In this study, we discuss measurements of the J-Vcharacteristics of an a-Si : H n(+)-i-n(+) structure, and the results of numerical simulation using the AMPS-1D simulation program. Application of the AMPS simulation model to the sample structures considered allows us to determine the structural properties of the a-Si:H n(+)-i-n(+) structure. The one-dimensional simulation program was examined in n(+)-i-n(+) structures with different qualities and thicknesses of the i-layer. We find that the n(+)/i interface is more abrupt for a device with a high density of states (DOS), resulting in high values of the activation energy (E-act). In contrast, thin samples of good quality (low DOS) give low values of Eat. Analysis by numerical modeling confirms the experimental results. (C) 2003 Kluwer Academic Publishers.