Photo-thermoelectric power of a-Si as a function of incident wavelength

Abstract

Measurements have been made at room temperature of the thermoelectric power as a function of illumination wavelength on undoped and boron doped films. During these measurements the intensity of the light was increased as the incident photon energy was decreased in such a way that the photocurrent would have remained constant. Results show that in the photon energy range 1–3 eV photocarrier transport takes place predominantly through one conduction path and the position of the quasi Fermi level relative to that conduction path remains invariant for both undoped and p-type specimens. One of the more important assumptions of the constant photocurrent method is that carrier lifetime is independent of photon energy. The results confirm this assumption for measurements on amorphous silicon films in the photon energy range investigated but bring into question the usual interpretation of the Urbach edge for p-type material.