Optical absorption peaks observed in electron-irradiated n-type Si

Abstract

We found many optical absorption peaks in electron-irradiated n-type Si crystals. Specimens were prepared from various Si crystals. After chemical etching, they were irradiated with 3-MeV electrons at RT. Their optical absorption spectra were measured with an FT-IR spectrometer at temperatures in the range of 5 K and RT with a resolution of 0.25 cm −1. Many optical absorption peaks were observed in the wavenumber range between 950 and 1600 cm −1 only in n-type (phosphorus-doped) floating-zone grown Si crystals. Hence, they are due to donors. They were not observed in Czochralski-grown Si (CZ-Si) crystals. This suggests that these peaks are due to complexes of phosphorus and vacancies since most vacancies in CZ-Si form pairs (A-center) with oxygen because of very high concentration of oxygen. They disappeared by annealing at above 200°C.