Low frequency noise in hydrogenated p-type amorphous silicon thin films

We report on electrical noise measurements of p-type a-Si:H thin films prepared by plasma enhanced chemical vapor deposition. Samples were grown at various boron concentrations and hydrogen dilution of the silane precursor. Measurements were made at temperatures ranging from 210K to 450K. In this temperature range, Mott variable range hopping conduction describes the electrical conductivity, and the noise has a 1/fγ component. The exponent γ for temperatures below 400K is approximately 1, and the noise follows the Hooge model. For temperatures between 240K and 380K, the 1/f noise was found to be independent of the conductivity. Therefore, the carrier concentration does not change appreciably with temperature and the change in conductivity is due to the temperature dependence of the hole mobility. The normalized Hooge parameter correlates with the Mott hopping parameter, T0M, and in turn, to the material dopant boron concentration and hydrogen dilution levels. For temperatures above 400K, the frequency exponent, γ, is larger than 1, indicative of a generation-recombination trap contribution to the noise. From the dependence of the normalized Hooge parameter to the Mott characteristic temperature T0M, we conclude that the electrical 1/f noise in p-type a-Si:H is associated with hopping conduction.