Many optical absorption peaks observed in electron-irradiated n-type Si

Abstract

The properties of many optical absorption peaks in electron-irradiated n-type Si crystals were studied. Specimens were prepared from various Si crystals. After chemical etching, they were irradiated with 3 MeV electrons at room temperature (RT). Their optical absorption spectra were measured with a Fourier transform infrared spectrometer at temperatures in the range of 7 K to RT with a resolution of 0.25 cm−1. Many optical absorption peaks were observed in the wave number range between 850 and 1600 cm−1 only in n-type (phosphorus-doped) Si crystals. Hence, they are due to donors. Such peaks were very weak 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 the very high concentration of oxygen in those crystals. They disappeared as the result of annealing at above 175 °C. Temperature dependencies of intensities of various peaks were studied.