Extended defect states in Ge quantum dots grown by RTCVD

The interface and localized states of Ge-QDs or GeSi-QWs could be considered as giant defect states for recombination of charge carriers. We have used optical-deep level transient to study the valence band offset and the defect states in 10 stacked-Ge quantum dots. From optical DLTS for the QD samples, the peaks related to the valance band offset can be classified distinctly, and especially the peak for the band offset is about 20 - 50 times higher than that for the defect in intensity. The charges emitted from a ground state in the QD confined state are observed near 93 K, and the activation energy is calculated to be E _v+177 meV. The charge state of VBO follows the logarithmic capture kinetics as the optical filling pulses, the apparent activation energy decreases as the optical injection width increases.