Optical spectra of crystalline silicon particles embedded in an amorphous silicon matrix

Deuterated amorphous silicon films deposited by DC reactive magnetron sputtering were measured by Raman spectroscopy and TEM imaging. The films were found to consist of silicon crystallites embedded in an amorphous silicon matrix. The sub-band-gap optical spectra of these films were recorded using photocapacitance and transient photocurrent spectroscopy. These spectra reveal an amorphous silicon sub-band-gap spectrum together with a unique optical transition in the embedded c-Si particles. This transition corresponds to valence band electrons being optically inserted into empty levels lying within the amorphous silicon mobility gap. We believe these empty levels are associated either with the conduction band of the c-Si particles or with defect states at the crystalline-amorphous boundary. (C) 1998 Elsevier Science B.V. All rights reserved.