Sharp emission from single InAs quantum dots grown on vicinal GaAs surfaces

We report on optical studies of single InAs quantum dots grown on vicinal GaAs(001) surfaces. To ensure low quantum dot density and appropriate size, we deposit InAs layers 1.4 or 1.5 ML thick, thinner than the critical thickness for Stranski–Krastanov quantum dot formation. These dots show sharp and bright photoluminescence. Lifetime measurements reveal an exciton lifetime of 500 ps. Polarization measurements show an exciton fine structure splitting of 15??eV and allow to identify the exciton and charged exciton transitions with linewidth as narrow as 23??eV.Kavli Institute of NanoscienceApplied Science

Tuning single GaAs quantum dots in resonance with a rubidium vapor

We study single GaAs quantum dots with optical transitions that can be brought into resonance with the widely used D2 transitions of rubidium atoms. We achieve resonance by Zeeman or Stark shifting the quantum dot levels. We discuss an energy stabilization scheme based on the absorption of quantum dot photoluminescence in a rubidium vapor. This offers a scalable means to counteract slow spectral diffusion in quantum dots.QN/Quantum NanoscienceApplied Science

Potential of semiconductor nanowires for single photon sources

The catalyst-assisted growth of semiconductor nanowires heterostructures offers a very flexible way to design and fabricate single photon emitters. The nanowires can be positioned by organizing the catalyst prior to growth. Single quantum dots can be formed in the core of single nanowires which can then be easily isolated and addressed to generate single photons. Diameter and height of the dots can be controlled and their emission wavelength can be tuned at the optical telecommunication wavelengths by the material composition. The final morphology of a wire can be shaped by the radial/axial growth ratio, offering the possibility to form single mode optical waveguides with a tapered end for efficient photon collection.Kavli Institute of NanoscienceApplied Science

Crystal Phase Quantum Well Emission with Digital Control

One of the major challenges in the growth of quantum well and quantum dot heterostructures is the realization of atomically sharp interfaces. Nanowires provide a new opportunity to engineer the band structure as they facilitate the controlled switching of the crystal structure between the zinc-blende (ZB) and wurtzite (WZ) phases. Such a crystal phase switching results in the formation of crystal phase quantum wells (CPQWs) and quantum dots (CPQDs). For GaP CPQWs, the inherent electric fields due to the discontinuity of the spontaneous polarization at the WZ/ZB junctions lead to the confinement of both types of charge carriers at the opposite interfaces of the WZ/ZB/WZ structure. This confinement leads to a novel type of transition across a ZB flat plate barrier. Here, we show digital tuning of the visible emission of WZ/ZB/WZ CPQWs in a GaP nanowire by changing the thickness of the ZB barrier. The energy spacing between the sharp emission lines is uniform and is defined by the addition of single ZB monolayers. The controlled growth of identical quantum wells with atomically flat interfaces at predefined positions featuring digitally tunable discrete emission energies may provide a new route to further advance entangled photons in solid state quantum systems.QN/Quantum NanoscienceQN/Quantum TransportQN/Bakkers La

Longitudinal and transverse exciton-spin relaxation in a single InAsP quantum dot embedded inside a standing InP nanowire using photoluminescence spectroscopy

We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. Elongation of the transverse exciton-spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is well explained by the motional narrowing mechanism induced by Gaussian fluctuations of environmental charges in the nanowire. The longitudinal exciton-spin relaxation time is evaluated by the degree of the random polarization of emission originating from exciton states confined in a single-nanowire quantum dot by using Mueller calculus based on Stokes parameters representation. The reduction in the random polarization component with decreasing excitation power is caused by suppression of the exchange interaction of electron and hole due to an optically induced internal electric field by the dipoles at the wurtzite and zinc-blende heterointerfaces in the InP nanowireQN/Quantum NanoscienceApplied Science