The properties of Si and O donors in wurtzite AlN have been studied by means of hybrid functional calculations, finding that both impurities form DX centres. In the case of Si, the stable DX centre is close in energy to the substitutional donor state and to a second metastable DX centre, thus explaining both the persistent effects and the broad range of activation energies observed experimentally. Ionisation energies have been computed for both Si and O donor states.

We investigate the relationship between the multiexponential photoluminescence ͑PL͒ dynamics of large nanocrystal ͑NC͒ ensembles and the intensity intermittency ͑blinking͒ characteristic of single NCs. A general model is developed and a simple fitting form derived for the analysis of PL decay curves allowing the extraction of both the intrinsic radiative recombination rate and an intensity intermittence parameter. The analysis is applied to the PL of a series of Si-NCs embedded in silicon oxide matrices yielding a good agreement between extracted and theoretical recombination rates. An excellent agreement is furthermore reported between the range of power-law exponents obtained and those previously determined through both single-NC experiments and current blinking mechanism theory. We suggest that a similar approach may well be fruitful in the analysis of time-resolved PL for a large variety of other carrier-confined materials.

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Formation energies and concentrations of the most relevant point defects in n-type wurtzite AlN are obtained by first-principle calculations employing a hybrid functional. We show that the incorporation of Si is favoured over O under N-rich growth conditions, but not under Alrich conditions. The triply negatively charged Al vacancy is found to be the defect with the lowest formation energy in n-type AlN and it is therefore expected to be the main compensating acceptor. Under typical physical vapor-phase transport growth conditions, we predict Si concentrations of up to 10 20 cm −3 and net donor concentrations of about 10 18 cm −3 , in good agreement with available experimental data.

We report the structural properties and spatial ordering of multilayer ZnMgTe quantum dots (QDs) embedded in ZnSe, where sub-monolayer quantities of Mg were introduced periodically during growth in order to reduce the valence band offset of ZnTe QDs. The periodicity, period dispersion, individual layer thickness, and the composition of the multilayer structures were determined by comparing the experimental high resolution x-ray diffraction (HRXRD) spectra to simulated ones for the allowed (004) and quasi-forbidden (002) reflections in combination with transmission electron microscopy (TEM) results. Secondary ion mass spectroscopy (SIMS) profiles confirmed the incorporation of Mg inside the QD layers, and the HRXRD analysis revealed that there is approximately 32% Mg in the ZnMgTe QDs. The presence of Mg contributes to higher scattering intensity of the HRXRD, leading to the observation of higher order superlattice peaks in both the (004) and (002) reflections. The distribution of scattered intensity in the reciprocal space map (RSM) shows that the diffuse scattered intensity is elongated along the q x axis, indicating a vertical correlation of the dots, which is found to be less defined for the sample with larger periodicity. The diffuse scattered intensity is also found to be weakly correlated along the q z direction indicating a weak lateral correlation of the dots. V