Mobility–lifetime estimates in amorphous hydrogenated silicon (a-Si:H)

Abstract

Estimates of the majority photocarrier mobility–lifetime (μτ) product obtained from time-of-flight transient photoconductivity and from steady-state photoconductivity are compared. It is shown that in principle both experiments measure the integral of the transient drift mobility; the demonstration is based solely on linear response theory and is independent of the specific microscopic transport and recombination model. Estimates of μτ for undoped amorphous hydrogenated silicon (a-Si:H) based on the two techniques disagree by a factor of approximately 100 in comparable specimens. Possible origins of the discrepancy are discussed in relation to experimental procedures, optical bias effects and surface inhomogeneity. It is concluded that in undoped a-Si:H the dangling-bond defect observed in electron-spin resonance acts predominantly as a photocarrier trap and not as a simple recombination centre.