Thermopower and Hall‐effect investigations of microcrystalline silicon films

Abstract

A series of phosphorous doped microcrystalline silicon (μ c‐Si:H) and amorphous silicon (a‐Si:H) samples with different degrees of crystallinity was prepared using plasma enhanced chemical vapour deposition (PECVD). Thermoelectric power, Hall‐effect and electrical conductivity measurements were made in the temperature range 80–430 K. The crystallinity of the samples was determined by Raman measurements. The results show that the charge carrier concentration as determined by Hall‐effect and conductivity is highest and the absolute values of the thermopower are lowest at a medium magnitude (38–74%) of crystallinity.Moreover, the effective density of states at the conduction band was calculated for different temperatures by combining Hall, conductivity and thermopower measurements. At room temperature we get results close to the value for crystalline silicon by using only the crystalline amount of the microcrystalline sample and a heat of transport term of AC = 3.1. For the amorphous material, the data suggest that the Hall mobility (measured with an anomalous sign) underestimates the charge carrier mobility (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)