Conduction properties of a-Si:H n+-i-n+ structures: Analysis taking into account the effects of n+-i space-charge regions.

Abstract

The analysis of I-V characteristics of sandwich a-Si:H ${\mathit{n}}^{+}$-i-${\mathit{n}}^{+}$ structures is performed, taking into account the effects of the ${\mathit{n}}^{+}$-i space-charge regions. This enables the computation of the characteristics from the low-bias-linear to the space-charge-limited current regimes, for arbitrary intrinsic layer thicknesses. In the usual analysis, where the influence of ${\mathit{n}}^{+}$-i interfaces is neglected, a scaling law is expected to hold for thick enough i layers. In the present work, the validity of this law is checked as a function the Fermi-level density of states (DOS). For instance, it is found that the scaling law does not hold for a 4-\ensuremath{\mu}m-thick i layer with a ${10}^{15}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$${\mathrm{eV}}^{\mathrm{\ensuremath{-}}1}$ Fermi-level DOS. The I-V measurements on a set of four samples of various thicknesses and a single intrinsic material quality are fairly well described by the model, using a unique Fermi-level DOS value and slope. These two parameters are strongly constrained by the requirement to describe simultaneously the I-V measurements on thin and thick samples.