No abstract

We report on the generation of triggered single photons obtained from epitaxially grown self-assembled CdSe/Zn(S,Se) quantum dots for temperatures up to 200 K. At low temperatures (T<40 K) photon correlation experiments under pulsed excitation show nearly perfect single-photon emission from an individual CdSe quantum dot. For higher temperatures (T>40 K) an increasing multi-photon emission probability due to spectrally overlapping acoustic phonon sidebands of neighboring quantum dots is observed. We found that the multi-photon emission probability of a bare quantum dot (background subtracted) is strongly suppressed at 200 K if compared to a Poissonian light source of the same average intensity. Our results demonstrate the large potential of self-assembled CdSe/Zn(S,Se) quantum dots for nonclassical light generation at temperatures up to 200 K.

The quantum-confined Stark effect in a single self-assembled CdSe/ZnSe quantum dot was studied by means of highly spatially resolved photoluminescence spectroscopy. A nanotechnological approach making use of a capacitor-like geometry enabled us to apply a well-defined lateral electric field on the quantum dots. Stark shifts of up to 1.1 meV were obtained, which can be well fitted by a purely quadratic dependence on an electric field. In quite good agreement with theoretical calculations, an exciton polarizability of 4.9×10−3 meV/(kV/cm)2 can be extracted, while the permanent dipole moment in the lateral direction is found to be negligible.

Thin AlO x films were grown on 4H-SiC by plasma-assisted atomic layer deposition (ALD) and plasma assisted electron-beam evaporation at 300˚C. After deposition, the films were annealed in nitrogen at temperatures between 500˚C and 1050˚C. The films were analyzed by X-ray reflectivity (XRR) and atomic force microscopy (AFM) in order to determine film thickness, surface roughness and density of the AlO x layer. No differences were found in the behavior of AlO x films upon annealing for the two different employed deposition techniques. Annealing results in film densification, which is most prominent above the crystallization temperature (800˚C). In addition to the increasing density, a mass loss of ~5% was determined and attributed to the presence of aluminum oxyhydroxide in as deposited films. All changes in film properties after high temperature annealing appear to be independent of the deposition technique.

There is a high demand for compact low-cost ozone sensors. It has been shown recently that In2O3 nanolayers can act as ozone sensitive films activated at room temperature by ultraviolet light. In the present work, the authors integrate ultrathin layers of In2O3 nanoparticles and a GaInN∕GaN based blue light emitting diode (LED) on a single sensor chip. The integrated sensor was found to be sensitive to O3 concentrations as low as ∼40ppb. These results demonstrate that by integrating GaInN∕GaN based blue LEDs and metal oxide sensing layers back to back on a single chip, compact and robust gas sensors can be realized.