Local vibrational modes of the oxygen-vacancy complex in germanium

Infrared absorption of n-and p-Ge crystals enriched with ¹⁶O and/or ¹⁸O isotopes was studied after irradiation with 6-MeV electrons. Absorption spectra were measured at 10 and 300 K. Along with known bands characteristic of oxygen-containing defects, new lines at 669, 944, and 990 cm^?1 were detected. These bands are annealed at temperatures of 120–140°C; the band at 621 cm^?1, previously related to the vacancy-oxygen complex in Ge, is simultaneously annealed. The bands at 621 and 669 cm^?1 showed identical temperatures (10 → 300 K) and oxygen isotope (¹⁶O → ¹⁸O) shifts. These bands were found to correspond to various charge states of a defect with an energy level near E_v=0.25±0.03 eV. It is assumed that such a defect is the vacancy-oxygen complex (A center). The weak bands at 944 and 990 cm^?1 were identified as combinations of asymmetric stretching modes at 621 and 669 cm^?1 with a symmetric one at 320 cm^?1 for neutral and negative charge states of the A center, respectively.