Depth profiling in amorphous and microcrystalline silicon by transient photoconductivity techniques

We probe near-surface regions in hydrogenated amorphous andmicrocrystallinesilicon by recording the transient photocurrent after application of a green laserpulse with short absorption depth through the glass-substrate/silicon interface.Depending on the spatial defect inhomogeneity close to the illuminatedsurface the transient photocurrent shows a different decay behaviour understrongly absorbed green light as compared with more uniformly absorbed redillumination. We apply a Fourier transform technique to the photocurrent decay,which reveals spatial inhomogeneities in the deep-defect density in amorphoussilicon. For a highly crystalline sample of microcrystalline silicon we find depthhomogeneity in the electronic properties, in agreement with information fromstructural investigations