A UNIFIED RELATIONSHIP AMONG THE OPTOELECTRIC PROPERTIES OF A-SI-H AND APPROACHES FOR FURTHER IMPROVEMENT

The optical, electric and structural properties of hydrogenated amorphous silicon (a-Si:H) films, deposited using the plasma-CVD method, are systematically investigated as functions of the substrate temperature (T(s)) and plasma parameters such as the RF power, gas pressure, and the dimensions of the reactors in order to optimize their properties for solar cells. Those properties are successfully controlled over a wide range by the plasma parameters at a fixed T(S). The decrease in the film deposition rate and the increase in the T(S) have practically identical effects on the properties of a-Si:H in this study. The experimental results suggest that the properties of a-Si:H films are governed by a competition between the rate of film growth and the rate of thermally-activated surface reactions at or near the film-growing surface during film deposition. Limitation in the controllability of 'device-quality' a-Si:H can be overcome by diluting SiH4 with hydrogen or helium at low T(S), or by hydrogen-plasma treatment of a-Si:H. The present results provide a guide for further improvement in the characteristics of a-Si:H for the photovoltaic layer of solar cells.