E center annealing in SiGe: Stability and charge states

We have studied proton irradiated and annealed n-type SiGe with a P dopant concentration in the 1 × 1018 cm−3 range by positron annihilation spectroscopy. The Ge contents in the samples were 10, 20 and 30%. The results show that by annealing the irradiated samples at temperatures 250–350 °C, the Ge content around the E center increases. Based on temperature-dependent and coincidence Doppler measurements, we conclude that the increase in Ge content around the E center pulls down the localized second acceptor state, found in Ge, into the SiGe band gap. This charge transition is observed even in samples annealed at 350 °C, with a considerably higher thermal budget than expected for the complex to anneal completely.