Effects of growth interruption on self-assembled InAs/GaAs islands

The effect of growth interruption on the InAs deposition and its subsequent growth as self-assembled island structures, in particular the material transport process of the InAs layers has been investigated by photoluminescence and transmission electron microscopy measurements. InAs material in structures with only coherent islands transfers from the wetting layer to the formed islands and the growth interruption causes a red shift of PL peak energy. On the other hand, the PL peak shifts to higher energy in structures containing simultaneously coherent and noncoherent islands with dislocations. In this case, the noncoherent islands capture InAs material from the surrounding wetting layer as well as coherent islands, which casues a reduction in the size of these islands. The variations in the PL intensity and line width are also discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

Growth and transport properties of InAs thin films on GaAs

High-quality InAs epitaxial layers have been grown on (1 0 0) oriented semi-insulating GaAs substrates by MBE. The transport properties of largely lattice mismatched InAs/GaAs heterojunctions have been investigated by Hall effect measurements down to 10 K. In spite of a high dislocation density at the heterointerface, very high electron mobilities are obtained in the InAs thin films. By doping Si into the layer far from the InAs/GaAs interface, we found that the doped samples have higher electron mobility than that of the undoped samples with the same thickness. The mobility demonstrates a pronounced minimum around 300 K for the undoped sample. But for Si-doped samples, no pronounced minimum has been found. Such abnormal behaviours are explained by the parallel conduction from the quasi-bulk carriers and interface carriers. These high-mobility InAs thin films are found to be suitable materials for making Hall elements. (C) 1998 Elsevier Science B.V. All rights reserved.

Growth of ZnO single crystal by chemical vapor transport method

ZnO crystals were grown by CVT method in closed quartz tube under seeded condition. Carbon was used as a transport agent to enhance the chemical transport of ZnO in the growth process. ZnO single crystals were grown by using GaN/sapphire and GaN/Si wafer as seeds. The property and crystal quality of the ZnO single crystals was studied by photoluminescence spectroscopy and X-ray diffraction technique.

A novel photonic crystal vertical cavity surface emitting laser based on coherent coupling

We demonstrate a novel oxide confined GaAs-based photonic crystal vertical cavity surface emitting laser (PC-VCSEL) operating at a wavelength of 850 nm based on coherent coupling. A ring-shaped light-emitting aperture is added to the conventional PC-VCSEL, and coherent coupling is achieved between the central defect aperture and the ring-shaped light-emitting aperture. Measurements show that under the continuous-wave (CW) injected current of 20 mA, a high power of 2 mW is obtained, and the side mode suppression ratio (SMSR) is larger than 20 dB. The average divergence angle is 4.2 degrees at the current level of 20 mA. Compared with the results ever reported, the divergence angle is reduced.

Short range scattering mechanism of type-II GaSb/GaAs quantum dots on the transport properties of two-dimensional electron gas

We have studied the scattering process of AlGaAs/GaAs two-dimensional electron gas with the nearby embedded GaSb/GaAs type-II quantum dots (QDs) at low temperature. Quantum Hall effect and Shubnikov-de Haas oscillation were performed to measure the electron density n(2D), the transport lifetime tau(t) and the quantum lifetime tau(q) under various biased gate voltage. By comparing measured results of QDs sample with that of reference sample without embedded QDs, mobilities (transport mobility mu(t) and quantum mobility mu(q)) dominated by GaSb QDs scattering were extracted as functions of n(2D). It was found that the ratios of tau(t) to tau(q) were varying within the range of 1-4, implying the scattering mechanism belonging to the sort of short-range interaction. In the framework of Born approximation, a scattering model considering rectangular-shaped potential with constant barrier height was successfully applied to explain the transport experimental data. In addition, an oscillating ratio of tau(t)/tau(q) with the increasing n(2D) was predicted in the model.

Coherent laser control in attosecond sum-frequency polarization beats using twin noisy driving fields

Based on the phase-conjugate polarization interference between two-pathway excitations, we obtained an analytic closed form for the second-order or fourth-order Markovian stochastic correlation of the V three-level sum-frequency polarization beat (SFPB) in attosecond scale. Novel interferometric oscillatory behavior is exposed in terms of radiation-radiation, radiation-matter, and matter-matter polarization beats. The phase-coherent control of the light beams in the SFPB is subtle. When the laser has broadband linewidth, the homodyne detected SFPB signal shows resonant-nonresonant cross correlation, a drastic difference for three Markovian stochastic fields, and the autocorrelation of the SFPB exhibits hybrid radiation-matter detuning terahertz damping oscillation. As an attosecond ultrafast modulation process, it can be extended intrinsically to any sum frequency of energy levels. It has been also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced controllable dispersion effects between the two arms of interferometer do not affect the overall accuracy in case using the SFPB to measure the Doppler-free energy-level sum of two excited states.

Rashba electron's ballistic transport in two-dimensional quantum waveguide

The ballistic transport of Rashba electrons in a straight structure in two-dimensional electron gas is studied. It is found that there is no mixing between the wave functions of spin up and spin down states, and the transfer matrix is independent for the spin in every interface. The influence of the structure and Rashba coefficient on the electron transport is investigated. Our results indicate that the transmission probabilities are independent of the sign and magnitude of the Rashba coefficient and it depends on the shape of the structure, especially the stub width. The antiresonance is found, where the quasiconfined state is formed in the center part of the structure.