Oxygen in Ge crystals grown by the B ₂O ₃ encapsulated Czochralski method

Local vibrations of oxygen in Ge crystals grown by the Czochralski method adopting liquid-B ₂O ₃ encapsulation and GeO ₂ powder doping were investigated by Fourier-transform infrared spectroscopy. Strong absorption peaks at 855 cm ^-1, originating in local vibration of interstitially dissolved oxygen O _i as Ge-O _i-Ge quasi-molecules, developed depending on the doped amount of GeO ₂. Similarly, an absorption peak related to the combined vibration of Ge-O _i-Ge was found at 1264 cm ^-1 and the conversion factor from the peak intensity to the oxygen concentration was evaluated to be 1.15×10 ¹⁹ cm ^-2. By prolonged annealing at 350 °C an absorption peak developed at 780 cm ^-1, indicating formation of oxygen-related thermal donors. From the variations of carrier density and oxygen concentration, one donor was found to possess about 15 O _i atoms.