germanium

The application of germanium in complementary metal-oxide semiconductor technology is hampered by high interface-state densities. Using first-principles calculations, we investigate the effects of dangling bonds (DBs) and their interaction with hydrogen. We find that Ge DBs give rise to electronic levels below the valence-band maximum. They therefore occur exclusively in the negative charge state, explaining why they cannot be observed with electron spin resonance. The associated fixed charge is likely responsible for threshold-voltage shifts and poor performance of n-channel transistors. We also find that passivation of DBs by hydrogen will be ineffective because interstitial hydrogen is also stable exclusively in the negative charge state. (C) 2007 American Institute of Physics.