Transient photocurrents as a spatially resolved probe of carrier transport and defect distributions in silicon thin films

Highlights: ► Transient photocurrents were measured in amorphous and microcrystalline silicon. ► The electronic density of states was calculated from photocurrent transients. ► A computer model confirmed depth-dependence with laser pulse wavelength. ► In amorphous silicon light-soaking modifies the electronic defect profile. ► In microcrystalline silicon a seed layer modifies growth correlated to defect density. -- Abstract: Transient photocurrent spectroscopy (TPC) yields the energetic distribution of localised states in disordered semiconductors from an analysis of the decay of photocurrent with time following a short laser pulse. By comparing results at different laser excitation wavelengths, and hence absorption depths, information on spatial non-uniformities may also be inferred. Here we investigate the use of TPC as a spatial probe with reference to two thin-film silicon systems; amorphous silicon subjected to various light-induced degradation regimes, and microcrystalline silicon grown on a range of 'seed' layers. Computer simulation is used to support experimental findings, and to identify sensitivity and resolution limitations