Properties of a new a-Si:H-like material: Hydrogenated polymorphous silicon

A new a-Si:H-like material has been obtained in a radio frequency-powered plasma-enhanced chemical vapor deposition system (RF-PECVD). This material prepared with dilution of silane into He or H₂, under high total pressure (≈ 132 Pa) and high RF power exhibits enhanced electronic transport properties. The room temperature electronic mobility-lifetime product is increased by a factor up to 200 compared to hydrogenated amorphous silicon (a-Si:H) prepared under standard deposition conditions (lower pressure, lower RF power). The density of states measured by modulated photocurrent and the deep defect density measured by the constant photocurrent method are both less than that of standard a-Si:H. These transport properties are linked to the structure of this new material deposited under conditions close to those for powder formation. This structure seems to result in a decrease of the deep defect density and capture cross sections.