Quantum Size Effects in Multilayer Si-Ge Epitaxial Heterostructures

Abstract

A technology of epitaxial growth was developed making it possible to prepare monolayer and multilayer Ge nanocluster structures of different size and distribution density over silicon or oxidized silicon substrates. A stable field electron emission was obtained from Ge on Si quantum dot structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well, manifesting in such a way the effects of energy quantization in the Ge quantum dots. Moreover, the field emission current showed a considerable photosensitivity in the wavelength range from 0.4 to 10 μm. Besides that, lateral photoconductivity spectra from the same structures revealed anomalous red shifts of the photocurrent excitation spectra to the boundary of about 0.3 eV, which shifted distinctly to lower energies as the number of Ge quantum dot layers increased. A pronounced correlation between these effects suggests a mechanism of the electron transport in Ge quantum dot structures involving the localized energy levels that appear near the band verges due to energy quantization effects.