Preparation and optical absorption of InSb microcrystallites embedded in SiO₂ thin films

Semiconductor InSb microcrystallites embedded in SiO₂ thin films were prepared by the radio-frequency cosputtering technique. The structures of the thin films were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The average size of the microcrystallites, depending on post-annealing temperature and time, is on the order of a nanometer. The absorption spectra of the films were measured and large blue shifts of the absorption edge were observed in a wide range from the ultraviolet to the infrared spectral regime. The blue shifts were attributed to the strong quantum confinement effect and explained qualitatively in terms of the effective-mass approximation. A large discrepancy between the theory and our experimental results was found and discussed, particularly considering the change of the effective mass of exciton in the InSb microcrystallites.