Self-assembled Ge Quantum Dots Research Articles

Erratum: Coulomb Charging Effect in Self-Assembled Ge Quantum Dots Studied by Admittance Spectroscopy [Phys. Rev. Lett. 80, 3340 (1998)

Received 10 February 1999DOI:https://doi.org/10.1103/PhysRevLett.82.2622©1999 American Physical Society

Intersubband absorption in boron-doped multiple Ge quantum dots

The intersubband absorption in self-assembled boron-doped multiple Ge quantum dots is observed. The structures used consist of 20 periods of boron-doped Ge dot layers and undoped Si barriers. The infrared absorption as a function of wavelength is measured by Fourier transform infrared spectroscopy using a waveguide geometry. Absorption peaks in the mid-infrared range have been observed, which are attributed to the transitions between the first two heavy hole states of the Ge quantum dots. The polarization dependence measurement is used to study the nature of the transitions. This observation suggests the possible use of multiple Ge quantum dots for infrared detector application.

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.

Coarsening of Self-Assembled Ge Quantum Dots on Si(001)

The size distribution of self-assembled heteroepitaxial islands is critical to their application as quantum dots in novel devices. In situ, real time UHV transmission electron microscopy studies of Ge island growth on Si(001) show that island coarsening occurs even during growth. With increasing volume, a shape transition from pyramids to domes gives rise to an abrupt change in chemical potential. This leads to a bifurcation in the size distribution and ultimately to a narrow size range. Simulations of coarsening in the presence of a shape transition are in good agreement with experimental results.

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

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.