Ab initio modelling of boron related defects in amorphous silicon

Abstract

AbstractWe have modeled boron related point defects in amorphous silicon, using an ab initio method, the Density functional theory‐pseudopotential code Aimpro. The boron atoms were embedded in 64 atom amorphous silicon cubic supercells. The calculations were performed using boron defects in 15 different supercells. These supercells were developed using a modified Wooten‐Winer‐Weaire bond switching mechanism. In average, the properties of the 15 supercells agree with the observed radial and bond angle distributions, as well the electronic and vibrational density of states and Raman spectra. In amorphous silicon it has been very hard to find real self‐interstitials, since for almost all the tested configurations, the amorphous lattice relaxes overall. We found that substitutional boron prefers to be 4‐fold coordinated. We find also an intrinsic hole‐trap in the non‐doped amorphous lattice, which may explain the low efficiency of boron doping. The local vibrational modes are, in average, higher than the correspondent crystalline values (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)