The quantum levels of self-assembled Ge quantum dots are studied by photocurrent spectra and admittance spectra. The photocurrent peaks appearing around 0.8 eV are ascribed to the indirect transition of the carriers from the quantum level in Ge dots to the conduction band of Si. The activation energies derived from the admittance spectra under different bias voltages are in the range of 0.257-0.356 eV, which indicates that the ground hole state in Ge dots of 40 nm in diameter is about 0.36 eV, and the Coulomb charging energy in this kind dots is about 10 meV. (C) 2003 Elsevier Science Ltd. All rights reserved. References: 11
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