Transient mobility and lifetime studies in amorphous silicon and their interpretation

Abstract

This paper begins with a brief review of the contributions which transient experiments on crystalline and amorphous solids have made to the understanding of transport properties in these materials. The main part of the paper is concerned with three topics arising from recent work on amorphous silicon junctions. §2 deals with the problem of deducing the extended-state electron mobility from drift mobility results on the basis of the multi-trapping model. The analysis of new high-temperature drift mobility data removes ambiguity in the interpretation and leads to an excellent fit over the complete temperature range from 150K to 450K. The second topic is the study of excess carrier lifetimes by transient methods. Experiments on a series of doped junctions show the pronounced sensitization and de-sensitization of the majority and minority carrier lifetimes respectively. The results can be given a quantitative interpretation in terms of the occupation statistics of the dangling-bond centre, and the D⁰ state is shown to lie between 0·95 eV and 1·00eV below E _c. Thirdly, we discuss the temperature dependence of the μτ product for electrons which is directly related to the capture cross-section σ. It is shown that for capture into the neutral D⁰ centre, σ₀(T) decreases with increasing T, consistent with the expected multi-phonon emission process. On the other hand, interaction with the Coulombic D⁺ centre leads to the opposite temperature dependence for σ₊(T).