Oxygen in Ge crystals grown by the B2O3 encapsulated Czochralski method

Local vibrations of oxygen in Ge crystals grown by the Czochralski method adopting liquid-B2O3 encapsulation and GeO2 powder doping were investigated by Fourier-transform infrared spectroscopy. Strong absorption peaks at 855cm−1, originating in local vibration of interstitially dissolved oxygen Oi as Ge–Oi–Ge quasi-molecules, developed depending on the doped amount of GeO2. Similarly, an absorption peak related to the combined vibration of Ge–Oi–Ge was found at 1264cm−1 and the conversion factor from the peak intensity to the oxygen concentration was evaluated to be 1.15×1019cm−2. By prolonged annealing at 350°C an absorption peak developed at 780cm−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 Oi atoms.