Al 1 − x In x N layers with an indium content between x=10.5% and x=24% were grown by metal-organic vapor-phase epitaxy and characterized concerning their optical, structural and morphological properties with regard to the realization of optoelectronic devices. The indium content and the strain of these layers were measured by high resolution x-ray diffraction. Ellipsometric measurements were used to determine the optical constants [refractive index n(λ) and extinction coefficient κ(λ)] in dependence of wavelength and indium content. The values determined for the electronic bandgaps are in good agreement with theoretical predictions and previous publications on this topic but are more focused on AlInN layers which are pseudomorphically grown on GaN. A bowing parameter of b=10.3±0.1 was determined for fully strained layers with an indium content between 13% and 24%. In order to investigate the suitability of these layers for use in distributed Bragg reflectors, the surface morphology is characterized with respect to the indium content. Furthermore, the influence of an annealing step which often is necessary during device growth, was studied. The influence of this annealing step on the roughness was analyzed by atomic force microscopy, while structural features are monitored by high resolution secondary electron microscopy images. Based on these results distributed Bragg reflectors for the green spectral region with up to 40 pairs and a peak reflectivity of 97% have been realized. Transmission electron microscopic analysis of the layer interfaces are in good agreement with the atomic force and secondary electron microscopy images of the single layer surfaces.

We have investigated the optical properties of single InGaN quantum dots (QDs) by means of microphotoluminescence (μPL) spectroscopy. The QDs were grown on sapphire substrate using metal organic vapor phase epitaxy. Sharp and isolated single exciton emission lines in the blue spectral range were observed. The QD luminescence shows a strong degree of linear polarization up to 96% perpendicular to the growth axis (c-axis) with no preferential alignment in the xy plane. Second order autocorrelation measurements were performed under pulsed excitation and single photon emission up to 50 K is demonstrated.

We report on a systematic study concerning the realization of nitride-based distributed Bragg reflectors (DBRs) for optoelectronic applications in the near-UV to visible spectral range. Different material combinations are used in order to find an optimized trade-off concerning peak reflectivity, stop band width, and strain state of the Bragg mirrors. For the high refractive index material GaN is used in all cases, while for the low index material a layer of either AlGaN or AlInN, respectively, or a AlN/(In)GaN short-period superlattice (SL) is employed. The best peak reflectivity of 97% at a wavelength of 495 nm is achieved for a lattice matched Bragg reflector based on the GaN/AlInN material combination.Transmission electron microscopy image of a 30-fold distributed Bragg reflector consisting of AlInN (dark) and GaN (bright) layers.

We report on the realization of a high quality distributed Bragg reflector for the blue-violet spectral range, with both high and low refractive index layers lattice matched to the GaAs substrate. Our structure is grown by molecular beam epitaxy (MBE). The high refractive index layer is made of ZnMgSSe, while the low index material consists of a short period superlattice containing MgS and ZnCdSe. The refractive index step of Δn = 0.43 results in a stop band width of 40 nm and the normalized reflectivity exceeds 99% for 21 Bragg pairs.

The integration of InGaN quantum dots into GaN-based monolithic microcavities grown by metal-organic vapor-phase epitaxy is demonstrated. Microphotoluminescence spectra reveal distinct spectrally sharp emission lines around 2.73 eV, which can be attributed to the emission of single InGaN quantum dots. The samples are structured into airpost pillar microcavities. The longitudinal and transversal mode spectra of these cavities are in good agreement with theoretical calculations based on a vectorial transfer-matrix method. Quality factors up to Q=280 have been achieved.