Optical properties of photonic molecules and elliptical pillars made of ZnSe-based microcavities.

The influence of the geometric shape of optically confining structures on the emission properties of ZnSe-based microcavities is studied. Elliptical as well as coupled circular structures were fabricated with quantum wells or quantum dots as optical active material. For the elliptical pillars a lifting of the polarization degeneracy of the resonator modes is observed as it is favorable to control the polarization state of the emitted photons. The influence of the ellipticity on the polarization splitting of the fundamental mode as well as on the quality factor of the sample is discussed. For the coupled pillar microcavities the effect of their distance on the energy splitting of the fundamental resonator mode is analyzed. Furthermore, detailed measurements of the spatial mode distribution in elliptically shaped pillars and photonic molecules are performed. By comparing these results to the calculated mode distribution their analogy to a diatomic molecule is illustrated. It turns out that the observed mode splitting into localized bonding and delocalized antibonding states in ZnSe-based microcavities is more pronounced for elliptical geometries. The realization of delocalized mode profiles is favorable for the coupling of spatially separated quantum dots.

Light-emitting diode based on mask- and catalyst-free grown N-polar GaN nanorods.

We report on the fabrication of a light-emitting diode based on GaN nanorods containing InGaN quantum wells. The unique system consists of tilted N-polar nanorods of high crystalline quality. Photoluminescence, electroluminescence, and spatially resolved cathodoluminescence investigations consistently show quantum well emission around 2.6 eV. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy measurements reveal a truncated shape of the quantum wells with In contents of (15 ± 5)%.

Electroluminescence from a single InGaN quantum dot in the green spectral region up to 150 K.

We present electrically driven luminescence from single InGaN quantum dots embedded into a light emitting diode structure grown by metal-organic vapor-phase epitaxy. Single sharp emission lines in the green spectral region can be identified. Temperature dependent measurements demonstrate thermal stability of the emission of a single quantum dot up to 150 K. These results are an important step towards applications like electrically driven single-photon emitters, which are a basis for applications incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.

A CdSe quantum dot based resonant cavity light-emitting diode showing single line emission up to 90 K.

A II-VI wide-bandgap resonant cavity light-emitting diode is presented. The active region consists of CdSe quantum dots embedded in ZnSSe/MgS barriers, resulting in improved quantum efficiency at elevated temperatures. The resonant cavity is formed by a 14-period bottom distributed Bragg reflector and the semiconductor to air interface on top of the structure. Temperature dependent micro-electroluminescence measurements reveal emission of a single quantum dot up to 90 K. The turn-on voltages are 6 V at 4 K and 4 V at room temperature. These results are promising for the realization of green surface-emitting devices in general, and especially for an electrically driven prospective single photon source operating at room temperature.

Highly ordered catalyst-free and mask-free GaN nanorods on r-plane sapphire.

Self-organized and highly ordered GaN nanorods were grown without catalyst on r-plane sapphire using a combination of molecular beam epitaxy and metal-organic vapor-phase epitaxy. AlN nucleation centers for the nanorods were prepared by nitridation of the sapphire in a metal-organic vapor-phase epitaxy reactor, while the nanorods were grown by molecular beam epitaxy. A coalesced two-dimensional GaN layer was observed between the nanorods. The nanorods are inclined by 62 degrees towards the [Formula: see text]-directions of the a-plane GaN layer. The high degree of ordering and the structural perfection were confirmed by micro-photoluminescence measurements.