Experimental Determination of the Dark Fermi Level in Hydrogenated Amorphous Silicon.

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Abstract
The position of the dark fermi level in hydrogenated amorphous silicon (a-Si:H) is important in determining its electrical properties and is a key parameter in the detailed modelling of materials and devices. The activation energies of conductivities have been investigated on intrinsic a-Si:H films from various laboratories where the slopes of the Arrhenius plots have ranged from 0.27 eV to 0.87 eV. In many cases, marked differences are found between the results obtained from two and four probe measurements, highlighting the importance of the four probe configuration. Results are presented which help to explain the scatter in the measured activation energies between intrinsic films of a-Si:H. Differences in the activation energies are discussed in terms of current limiting processes which act in series with the material bulk resistance. It will be shown that the conductivity of the film and the contact are key factors in assessing whether the position of the fermi level can be accurately determined from a two contact measurement.