Ab‐initio modeling of a‐Si and a‐Si:H

Abstract

AbstractThe simulation of a‐Si is complicated because there is no direct experimental data, as there are for crystals. Our approach to simulate a‐Si is to build several relatively small amorphous samples and, later, the properties we wish to calculate are averaged over all samples. We applied the Wooten, Winer and Weaire bond switch to 64 atom cubic supercell of crystalline silicon. This mechanism was used to create 15 samples of continuous random network of silicon. For each supercell, the volume and atomic relaxation were allowed in order to minimize the total energy, using a density functional‐pseudopotential code. The radial and angular distributions, the electronic and vibrational density of states, and the Raman spectra were calculated. The radial distribution agrees very well with experimental data. The angular distribution has its maximum at 109.4 degree. The experimental positions and relative intensities of the Transverse Optical (TO) and Transverse Acoustic vibrational modes are well reproduced, with 14 and 25 cm‐1 peak deviations, respectively. The shape of the calculated Raman spectra agrees well with experimental data, being the intense TO peak shifted by 50 cm‐1. The TO width at half‐weight is very well reproduced. Introducing hydrogen in the a‐Si samples, decorating all the undercoordinated Si atoms and at bond centres of floating bonds, the hydrogen vibrational frequencies of the relaxed structures agree very well with experimental data. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)