INPLANE PHOTOCONDUCTIVITY IN AMORPHOUS-SILICON DOPING MULTILAYERS

We prepared amorphous Si p-i-p-i and n-i-n-i doping multilayers to stu dy their in-plane carrier transport and interfacial defect densities. The structures were grown using glow discharge or electron-cyclotron-r esonance-enhanced chemical vapour deposition. We measured the followin g: composition by secondary-ion mass spectrometry; transport by dark c onductivity sigma(d) and its thermal activation energy, by continuous- wave photoconductivity sigma(ph) as a function of intensity and wavele ngth, and also by photoconductive decay; defect density by phototherma l deflection spectroscopy (PDS) and the constant-photocurrent method ( CPM). sigma(d) is dominated by the doped layers. The intensity depende nce of sigma(ph) suggests that it also is controlled by the doped laye rs. The fast component of the photoconductivity response time is compa rable with that of the doped bulk. The PDS spectra of the multilayers are nearly identical with those of the bulk doped hydrogenated amorpho us 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 propor tional to the number of interfaces.