Quantum dot molecules: A potential pathway towards terahertz devices

A study of structural and optical properties of In0.3Ga0.7As/GaAs quantum dot molecules (QDMs) formed by two layers of self-assembled, vertically stacked quantum dots (QDs) is presented in this paper. Structural parameters such as the dot shape and size, as determined from high-resolution transmission electron microscopy (HRTEM) studies were used to calculate the strain in samples with vertically isolated, quantum decoupled dots (QDD) and in samples with vertically ordered, coupled pairs of dots forming QDMs. The calculated strain field was subsequently used to determine the electronic bandstructure of the QDD and QDM samples, in the framework of the eight-band k·p perturbation theory. The theoretically calculated electronic bandstructures were found to be in good agreement with those experimentally measured by using the time integrated photoluminescence (PL) technique. In order to understand the QDM properties, which could potentially be used for designing new emission devices, excitation and temperature dependence studies of the PL in both QDD and QDM structures were conducted. A qualitative explanation of the temperature dependence of the full-width at half-maximum (FWHM) is also provided. Optical and electronic properties of QDMs are compared with those of QDDs grown under similar conditions.