A Basic Study of the GeH4 + H2 RF Discharge

Abstract

ABSTRACTExtensive studies were made of GeH4+H2 and SiH4+H2 rf discharges used in depositing a-Ge:H and a-Si:H films. Residual Gas Analysis (RGA) Measurements were made of the gaseous species generated by these discharges. Data from the measurements of SiH4 + H4 discharges were entirely consistent with the generally accepted models of silane discharge chemistry and a-Si:H film deposition. Identical experiments for GeH4 + H2 discharges show that the chemistry for these discharges cannot be interpreted using a model similar to that proposed for silane. A review of the literature reveals differences between the stability of GeH2 and SiH2 radicals. These differences, usually overlooked by other workers, can account for the observed differences in the RGA results, as well as offer an explanation as to why it is difficult to deposit structurally homogeneous a-Ge:H.Other RGA Measurements and electrode potential measurements are compared to the properties of a-Ge:H films that are deposited under different deposition conditions. Overall, the results strongly suggest that the chemistry which is beneficial for homogeneous film growth is promoted by a high electron temperature in the discharge. This conclusion is shown to be consistent with the results summarized above.