Excitation-dependent Polarized Emission from GaN/AlN Quantum Dot Ensembles under In-plane Uniaxial Stresses

The effects of uniaxial stress and variable excitation on the optical properties of GaN/AlN quantum dots (QDs) grown on Si(111) substrates have been investigated. We show that post-growth microcracks which are created during cooling of the sample serve as excellent stressors through which the strain tensor of the QDs can be modified for studies of strain-induced changes in the optical properties. We have used cathodoluminescence (CL) imaging and spectroscopy with polarization detection to probe limited regions of the sample in which the QDs are subject to in-plane uniaxial stresses of 20 to 30 kbar. CL measurements of the QD excitonic transitions exhibit an in-plane linear polarization anisotropy in close proximity to microcracks that is strongly dependent on the e-beam current used to excite the QD ensemble. Theoretical modeling was performed, as based on self-consistent solutions of the Schrodinger and Poisson equations using the 6x6 k.p and effective mass methods for the calculation of the QD hole and electron states.