Different paths to tunability in III–V quantum dots

Abstract

Tunability in the concentration and average dimensions of self-forming semiconductor quantum dots (QDs) has been attained. Three of the approaches examined here are: variations with temperature, group V partial pressure and with substrate miscut angle. Thermally activated group III adatom mobilities result in larger diameters and lower concentrations with increasing deposition temperatures. These variations are presented for InGaAs/GaAs and AlInAs/AlGaAs, where striking differences were seen. Tunability in the InGaAs/GaAs QD concentration was also obtained in metalorganic chemical vapor deposition by varying the arsine flow. The latter gave widely varying concentrations and similar sizes. Substrate orientation was found to also be a key factor in island nucleation: Changes in vicinal orientation near (100) can be used to exploit the preferential step edge nucleation at mono and multi-atomic steps, so varying miscut angle (θm) can be used to change island densities and sizes. Anisotropies in island nucleation producing n-dot strings aligned with multiatomic step edges are observed for θm⩾0.75° and up to 2°. Quantum mechanical coupling from such island strings result in non-Gaussian shapes in the inhomogeneously broadened photoluminescence peaks. The effects of some of the other morphological differences presented here on the luminescence emission from QD ground states is discussed for InGaAs/GaAs QDs.