THE QUASI-NEUTRALITY CONDITION IN AMORPHOUS-SEMICONDUCTORS - REFORMULATION OF THE LIFETIME RELAXATION CRITERION/

The concepts of lifetime and relaxation semiconductors introduced by v an Roosbroeck and Casey are reconsidered for amorphous semiconductors and the effect of localized states on the lifetime/relaxation criterio n specified: The quantity to be considered is tau(rho)/T-d, where T-d is (as before) the dielectric relaxation time, but tau(rho) is now the lifetime of the total charge a including charge stored in localized s tares. tau(rho) is equal to the free carrier lifetime times a correcti on factor that is much larger than unity for amorphous semiconductors. Bandtail states and dangling bonds act differently on the criterion. The correction factor is frequency-dependent and decreases at higher f requencies. Two illustrative experimental examples (low substrate temp erature a-Si:H, a-SiC:H alloys) are given, showing borderline casts.