Transient Versus Steady State Measurements on the Transport Properties of a-SI:H Films

Abstract

ABSTRACTTransient and steady-state measurements of the ambipolar diffusion length (L*) in undoped a-Si:H films have been carried out through Flying Spot Technique (FST) and Spectral Photovoltage Technique (SPT) using either Schottky or pin structures. The FST is based on the photovoltage response of a monochromatic light that moves with a constant velocity in the interface direction, while in SPT the optical excitation is achieved by changing the absorption coefficient of the incident light and so, the light depth penetration. In FST the additional photo-effect due to the light spot movement allows to infer separately L* and the effective lifetime, (τ*) while in SPT the curve shape of the spectral response allows to estimate the interface behavior and L*. The obtained results reveal that the transient measurement is useful for determining the transport properties of the bulk while the steady technique seems to be more useful to infer the role of the interface on device performances. Limitations of the above techniques will also be reported.