Yuriy I. Mazur

Intersublevel Infrared Photodetector with Strain-Free GaAs Quantum Dot Pairs Grown by High-Temperature Droplet Epitaxy

Normal incident photodetection at mid infrared spectral region is achieved using the intersublevel transitions from strain-free GaAs quantum dot pairs in Al(0.3)Ga(0.7)As matrix. The GaAs quantum dot pairs are fabricated by high temperature droplet epitaxy, through which zero strain quantum dot pairs are obtained from lattice matched materials. Photoluminescence, photoluminescence excitation optical spectroscopy, and visible-near-infrared photoconductivity measurement are carried out to study the electronic structure of the photodetector. Due to the intersublevel transitions from GaAs quantum dot pairs, a broadband photoresponse spectrum is observed from 3 to 8 microm with a full width at half-maximum of approximately 2.0 microm.

1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on Si substrates using InAlAs/GaAs dislocation filter layers

We report on the operation of electrically pumped 1.3μm InAs QD laser directly grown on a Si substrate using InAlAs/GaAs dislocation filter layers with a threshold current density of 194A/cm2 and output power of ~80mW.

Self-organization of quantum-dot pairs by high-temperature droplet epitaxy

The spontaneously formation of epitaxial GaAs quantum-dot pairs was demonstrated on an AlGaAs surface using Ga droplets as a Ga nano-source. The dot pair formation was attributed to the anisotropy of surface diffusion during high-temperature droplet epitaxy.

Strain-free ring-shaped nanostructures by droplet epitaxy for photovoltaic application

Droplet epitaxy is a flexible nanomaterial growth technique and is a potential method to fabricate advanced electronic and optoelectronic devices. Here, we report strain-free GaAs/Al0.33Ga0.67As quantum ring solar cells fabricated by droplet epitaxy technique. Photoluminescence is used to study the electronic structure of the lattice-matched GaAs/Al0.33Ga0.67As quantum ring solar cells. Post-growth thermal annealing is used to improve the optical quality of the solar cell as well as device efficiency. A power conversion efficiency of 1.8% is demonstrated from a prototype quantum ring solar cell. This work opens new opportunities for quantum dot solar cells with strain-free nanostructures.

Laterally aligned quantum rings: From one-dimensional chains to two-dimensional arrays

We present the fabrication of ordered quantum rings by the conversion of partially capped quantum dots. Morphological transformation of quantum dots to quantum rings is demonstrated by partially capping self-assembled quantum dots. Quantum rings have been fabricated on high index surfaces by this growth technique. The lateral ordering of quantum rings is introduced by engineering the strain field of a multi-layer InGaAs superlattice template. By using high index surfaces, the one-dimensional ordering of quantum rings on GaAs (100) surface was observed to evolve into two-dimensional aligned quantum ring arrays.

Energy Transfer within Ultralow Density Twin InAs Quantum Dots Grown by Droplet Epitaxy

Ultralow density (approximately 10(6)/cm(2)) of twin InAs quantum dot (QD) hybrid structure was grown by a droplet epitaxy technique. The photoluminescence (PL) from ensemble and individual twin InAs QD structures showed a bimodal behavior and an energy transfer between the well-separated (approximately 190 nm) twin QDs, which was supposedly due to the special wetting ring that built the channel for exciton transfer. This research demonstrates a novel approach to fabricate lateral InAs QD pairs as the candidate for a laterally coupled QD molecule.

Substrate effects on the strain relaxation in GaN/AlN short-period superlattices

We present a comparative study of the strain relaxation of GaN/AlN short-period superlattices (SLs) grown on two different III-nitride substrates introducing different amounts of compensating strain into the films. We grow by plasma-assisted molecular beam epitaxy (0001)-oriented SLs on a GaN buffer deposited on GaN(thick)-on-sapphire template and on AlN(thin)-on-sapphire template. The ex-situ analysis of strain, crack formation, dislocation density, and microstructure of the SL layers has established that the mechanism of strain relaxation in these structures depends on the residual strain in substrate and is determined mainly by the lattice mismatch between layers. For growth on the AlN film, the compensating strain introduced by this film on the layer prevented cracking; however, the densities of surface pits and dislocations were increased as compared with growth on the GaN template. Three-dimensional growth of the GaN cap layer in samples with pseudomorphly grown SLs on the AlN template is observed. At the same time, two-dimensional step-flow growth of the cap layer was observed for structures with non-pseudomorphly grown SLs on the GaN template with a significant density of large cracks appearing on the surface. The growth mode of the GaN cap layer is predefined by relaxation degree of top SL layers.

Photoluminescence linewidths from multiple layers of laterally self-ordered InGaAs quantum dots

Laterally ordered multilayered arrays of InGaAs quantum dots are investigated by photoluminescence as a function of high index GaAs substrates. Different laser wavelengths are used to investigate the photoluminescence from quantum dots layer-by-layer. High optical quality is demonstrated for laterally ordered quantum dot arrays. GaAs(511)B is identified as the optimum high index substrate for growth of InGaAs∕GaAs multilayered quantum dots, demonstrating strong photoluminescence with a narrow full width at half maximum linewidth of 23meV in spite of the potential for misfit dislocations.

Molecular beam epitaxy growth of GaAsBi/GaAs/AlGaAs separate confinement heterostructures

GaAsBi/GaAs/AlGaAs separate confinement heterostructures are grown using an asymmetric temperature profile due to the low optimal growth temperature of GaAsBi; the bottom AlGaAs barrier is grown at 610 °C, while the GaAsBi quantum well and the top AlGaAs barrier are grown at 320 °C. Cross-sectional transmission electron microscopy and room temperature photoluminescence measurements indicate that this approach results in samples with excellent structural and optical properties. The high quality of the low temperature AlGaAs barrier is attributed to the presence of Bi on the surface as indicated by a (1 × 3) surface reconstruction persisting throughout the low temperature growth.

Bi-stability, hysteresis, and memory of voltage-gated lysenin channels.

Lysenin, a 297 amino acid pore-forming protein extracted from the coelomic fluid of the earthworm E. foetida, inserts constitutively open large conductance channels in natural and artificial lipid membranes containing sphingomyelin. The inserted channels show voltage regulation and slowly close at positive applied voltages. We report on the consequences of slow voltage-induced gating of lysenin channels inserted into a planar Bilayer Lipid Membrane (BLM), and demonstrate that these pore-forming proteins constitute memory elements that manifest gating bi-stability in response to variable external voltages. The hysteresis in macroscopic currents dynamically changes when the time scale of the voltage variation is smaller or comparable to the characteristic conformational equilibration time, and unexpectedly persists for extremely slow-changing external voltage stimuli. The assay performed on a single lysenin channel reveals that hysteresis is a fundamental feature of the individual channel unit and an intrinsic component of the gating mechanism. The investigation conducted at different temperatures reveals a thermally stable reopening process, suggesting that major changes in the energy landscape and kinetics diagram accompany the conformational transitions of the channels. Our work offers new insights on the dynamics of pore-forming proteins and provides an understanding of how channel proteins may form an immediate record of the molecular history which then determines their future response to various stimuli. Such new functionalities may uncover a link between molecular events and macroscopic processing and transmission of information in cells, and may lead to applications such as high density biologically-compatible memories and learning networks.