Electronic transport properties of low band gap a-SiGe:H alloys prepared by PECVD technique

The electronic transport properties of a-(Si,Ge):H alloys across the range of Ge content (0-40%) grown using PECVD technique have been investigated in detail by employing the microwave photomixing technique. Strong evidence for the existence of long-range potential fluctuations in a-(Si,Ge):H alloys has been found from the measurements of electric field dependence of the drift mobility. It was observed that the film transport properties degrade monotonically with increasing Ge content, where the strongest potential fluctuations occur as a result of a significant increase in the charged defect density. The potential fluctuations whose effect is enhanced by adding Ge to the alloy system result in deterioration of the transport properties of a-(Si,Ge):H alloys. Our present results demonstrate that the increased charged scattering centers and compositional disorder upon adding Ge to the alloys play an important role in the potential fluctuations.