The effect of aging on the dark conductivity and noise in hydrogenated microcrystalline silicon thin films

Abstract

Aging hydrogenated microcrystalline silicon in air is found to affect both the dark conductivity and the 1/f noise. For a sample with a crystalline volume fraction of 0.39, the conductivity decreased by three orders of magnitude at 20 degrees C after short-term (10-20 hrs) exposure to air. The conductivity recovered after annealing to 160 degrees C. Long-term exposure (2 years) resulted in a permanent decrease by a factor of 16 at 20 degrees C even after annealing. Long-term aging also increased the conductivity activation energy from 0.193 eV to 0.342 eV. After short-term aging and below the annealing temperature, the conductivity prefactor sigma(0) and the activation energy E-sigma follow a Meyer-Neldel type of relation. Conductance fluctuations measured for annealed and aged states show all the expected characteristics of 1/f noise. The spectra fit a power law with slope -1; the slope is not affected by temperature or aging. The magnitude of the noise decreases with temperature after aging, but by much less after annealing. A simple analysis of the product of conductivity and noise magnitude can be used to estimate the free carrier mobility. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim