Demonstration of a GaSb/GaAs Quantum Dot Intermediate Band Solar Cell Operating at Maximum Power Point.

Intermediate band solar cells (IBSCs) promise high efficiencies while maintaining a low device structural complexity. A high efficiency can be obtained by harvesting below-band-gap photons, thus increasing the current, while at the same time preserving a high voltage. Here, we provide experimental proof that below-band-gap photons can be used to produce nonzero electrical work in an IBSC without compromising the voltage.

Structural and optical properties of disc-in-wire InGaN/GaN LEDs.

This study examines the role of the microstructure and optical properties of InGaN/GaN nanowire LED structures on Si(111) having different nanowire coverages. Cathodoluminescence (CL) measurements show that all samples exhibit broad emission around the intended energy, 1.95 eV (635 nm).

Ordered arrays of embedded Ga nanoparticles on patterned silicon substrates.

We fabricate site-controlled, ordered arrays of embedded Ga nanoparticles on Si, using a combination of substrate patterning and molecular-beam epitaxial growth. The fabrication process consists of two steps. Ga droplets are initially nucleated in an ordered array of inverted pyramidal pits, and then partially crystallized by exposure to an As flux, which promotes the formation of a GaAs shell that seals the Ga nanoparticle within two semiconductor layers.

Time-resolved two-pulse excitation of quantum dots coupled to a photonic crystal cavity in the Purcell regime.

We investigate the nonlinear emission dynamics of quantum dots coupled to photonic crystal cavities in the Purcell regime using luminescence intensity autocorrelation. Two laser pulses with a controlled time delay sequentially excite the coupled system inducing emission that depends on the delay and laser power. We find distinct contrasts between exciton and biexciton emission as a function of time delay which originate from different nonlinearities.

Electrical transport in ion beam created InAs nanospikes.

Ion beam irradiation has previously been demonstrated as a method for creating nanowire-like semiconductor nanostructures, but no previous studies have reported on the electrical properties of those structures. In this work we describe the creation and in situ transmission electron microscopy electrical characterization of nanoscale InAs spike structures on both InAs and InP substrates fabricated using a focused ion beam erosion method. Those InAs 'nanospikes' are found to possess internal structures with varying amounts of ion damaged and single crystalline material.

Lateral patterning of multilayer InAs/GaAs(001) quantum dot structures by in vacuo focused ion beam.

We report on the effects of patterning and layering on multilayer InAs/GaAs(001) quantum dot structures laterally ordered using an in vacuo focused ion beam. The patterned hole size and lateral pattern spacing affected the quantum dot size and the fidelity of the quantum dots with respect to the lateral patterns. 100% pattern fidelity was retained after six layers of dots for a 9.

Focused ion beam creation and templating of InAs and InAs/InP nanospikes.

Ion beam irradiation has been examined as a method for creating nanoscale semiconductor pillar and cone structures, but has the drawback of inaccurate nanostructure placement. We report on a method for creating and templating nanoscale InAs spikes by focused ion beam (FIB) irradiation of both homoepitaxial InAs films and heteroepitaxial InAs on InP substrates. These 'nanospikes' are created as In droplets, formed due to FIB irradiation, act as etch masks for the underlying InAs.

Photoluminescence imaging of focused ion beam induced individual quantum dots.

We report on scanning microphotoluminescence measurements that spectrally and spatially resolve emission from individual InAs quantum dots that were induced by focused ion beam patterning. Multilayers of quantum dots were spaced 2 μm apart, with a minimum single dot emission line width of 160 μeV, indicating good optical quality for dots patterned using this technique. Mapping 16 array sites, at least 65% were occupied by optically active dots and the spectral inhomogeneity was within 30 meV.

Toward Assembly of Non-close-packed Colloidal Structures from Anisotropic Pentamer Particles.

Particles combining multiple anisotropy dimensions offer possibilities for self-assembly that have not been extensively explored to date. The scope for assembly of microparticles in which the anisotropy dimensions of internal bond angle and chemical ordering have been varied is investigated. Colloidal assemblies with interesting open (i.

Filling of hole arrays with InAs quantum dots.

Focused ion beams are used to pattern GaAs(001) surfaces with an array of nanometer-deep holes upon which deposition of InAs results in quantum dot formation at the hole location. Experiments show that the size and quantity of quantum dots formed depend on growth parameters, and ion dose, which affects the size and shape of the resulting holes. Quantum dots fabricated in this fashion have a photoluminescence peak at 1.

Fluidic assembly and packing of microspheres in confined channels.

We study fluidic assembly and packing of spherical particles in rectilinear microchannels that are terminated by a flow constriction. First, we introduce a method for active assembly of particles in the confined microchannels by triggering a local constriction in the fluid channel using a partially closed membrane valve. This microfluidic valve allows active, on-demand particle assembly as opposed to previous passive assembly methods based on terminal channels and weirs.

Programmable fluidic production of microparticles with configurable anisotropy.

We report a technique for continuous production of microparticles of variable size with new forms of anisotropy including alternating bond angles, configurable patchiness, and uniform roughness. The sequence and shape of the anisotropic particles are configured by exploiting a combination of confinement effects and microfluidics to pack precursor colloids with different properties into a narrow, terminal channel. The width and length of the channel relative to the particle size fully specify the configuration of the anisotropic particle that will be produced.