Interface-structure Dependent Confining Potential Height and Quantized Energy of Ge Nanodots Fabricated onto the Oxidized Si Substrate

Abstract

Quantum confinement effect in the valence band of Ge nanodots, fabricated onto an ultrathin SiO2 film on Si(111) substrate, was clearly measured by means of photoemission spectroscopy. Dot-size dependent shifts of the highest occupied state were well described by quantized energy levels of confined holes by the spherical parabolic potential. Two-types of Ge nanodots with different interface conditions, named as ‘epitaxial’ and ‘non-epitaxial’, can be fabricated depending on the growth temperature. The actual confining potentials for the quantum states in the two-types of Ge nanodots were evaluated, which clearly indicates drastic reduction of the confining potential barrier height for the epitaxial dots owing to voids formed in the interface SiO2 layer just below the Ge nanodots.