Interstitial boron and oxygen related defects as the origin of the deep energy level in Czochralski-grown silicon

The structure of the B and O related defect complex in Czochralski (CZ)-grown Si crystal is theoretically studied by using ab initio calculations. When a B-doped CZ Si wafer is used as a solar cell material, light irradiation and/or minority carrier injection causes the solar cell conversion efficiency to be degraded. Because the interstitial B and O complex is considered to be the key defect causing the degradation, the stable position of interstitial B in O-doped Si crystal is determined by ab initio calculations using the Si29B1O1H36 cluster system. Although interstitial B cannot directly create a stable chemical bond with interstitial O, it is found to exist stably as an interstitial B-substitutional Si-interstitial O complex. The interstitial B and substitutional Si atoms in the defect are positively charged and generate a deep energy level, indicating that this complex efficiently attracts an electron due to its electrical force and that it might act as a recombination center. When this complex is generated by light irradiation and/or minority carrier injection, it shortens the lifetime of the electron resulting in the degradation of solar cell performance. (C) 2002 American Institute of Physics.