Electronic transitions associated with small crystalline silicon inclusions within an amorphous silicon host

Amorphous silicon films were prepared by de reactive magnetron sputtering u nder a range of hydrogen or deuterium partial pressures approaching the pha se transition to full microcrystallinity. Tunneling electron microscopy ima ging indicated that these films consisted of 5-50-nm-sized Si crystallites embedded in an amorphous silicon matrix. The sub-band-gap optical spectra o f these films were recorded using photocapacitance and transient photocurre nt spectroscopy. These spectra appear to consist of a superposition of a su bband-gap spectrum typical of amorphous silicon together with a unique opti cal transition, with a very large optical cross section, corresponding to v alence-band electrons being optically inserted into empty levels lying with in the amorphous silicon mobility gap. We believe these empty levels are as sociated with defect states at the crystalline-amorphous boundary. [S0163-1 829(99)08331-9].