EFFECT OF HYDROGEN ON FRENKEL-PAIR ANNIHILATION IN SILICON - A QUANTUM-CHEMICAL STUDY

Energy barriers for Frenkel pair formation and annihilation in a hydro gen-saturated silicon lattice are calculated using the technique of th e self-consistent field of molecular orbitals with linear combination of atomic orbitals (SCF MO LCAO), partially neglecting diatomic differ ential overlap (NDDO) of the energy barriers, which must be overcome t o form Frenkel pairs and to annihilate them in a hydrogen-saturated si licon lattice. The calculations were carried out for the optimized geo metries of an ideal Si crystal, a cluster with a vacancy, and a cluste r with a vacancy and different numbers of hydrogen atoms. It is shown that 1) near a vacancy site, hydrogen is preferentially localized as a second-nearest neighbor, 2) the availability of hydrogen near a vacan cy results in a dramatic lowering of the potential barrier for Frenkel -pair annihilation, and 3) the height of the potential barrier is sign ificantly affected by the charge state of the hydrogen (H-0, H+, H-). The degree of lattice relaxation near the vacancy is determined as a f unction of the presence of hydrogen and as a function of its charge st ate. The calculations support the proposed model of enhanced annealing of vacancy defects in silicon with oxygen and agree with the well-kno wn experimental results. (C) 1996 American Institute of Physics.