Growth of Germanium Carbon Alloy by Pecvd Using Silane as a Growth Promoter

Abstract

A possible alternative to a-SiGe for use in multijunction solar cells is a-GeC alloy. Only preliminary work has been done so far on this alloy, Mostly for use as an IR anti-reflection coating, with little study done on its optoelectronic properties. GeC films were grown by the PECVD Method from a novel gas mixture using GeF₄ as the germanium source gas. Methane was used as the carbon source, with H₂ being added for additional hydrogenation of the film. It was found that adding silane to the mixture would increase the growth rate from less than 1 Å/s up to 30 Å/s. The films contained no detectable silicon, even at mixture ratios of five SiH₄ to one GeF₄. Varying the amount of methane in the gas mixture allowed the film optical bandgap to be adjusted from 1.1 eV to 1.8 eV. The effect of other parameters such as RF power level and H₂ flow rate on bandgap and growth rate were also explored. Optoelectronic properties in the 1.2 to 1.4 eV bandgap range will also be reported.