Dangling bond defects in silicon-passivated strained-Si1−xGex channel layers

Abstract

Dangling bond defects (DBs) in silicon-passivated (1-or 3-nm thick Si cap) strained-(100)Si1-xGex (x=0.25-0.55) layers at interfaces with 1.8-nm thick HfO2 gate dielectric are studied by means of Electron Spin Resonance (ESR) spectroscopy. The results suggest a dominant contribution of Si DBs (Pb0 centers), a considerable fraction of which is located at the interface between the Si substrate crystal and the pseudomorphic Si1-xGex film. The density of Si DBs in the Ge containing samples is significantly lower than at the reference (100)Si/ HfO2 interface and decreases below the ESR detection limit (≈1x10 11 cm-2) with increasing thickness and Ge concentration in the Si1-xGex layer. However, the beneficial effect of Ge becomes less pronounced when the thickness of the Si cap is reduced to 1 nm or in the case of direct deposition of HfO2 on top of uncapped Si1-xGex. From these observations we conclude that DBs are eliminated due to in-diffusion of Ge from the Si1-xGex channel into Si, bringing the concentration of Ge to the range in which generation of Si DBs becomes energetically unfavourable, in agreement with previous observations on condensation-grown Si1-xGex layers.