The role of dangling bonds in the transport and recombination of a-Si: Ge: H alloys

Measurements are reported of the luminescence, time-of-flight photoconductivity and electron spin resonance (ESR) in a-Si: Ge: H alloys. In the alloys it is found that the luminescence intensity varies with defect density according to a tunnelling model similar to that in a-Si:H. However, the tunnelling distance decreases with Ge concentration up to about 30% and then increases. This nonmonotonic behaviour is attributed to the additional chemical disorder of the alloys. Time-of-flight experiments confirm that the dangling bonds are the dominant deep trap in the alloys. We find that the capture cross-sections for electrons and holes are very similar to those measured in a-Si: H, and are independent of whether the trap is a Ge or Si dangling bond.