Microscopic structure of the hydrogen-boron complex in crystalline silicon.

Abstract

The microscopic structure of hydrogen-boron complexes in silicon, which result from the passivation of boron-doped silicon by hydrogen, has been extensively debated in the literature. Most of the debate has focussed on the equilibrium site for the H atom. Here we study the microscopic structure of the complexes using parameter-free total-energy calculations and an exploration of the entire energy surface for H in Si:B. We conclusively show that the global energy minimum occurs for H at a site close to the center of a Si-B bond (BM site), but that there is a barrier of only 0.2 eV for movement of the H atom between four equivalent BM sites. This low energy barrier implies that at room temperature H is able to move around the B atom. Other sites for H proposed by others as the equilibrium sites are shown to be saddle points considerably higher in energy. The vibrational frequency of the H stretching mode at the BM site is calculated and found to be in agreement with experiment. Calculations of the dissociation energy of the complex are discussed.