Model based prediction of the trap limited diffusion of hydrogen in post-hydrogenated amorphous silicon

The diffusion of hydrogen within an hydrogenated amorphous silicon (a-Si: H) layer is based on a trap limited process. Therefore, the diffusion becomes a self-limiting process with a decreasing diffusion velocity for increasing hydrogen content. In consequence, there is a strong demand for accurate experimental determination of the hydrogen distribution. Nuclear resonant reaction analysis (NRRA) offers the possibility of a non-destructive measurement of the hydrogen distribution in condensed matter like a-Si: H thin films. However, the availability of a particle accelerator for NRR-analysis is limited and the related costs are high. In comparison, Fourier transform infrared spectroscopy (FTIR) is also a common method to determine the total hydrogen content of an a-Si: H layer. FTIR spectrometers are practical table-top units but lack spatial resolution. In this study, an approach is discussed that greatly reduces the need for complex and expensive NRR-analysis. A model based prediction of hydrogen depth profiles based on a single NRRA measurement and further FTIR measurements enables to investigate the trap limited hydrogen diffusion within a-Si: H. The model is validated by hydrogen diffusion experiments during the post-hydrogenation of hydrogen-free sputtered a-Si. The model based prediction of hydrogen depth profiles in a-Si: H allows more precise design of experiments, prevents misinterpretations, avoids unnecessary NRRA measurements and thus saves time and expense. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim