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Capacitance-voltage (CV) spectroscopy of classic metalinsulator-semiconductors (MIS) using insulating oxides as well as highly passivating intrinsic and hydrogenated amorphous silicon ((i) a-Si:H) has been discussed extensively in literature, particularly with regard to photovoltaic applications. Imperfectly passivating as well as thermal or light-induced degraded (i) a-Si:H exhibits a reduced passivation quality and an increased defectbased shunt conductivity. These properties cannot be accounted for by classical CV spectroscopy as described in literature for insulating oxides or highly passivating (i) a-Si:H. To characterize such imperfectly passivating or degraded (i) a-Si:H thin films by CV spectroscopy, the required MIS samples have to be prepared following special design rules. Design rules were defined on the base of electric field FEM investigations and empirically validated. In combination with an adapted approach to calculate the number of defects (ND) CV spectrometry becomes a more reliable analytic tool to describe imperfectly passivating as well as degraded (i) a-Si:H.
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. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)