Electrical properties of vertically stacked InGaAs/InGaAsP/InP self-assembled quantum dots

We used capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) methods to investigate dependence of the electrical properties of the vertically stacked InGaAs/InGaAsP/InP quantum dot (QD) system on the vertical distance between the InAs QD layers. The DLTS measurements show that two groups of activation energies, 0.33 similar to 0.37 eV and 0.39 similar to 0.43 eV for low and high temperatures, respectively, appear in QD samples and vary with the thickness of the InGaAaP spacer layer. Also, the activation energy of the 100-nm-thick spacer samples has a lower value than that of the thin-spacer (10 nm) sample. From the bias-dependent DLTS measurements for the 10-nm-spacer sample, the quantum energy states of nearby QDs appear to couple and decouple as the gate bias conditions vary.