Near-surface regions in hydrogenated amorphous and microcrystalline Si were probed by recording the transient photo-current after application of a green laser pulse with short absorption depth through the glass-substrate/Si interface. Depending on the spatial defect inhomogeneity close to the illuminated surface the transient photo-current showed a different decay behaviour under strongly absorbed green light as compared with more uniformly absorbed red illumination. A Fourier transform technique was applied to the photo-current decay, which revealed spatial inhomogeneities in the deep-defect density in amorphous Si. For a highly crystalline sample of microcrystalline Si, a depth homogeneity was found in the electronic properties; in agreement with information from structural investigations.

Depth Profiling in Amorphous and Microcrystalline Silicon by Transient Photoconductivity Techniques. R.Brüggemann, C.Main, S.Reynolds: Journal of Physics - Condensed Matter, 2002, 14[28], 6909-15