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Modélisation ab initio des défauts ponctuels liés au bore dans le silicium amorphe

T. Á. Oliveira; University of Aveiro (2011)

Abstract

The main goal of the current work is to model boron related point defects in amorphous silicon, using an ab initio method, the Density functional theory-pseudopotential code (AIMPRO).

The boron complexes were embedded in 64 silicon atom supercells. We have investigated the boron defects in 15 different supercells. These supercells were developed using a Wooten-Winer-Weaire bond switching mechanism by Ribeiro et al. (2010). 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.

To be confident with the method, the simplest boron defects and the self-interstitial in crystalline silicon were modeled. The main conclusions are in line with other authors’ work.

In amorphous silicon it has been very hard to find a real self-interstitial, since for almost all the tested configurations, the amorphous lattice relaxes overall. We find 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, as advanced by Santos et al. (2010). The local vibrational modes are, in average, higher than the correspondent crystalline values.