A. Gust

Room temperature emission from CdSe∕ZnSSe∕MgS single quantum dots

The authors report on room temperature photoluminescence from single CdSe quantum dots. The quantum dots, realized by self-organized epitaxial growth, are embedded in ZnSSe∕MgS barriers. The integrated intensity of the emission drops by less than a factor of 3 between 4K and room temperature. Microphotoluminescence with a spatial resolution of 200nm exhibits single dot emission that remains visible up to 300K. The linewidth of the single dot emission increases thereby from 340μeVto25meV at room temperature, which the authors attribute to the interaction of excitons with optical phonons.

Electrically driven single quantum dot emitter operating at room temperature

We present both optically and electrically driven room temperature emission from single CdSe quantum dots, realized by self-organized epitaxial growth. A structure design that embeds the CdSe quantum dots into ZnSSe/MgS barriers results in high carrier confinement and exceptionally large quantum efficiencies at room temperature. Microphotoluminescence with a spatial resolution of 200 nm exhibits single dot emission that remains visible up to 300 K. When integrating these quantum dots into p-i-n diode structures, an electrically driven single dot emitter with pronounced room temperature emission is realized. The linewidth of the single dot emission increases with temperature due to exciton-phonon interaction and reaches 26 meV at 300 K. This value is only slightly larger than the biexcitonic binding energy, opening a way to solid state single photon emitters operating at elevated temperatures.

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.

In situ observation of Zn-induced etching during CdSe quantum dot formation using time-resolved ellipsometry

A combined segregation and desorption process has been observed in situ by ellipsometry in real-time during overgrowth of a CdSe layer by a ZnSe cap layer using migration enhanced epitaxy. This segregation enhanced etching of CdSe during Zn deposition is known to play an important role in the formation process of CdSe quantum dots. The time-resolved ellipsometry data can be fitted assuming a rapid thickness reduction of about 68% of the CdSe layer, consistent with results obtained by high-resolution x-ray diffraction after growth. Furthermore, a significant change in growth rate during deposition of CdSe has been observed.

Coherent propagation of polaritons in semiconductor heterostructures : Nonlinear pulse transmission in theory and experiment

The influence of coherent optical nonlinearities on polariton effects is studied by means of a detailed comparison of theory and experiment. A unique approach that combines a microscopic treatment of the boundary problem in a sample of finite thickness with excitonic and biexcitonic nonlinearities is introduced. Spectral changes that depend on the light polarization are analyzed for single pulse transmission and pump and probe excitation.

Electrically driven room temperature operation of a single quantum dot emitter

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.

Bragg polaritons in a ZnSe-based unfolded microcavity at elevated temperatures

In this contribution, we present strong coupling of ZnSe quantum well excitons to Bragg modes resulting in the formation of Bragg polariton eigenstates, characterized by a small effective mass in comparison to a conventional microcavity. We observe an anticrossing of the excitonic and the photonic component in our sample being a clear signature for the strong-coupling regime. The anticrossing is investigated by changing the detuning between the excitonic components and the Bragg mode. We find anticrossings between the first Bragg mode and the heavy- as well as light-hole exciton, respectively, resulting in three polariton branches. The observed Bragg-polariton branches are in good agreement with theoretical calculations. The strong indication for the existence of strong coupling is traceable up to a temperature of 200 K, with a Rabi-splitting energy of 24 meV and 13 meV for the Bragg mode with the heavy- and light-hole exciton, respectively. These findings demonstrate the advantages of this sample configu...

Electrically driven single photon emission from a CdSe/ZnSSe single quantum dot at 200 K

High temperature operation of an electrically driven single photon emitter based on a single epitaxial quantum dot is reported. CdSe/ZnSSe/MgS quantum dots are embedded into a p-i-n diode architecture providing almost background free excitonic and biexcitonic electroluminescence from individual quantum dots through apertures in the top contacts. Clear antibunching with g2(τ = 0) = 0.28 ± 0.20 can be tracked up to T = 200 K, representing the highest temperature for electrically triggered single photon emission from a single quantum dot device.

Polarized light emission from CdSe/ZnSSe quantum-dot monolithic pillar microcavities

Small-size II-VI micropillars with asymmetrical cross sections are presented as a way to achieve more than 95% of the emitted light from single quantum dots having one particular linear polarization state. We show that the detected PL intensity of the QD is increased by optimizing the spectral overlap between QD emission and resonator mode. The polarization of the emitted light is defined by the polarization of the resonator mode. Moreover, the internal mode structure in photonic molecules is investigated by studying their far field pattern. The observed field distribution opens the possibility of coupling individual quantum dots to each other via the mediation of the electromagnetic field.

Wide-Bandgap Quantum Dot Based Microcavity VCSEL Structures

In this contribution we report on the optical properties of planar and pillar structured GaN- and ZnSe-based monolithic microcavities. These structures reveal three-dimensional confined optical modes with high quality factors and potentially small mode volumes especially for the ZnSe-based samples. The measurements are completed with theoretical calculations. Furthermore, the optical emission properties of CdSe quantum dots embedded into microcavities have been studied. The Purcell effect demonstrated by means of the pronounced enhancement of the spontaneous emission rate of quantum dots coupled to the discrete optical modes of the cavities. This enhancement depends systematically on the pillar diameter and thus on the Purcell factor of the individual pillars.