Timeand energy-resolved photoluminescence (PL) measurements on InGaN/GaN quantum dots (QDs) are presented. Although the PL decay is strongly non-exponential for all detection energies, excitation density dependent measurements yield no indication for dynamical screening effects. We show that the non-exponential decay is well explained with a broad distribution of excitonic lifetimes within the QD ensemble. Using an inverse Laplace transformation, we derive an energy-dependent lifetime distribution function, which is in very good agreement with recently published single-QD time-resolved PL measurements. Within the framework of eight-band k·p theory, we calculate the dependence of the radiative excitonic lifetimes on structural parameters, like QD height, lateral diameter, and chemical composition. The built-in piezoand pyroelectric fields cause a sensitive dependence of the radiative lifetimes on the exact QD geometry and composition, resulting in a broad lifetime distribution even for moderate variations of the QD structure.

Molecular beam epitaxy-grown GaN with different Mn concentrations (5-23 x 10 cm) and codoped with Si were investigated by cathodoluminescence (CL) spectroscopy and optical transmission measurements. In the GaN:Mn, an intense absorption peak at 1.414 +/0.002 eV was observed. This peak was attributed to an internal T2 E transition of the deep neutral Mn state since its intensity scaled with the Mn concentration. The CL measurements showed that Mn-doping concentrations around 10 cm had three effects on the emission spectrum: (i) the donor bound exciton at 3.460 eV was reduced by more than one order of magnitude, (ii) the donor-acceptor-pair band at 3.27 eV was completely quenched and (iii) the yellow luminescence centered at 2.2 eV was the strongly decreased. The latter two effects were attributed to a reduced concentration of VGa. In the infrared spectral range, three broad, Mn-doping related CL emission bands centered at 1.01 ± 0.02 eV, 1.09 ± 0.02 eV and 1.25 ± 0.03 eV were observed. These bands might be related to deep donor complexes, which are generated as a result of the heavy Mn-doping, rather than internal transitions at the Mn atom.

We studied gain and absorption in CdSe quantum dots (QDs) in a ZnSe matrix. It was demonstrated that, caused by a strong excitonic absorption, excitonic waveguiding occurs in edge geometry. No significant change of the gain maximum energy over a range of two magnitudes above the threshold was detected. Magneto-optical investigations demonstrate the strong lateral localisation of excitons at CdSe QDs in agreement with lack of exciton screening in QDs revealed in gain studies.

The phenomenon of light confinement in an isolated quantum dot, originating from the electromagnetic wave diffraction at the dot boundary, is discussed. It has been shown that at a certain condition the quantum dot behaves as a microcavity whose eigenmodes manifest themselves as additional, geometrical, resonances in the quantum dot electromagnetic response. The effect of induced magnetization of the quantum dot is predicted and illustrated by the example of magnetic resonances in spherical quantum dots. The radiative lifetime for a spherical quantum dot has been evaluated and a correlation has been discussed between radiative lifetimes in quantum dots and quantum wells.

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