Influence of Hydrogen content on structural and optical properties of doped nano-a-Si:H/a-Ge: H multilayers used in solar cells

Abstract

Doped-nanomultilayers of a-Si:H/a-Ge:H thin films are used as a new type of narrow band gap materials for amorphous silicon–based solar cells. High efficiency solar cells are necessary to convert solar energy to electrical energy at low cost until. Doped-nanomultilayers 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 capacitively coupled diode reactors . IR, XRD and SEM were used to study the structural changes after annealing at 300 for 8 h. The annealed doped-nanomultilayers exhibit surface and bulk degradation with formation of bumps and craters. The measurements results reveal that the 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.