CHARGE-TRANSPORT IN MICROCRYSTALLINE SILICON FILMS

We prepared a series of nominally undoped microcrystalline silicon (mu c-Si:H) films in a conventional radio frequency plasma enhanced chemi cal vapor deposition reactor from silane diluted with hydrogen. To inv estigate the transport mechanism we carried out measurements of the da rk conductivity, sigma(d), Hall mobility, mu(H), and thermoelectric po wer, S, in the temperature range 200 to 450 K. The activated temperatu re dependences of mu(H) and of a quantity, Q, derived from ab and S in dicate that the transport properties are determined by an inhomogeneou s distribution of the charge carriers (electrons). We analyze our resu lts in terms of two models. The first one assumes potential barriers, not at the grain boundaries but at the interfaces of the columns which are typical for mu c-Si:H. In the second model inhomogeneously distri buted charged centers give rise to potential fluctuations. Both models can equally well account for our experimental data. (C) 1998 Elsevier Science B.V. All rights reserved.