Evolution of microstructure and incorporation of excess hydrogen during the growth of hydrogenated polymorphous silicon at high rate

Abstract

Hydrogenated polymorphous silicon (pm-Si:H) is a material consisting of a small volume fraction of nanocrystals embedded in an amorphous matrix, and which can be grown at high deposition rates by increasing the radio-frequency power. When grown at high deposition rates, pm-Si:H films show a shift of their infrared (IR) absorption stretching band peak to higher wavenumbers and a sudden increase in their optical bandgap. The IR absorption spectrum was analyzed by deconvolution into three bands, including a medium stretching mode positioned at 2030 cm-1, which has been attributed to Si-H bonds at silicon nanocrystal surfaces. Secondary ion mass spectrometry measurements confirmed that an excess of hydrogen is incorporated in pm-Si:H grown at high deposition rate, leading to a sharp increase in the optical bandgap. We suggest that this sharp increase can be used as a simple tool to detect the deterioration of material quality when using high deposition rate processes.