External rf substrate biasing during a-Si:H film growth using the expanding thermal plasma technique

The interchangeability of ion bombardment and deposition temperature during a-Si:H film growth at high deposition rates (10-42 Å/s) by means of the expanding thermal plasma has been studied. The ion bombardment is generated by applying an external rf bias voltage on the substrate. It is shown that the opto-electronic performance of the a-Si:H films improves considerably when a moderate rf substrate bias voltage (∼20-60 V) is applied, i.e. the photo response increases two orders of magnitude up to 106. Furthermore, it is also revealed that the additional energy supplied to the growth surface by the ion bombardment, makes a reduction of the deposition temperature by ∼100°C possible, while preserving good material properties. On the basis of the results obtained, three effects caused by the rf substrate bias can be distinguished: creation of an additional growth flux, a reduction of the void incorporation, and an increase in the vacancy density.