Influence of annealing and Hydrogen content on structural and optoelectronic properties of Nano-multilayers of a-Si:H/a-Ge: H used in Solar Cells

Abstract

Nano-multilayers (NMLs) of a-Si:H/a-Ge: H were prepared at 200◦C by alternating deposition from SiH4 and GeH4 plasmas in a computer-controlled four chamber glow-discharge deposition system with capacitive coupled diode reactors. IR spectroscopy and scanning electron microscope (SEM) were used to study the structural changes after annealing at 300 and 450oC for 8 h. The annealed multilayers exhibit surface and bulk degradation with formation of bumps and craters. The electrical measurements results reveal that the increase of electrical conductivity, while optical energy gap is decreased with increasing the annealing temperature and/or time is partially due to formation of H bubbles in the Ge layers and partially due to crystallization effects. On the other hand it was found that the activation energy of crystallization deduced from the annealing time dependence of the conductivity using Avrami's equation is structural dependent.