Dangling bond defects in silicon-passivated strained-Si_1−xGe_x channel layers

Dangling bond defects (DBs) in silicon-passivated (1- or 3-nm thick Si cap) strained-(100)Si_1−xGe_x (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 (P_b0 centers), a considerable fraction of which is located at the interface between the Si substrate crystal and the pseudomorphic Si_1−xGe_x 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 (≈ 0.8 × 10¹¹cm⁻²) with increasing thickness and Ge concentration in the Si_1−xGe_x 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 Si_1−xGe_x. From these observations we conclude that DBs are eliminated due to in-diffusion of Ge from the Si_1−xGe_x channel into interfacial Si layers, 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 Si_1−xGe_x layers.