Defect formation during growth of hydrogenated amorphous silicon

The defects believed to limit the performance of devices fabricated using hydrogenated amorphous silicon are identified as singly occupied dangling bonds. The formation of these defects can be explained on the basis of two distinct models which attribute their occurrence to bulk thermodynamic equilibrium and surface diffusion of precursors during film growth, respectively. We present experimental results on the deposition-rate dependence of electronic and structural properties that are shown to be inconsistent with bulk thermal equilibration. The results, which were anticipated from the surface-diffusion model, are shown to be consistent with the underlying defect-formation mechanism. Simple isotopic substitution of hydrogen is shown to systematically alter the defect-formation rate, providing clear evidence of a surface-controlled defect-formation process during growth of hydrogenated amorphous silicon.