Measurements of Confined Energy Levels and Coulomb Charging Effect in Self-Assembled Ge Quantum Dots by Admittance Spectroscopy

Abstract

AbstractWe perform measurements of the discrete quantum energy levels and Coulomb charging of self-assembled Ge quantum dots imbedded in Si barriers by using the admittance spectroscopy technique that was originally developed to measure the defect levels of bulk materials and the band offsets of heterojunctions. By varying the bias voltage, the population of carriers in the dot changes and the Coulomb charging effect could be clearly seen from the step-like change of the activation energy for hole emission in the admittance spectra. Up to five holes charged in a Ge dot with a lateral dimension of 13nm is observed. The energy levels of ground state and first excited state are determined. The advantages of this method are the relatively high measuring temperature, large signal to noise ratio, and its simple and straightforward use and interpretation. The requirement on the uniformity of the dot size distribution of the sample is quite tolerant.