Role of hydrogen surface coverage during anodic plasma deposition of hydrogenated nanocrystalline germanium

Abstract

Nanocrystalline Ge:H films were deposited on the anode of a conventional plasma-enhanced chemical vapor deposition system using highly H2-diluted GeH4 as source gas. The structural changes with substrate temperature, hydrogen dilution, and rf power were investigated by x-ray diffraction and Raman scattering. The hydrogen content and H bonding configuration were determined by infrared absorption spectroscopy. It was found that increased rf power mainly favors nucleation of grains while increased H2 dilution mainly favors the subsequent growth of grains. Transitions from an amorphous to a crystalline and then back to an amorphous phase are observed as the substrate temperature is increased. The amorphous phase at high temperatures and variations in the preferred crystallite orientations are explained by changes in the diffusion length of adsorbed precursors due to changing hydrogen coverage on the growing surface.