Electronic structure and optical behavior of self-assembled InAs quantum dots

Abstract

Using both electrical and optical techniques, ground state energy levels and excited states of carriers in self-assembled InAs quantum dots are described, and the first observations of mid-infrared photoconductivity in these structures are presented. Electrical measurements including ac conductance and Hall techniques have been used to determine thermal trapping of carriers, and yield strong binding for holes, less binding for electrons, and an exciton energy that is consistent with photoluminescence (PL) measurements. Further PL experiments have probed the effect of changing the InAs dot size, and using embedding material of different composition. Several of these structures also demonstrate strong electron binding. In devices where the InAs dots have been grown in an Al0.3Ga0.7As matrix and surrounded by AlAs barriers, normal incidence photoconductivity has been observed at a range of wavelengths in the mid-infrared and attributed to single carrier transitions out of the dots. This mid-infrared optical response is investigated for several different dot structures and compared to photoluminescence data from the same samples.