Mechanisms influencing ''hot-wire'' deposition of hydrogenated amorphous silicon

Intrinsic hydrogenated amorphous silicon (a-Si:H) has been deposited using a hot tungsten filament in pure silane to drive the deposition chemistry-the ''hot-wire'' deposition method. The electronic and infrared properties of the film have been measured as a function of deposition parameters, leading to three principal conclusions. First, to obtain a high quality material, the Si atoms evaporated from the filament (distance L from the substrate) must react with silane (density n(s)) before reaching the substrate; this requires n(s)L greater than a critical value. Second, radical-radical reactions cause deterioration of him properties at high values of G(n(s)L),(3) where G is the film growth rate; this requires G(n(s)L)3 less than a critical value. Finally, the film quality is a function of G, and as G is increased the substrate temperature must be correspondingly increased to obtain high film quality. By optimizing these parameters, we have produced films with excellent electronic properties (e.g., ambipolar diffusion length >200 nm) at >5 nm/s deposition rate. Based on these insights, formulas are also given for optimizing film properties in multiple-filament geometries and in diluted silane. (C) 1997 American Institute of Physics.