Electrical characteristics of InAs self-assembled quantum dots embedded in GaAs using admittance spectroscopy

GaAs based structures in which are embedded InAs self-assembled quantum dots are studied using admittance measurements taken over a large frequency spectrum and for several temperatures. The presence of quantum dots is evidenced in the capacitance-voltage characteristics by one, or more, plateau-like structures related to the processes of charging and discharging of the quantum dots. Concurrently, the measured conductance exhibits a peak in a certain bias range that coincides with the plateau-like structure in the capacitance but only for temperatures below 150 K. The conductance dependence on both the temperature and applied bias is attributed to two mechanisms of carrier escape/capture mechanisms from the InAs embedded quantum dots into/out of the hosting GaAs; a thermally activated process for temperatures above 80 K and a perceptibly nonthermal tunneling process for temperatures below 40 K. The conductance data is used to estimate rates and activation energies in association with the electron escape mechanisms from the quantum dots.