Systematic Errors in the Analysis of the Infrared Transmission Data Of Hydrogenated Amorphous Silicon

Abstract

ABSTRACTThe validity of the Brodsky, Cardona and Cuomo (BCC) [1] and the Connell and Lewis (CL) [2] methods to analyze infrared transmission data of hydrogenated amorphous silicon (a-Si:H) was examined using computer simulations. Transmission spectra for a-Si:H films 0-5¼m thick and containing up to 30 atomic% hydrogen were simulated assuming coherent reflections in the film and incoherent reflections in the c-Si substrate. Analysis of the simulated data for the 640cm−1 Si-H wagging mode shows that the BCC and CL techniques systematically overestimate the absorption coefficeint, α, and hence hydrogen content, CH, when the film thickness, d, is less than ∼l¼m. The error is nearly independent of CH and is as large as 80% in the limit d→0. On this basis, previously reported experimental evidence for the dependence of CH on d is shown to be an analysis artifact. A simple method to correct the hydrogen content determined by the BCC or CL analysis using only the film thickness is presented.