Coulomb Charging Effect in Self-Assembled Ge Quantum Dots Studied by Admittance Spectroscopy

Quantum confined energy levels and the Coulomb charging effect of holes in self-assembled Ge dots embedded in Si barriers are studied using admittance spectroscopy at temperatures above 100 K. Ground state and first excited state occupancies of five to seven holes are identified by varying the Fermi-level position under different applied bias voltages in the admittance measurements. Hole-capture cross sections of the quantum levels are found to be extremely large and energy dependent.