Hole emission processes in InAs/GaAs self-assembled quantum dots

We present a study of the hole emission processes in InAs/GaAs quantum dots using capacitance and admittance spectroscopies. From the conductance mapping, the hole levels show a quasicontinuous distribution, instead of the clear shell structures that have been observed in electron systems. According to a comparative analysis of the capacitance and admittance spectroscopies, the hole emission process is identified to be via thermally activated tunneling through the wetting layer as an intermediate state. An energy level diagram of the quantum dot is also constructed, which shows the hole in our quantum dots to be more weakly confined. We propose a general thermally activated tunneling model to explain our results and those in other works. The conclusion is that both the localization energy and the electric field are important for the carrier emission processes. This model is further extended to predict which carrier type (i.e., electron or hole) will be more relevant during the exciton dissociation processes in quantum dots.