We present an electrically driven single quantum dot emitter that is adapted for operation at room temperature. Epitaxially grown CdSe quantum dots were embedded between ZnSSe/MgS barriers optimized with respect to both, high quantum efficiency and efficient current injection at elevated temperatures. Most important, electroluminescence from one single quantum dot is observed even at room temperature with a surprisingly low driving voltage of 2.6 V. This might be a key step for a single photon emitter operating under ambient conditions.
Semiconductor nanoparticles are attractive candidates for future large-area light emitting devices that are both costeffective
and robust. We demonstrate a ZnO nanoparticle light emitting device realised without organic support layers.
Tight layers with subμm thickness were fabricated using commercially available ZnO nanoparticles from the gas phase
and fluorine-doped tin oxide glass as a substrate. After evaporation of a top electrode, a non-linear I-V characteristic was
obtained. At room temperature, the device operates at voltages of only few Volts and shows electroluminescence in the
visible spectral range and a pronounced UV peak related to near-band emission of the ZnO.
Single epitaxially grown CdSe/ZnSe quantum dots have been studied by using photoluminescence spectroscopy with a high spatial resolution. The lifting of the spin degeneracy due to exchange interaction results in a splitting of the exciton ground state, strongly dependent on the symmetry of the quantum dot. By applying a magnetic field in Faraday geometry, the energy splitting as well as the polarization properties of the exciton transition can be varied and remarkably, even at high magnetic field a spin coherence time of about 3 ns is found, which exceeds the recombination lifetime of single excitons significantly. As the biexciton state is a spin singlet, both its fine structure splitting as well as its degree of polarization are shown to be controlled by the final state of recombination, the single exciton state. Besides the discrete energy splitting of optical transitons in single quantum dots, we observe a rather statistical, but strongly correlated energy shift was well as a correlated on-off switching behavior of the exciton and the biexciton emission on a typical time constant of seconds. These effects are related to the influence of charge carriers in the nanoenvironment of the dot and to thermal or Auger-driven carrier escape into trap states in the vicinity of the dot, respectively.