In-plane photoconductivity in amorphous silicon doping multilayers

We prepared amorphous Si p-i-p-i and n-i-n-i doping multilayers to study their in-plane carrier transport and interfacial defect densities. The structures were grown using glow discharge or electron-cyclotron-resonance-enhanced chemical vapour deposition. We measured the following: composition by secondary-ion mass spectrometry; transport by dark conductivity sigma(d) and its thermal activation energy, by continuous-wave photoconductivity sigma(ph) as a function of intensity and wavelength, and also by photoconductive decay; defect density by photothermal deflection spectroscopy (PDS) and the constant-photocurrent method (CPM). sigma(d) is dominated by the doped layers. The intensity dependence of sigma(ph) suggests that it also is controlled by the doped layers. The fast component of the photoconductivity response time is comparable with that of the doped bulk. The PDS spectra of the multilayers are nearly identical with those of the bulk doped hydrogenated amorphous silicon. The pronounced wavelength dependence of sigma(ph) renders CPM sensitive to the i layer plus the p-i or n-i interfacial defects. The interfacial defects are produced by dopants carried over from the doped to the i layers. Their area density in the multilayers is proportional to the number of interfaces.