Transition from diffusive to ballistic capture related to hydrogen incorporation in amorphous silicon

Abstract

Abstract We have shown in previous work that, in triode d.c. sputtered amorphous silicon, the value of the capture cross-section σ of deep gap states depends strongly on the hydrogen content of the material. In this Letter, we analyse the influence of such an effect on the transport properties of a set of samples whose hydrogen content C H varies between 8 and 20%. For this purpose, we have measured at room temperature the mobility–lifetime product for electrons, μnτn, the density of states at the Fermi level N(EF) and the defect density N s derived from photothermal deflection spectroscopy experiments. Log–log plots of the μnτn N(E F) and μnτn N s products against σ show two regimes with a transition corresponding to a hydrogen content of about 12%. These two regimes are related to different modes of capture controlled either by a diffusive process (low C H) or by a ballistic process (high C H). From the transition between the two regimes, we calculate that the electron scattering length is of the order ...