H. Dartsch

Single photon emission from InGaN/GaN quantum dots up to 50 K

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.

Optical and structural characterization of AlInN layers for optoelectronic applications

Al1−xInxN 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 respec...

High-reflectivity II-VI-based distributed Bragg reflectors for the blue-violet spectral range

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.

Optical properties of InGaN quantum dots in monolithic pillar microcavities

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.

Optical Properties of InGaN Quantum Dots in Monolithic Pillar Microcavities

InGaN quantum dots were successfully implemented into fully epitaxially grown nitride‐based monolithic microcavities. Measured discrete modes of airpost pillar microcavities prepared out of the planar sample are compared to theoretical simulations based on a vectorial‐transfer matrix method. Quality factors of up to 280 have been achieved and the emission of a single quantum dot was traced up to a temperature of 125 K.

TEM analyses of microstructure and composition of AlxGa1−xN/GaN distributed Bragg reflectors

In this work we analyse the microstructure as well as layer thicknesses and Al concentration of AlxGa1−xN/GaN distributed Bragg reflectors (DBRs) by transmission electron microscopy. To gain a high reflectivity of the DBR, a high refractive index contrast Δn is necessary, i. e. high Al content x. On the other hand, this leads to built-in stress. Due to this, cracks and/or dislocations can form and thus the reflectivity can be reduced. An optimum stress compensation and the adjustment of the wavelength reflected by the DBR needs a precise control of the layer thicknesses and the Al content.