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In this study, we analyze the interaction between excitons and longitudinal-optical phonons (LO phonons) in single, wurtzite GaN quantum dots (QDs) by means of micro-photoluminescence (μL) spectroscopy. We report on Stokes-shifted emission lines measured for hundreds of single QDs. A decrease of the Huang-Rhys factor (~0.5-0.01) is observed with increasing QD emission energy that can be modeled in an adiabatic approximation applying two-particle eight-band k ? p wave functions. In order to obtain the QD dimensions and shape needed for these calculations, we conduct a scanning transmission electron microscope (STEM) analysis, not only focusing on the QD dimensions, but also on alloying effects. The QD height is identified as the most detrimental parameter for the exciton-LO-phonon interaction in strongly polar QD systems based on nitrides. Additionally, we extract the LO-phonon energy for a significant number of individual QDs from our μL data set scaling in-between the bulk values for the QD (GaN) and the matrix material (A1N). Such a large variation of the LO-phonon energy cannot be explained by the alloying effects attested by our STEM analysis. Hence, the exciton-LO-phonon interaction resides in a volume that encloses the QD in the growth direction and a fraction of the matrix material depending on the QD height. We approximate this exciton-LO-phonon interaction volume by a sphere with a constant diameter of 2.6 ± 0.2 nm. [ABSTRACT FROM AUTHOR]

We studied bulk crystals of wurtzite AIN by means of uniaxial pressure-dependent Raman measurements. As a result, we derive the phonon pressure coefficients and deformation potentials for all zone center optical phonon modes. For the A1 and E1 modes, we further experimentally determined the uniaxial pressure dependence of their longitudinal optical-transverse optical (LO-TO) splittings. Our experimental approach delivers new insight into the large variance among previously reported phonon deformation potentials, which are predominantly based on heteroepitaxial growth of AIN and the ball-on-ring technique. Additionally, the measured phonon pressure coefficients are compared to their theoretical counterparts obtained by density functional theory implemented in the SIESTA package. Generally, we observe a good agreement between the calculated and measured phonon pressure coefficients but some particular Raman modes exhibit significant discrepancies similar to the case of wurtzite GaN and ZnO, clearly motivating the presented uniaxial pressure-dependent Raman measurements on bulk AIN crystals. [ABSTRACT FROM AUTHOR]