Anomalous photogalvanic effect of circularly polarized light incident on the two-dimensional electron gas in AlxGa1-xN/GaN heterostructures at room temperature

Under normal incidence of circularly polarized light at room temperature, a charge current with swirly distribution has been observed in the two-dimensional electron gas in Al0.25Ga0.75N/GaN heterostructures. We believe that this anomalous charge current is produced by a radial spin current via the reciprocal spin Hall effect. It suggests a new way to research the reciprocal spin Hall effect and spin current on the macroscopic scale and at room temperature.

Circular photogalvanic effect at inter-band excitation in InN

The circular photogalvanic effect (CPGE) is observed in InN at inter-band excitation. The function of the CPGE induced current on laser helicity is experimentally demonstrated and illustrated with the microscopic model. A spin-dependent current obtained in InN is one order larger than in the AlGaN/GaN heterostructures at inter-band excitation. The dependence of CPGE current amplitude on light power and incident angle can be well evaluated with phenomenological theory. This sizeable spin-dependent current not only provides an opportunity to realize spin polarized current at room temperature, but also can be utilized as a reliable tool of spin splitting investigation in semiconductors. (c) 2007 Published by Elsevier Ltd.

Intrinsic spin hall effect induced by quantum phase transition in HgCdTe quantum wells

The spin Hall effect can be induced by both extrinsic impurity scattering and intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. By tuning the Cd content, the well width, or the bias electric field across the quantum well, the intrinsic spin Hall effect can be switched on or off and tuned into resonance under experimentally accessible conditions.

Effect of counterpart on the tribological behavior and tribo-induced phase transformation of Si

The tribological behaviors and phase transformation of single crystal silicon against Si3N4, Ruby and steel were investigated in this study. It was found that the strong chemical action between silicon and Fe was the key factor to the tribological behavior of silicon as slid against steel. SEM and Raman spectroscopy indicated that phase transformation of single crystal silicon occurred during the running-in period at low sliding velocity as slid against Si3N4 and Ruby. and gave birth to single or a mixture phase of Si-III, Si-XII and amorphous silicon. The high hardness of counterpart and the absence of chemical action between silicon and counterpart facilitated the phase transformation of single crystal silicon. (C) 2008 Elsevier Ltd. All rights reserved.

Evidence of ultrafast energy exchange-induced soft'mode of phonons and lattice instability: a nanotime effect

With a series of supportive experimental phenomena as induced by ion beam bombardment, energetic beaminduced athermal activation process in Si is demonstrated. This is correlated with phenomena induced by ultrafast energy exchange in condensed matter in general. A critical modelling is presented on the above process and a universal concept: the ultrafast energy exchange-induced soft mode of phonons and the lattice instability in condensed matter are proposed.

Photoluminescence degradation in GaN induced by light enhanced surface oxidation

The exponential degradation of the photoluminescence (PL) intensity at the near-band-gap was observed in heavily doped or low-quality GaN with pristine surface under continuous helium-cadmium laser excitation. In doped GaN samples, the degradation speed increased with doping concentration. The oxidation of the surface with laser irradiation was confirmed by x-ray photoemission spectroscopy measurements. The oxidation process introduced many oxygen impurities and made an increase of the surface energy band bending implied by the shift of Ga 3d binding energy. The reason for PL degradation may lie in that these defect states act as nonradiative centers and/or the increase of the surface barrier height reduces the probability of radiative recombination.

Simulation research of nonlinear behavior induced by the charge-carrier effect in resonant-cavity-enhanced photodetectors

In this paper, we have calculated and discussed in detail the nonlinear effect induced by three carrier effects: free-carrier absorption, bandgap filling, and bandgap shrinkage. The central wavelength of response of resonant-cavity-enhanced (RCE) photodetectors shifts according to the change of the refractive index, and the response of a given optical wavelength simultaneously changes.With an increasing As composition of ln(1-x)Ga(x)As(y)P(1-y) and the spacer thickness, the nonlinear effect increases, but the -1-dB input saturation optical power and the -1-dB saturation photocurrent decrease. Bistable-state operation occurs when the input optical power is in the proper bistable region.

Improved performance in organic light emitting diodes with a mixed electron donor-acceptor film involved in hole injection

Organic light emitting diodes using a mixed layer of electron acceptor 3, 4, 9, 10 perylenetetracarboxylic dianhydride and electron donor copper phthalocyanine (PTCDA:CuPc) on indium tin oxide (ITO) anodes were fabricated. The device properties were found to be strongly dependent on the thickness of the PTCDA:CuPc film: both the power efficiency and the driving voltage of the device were optimized with a thickness of PTCDA:CuPc ranging from 10 to 20 nm. As compared to the conventional ITO/CuPc hole injection structure, the ITO/PTCDA:CuPc hole injection structure could remarkably enhance both the luminance and the power efficiencies of devices. A mechanism of static-induced, very efficient hole-electron pairs generation in mixed PTCDA:CuPc films was proposed to explain the experimental phenomena. The structural and optical properties of PTCDA:CuPc film were examined as well. (c) 2007 American Institute of Physics.

Effect of ultraviolet light on hybrid zinc oxide polymer bulk heterojunction solar cells

Compared to conjugated polymer poly[2-methoxy-5- (3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) solar cells, bulk heterojunction solar cells composed of zinc oxide (ZnO) nanocrystals and MDMO-PPV have a better energy conversion efficiency, However, ultraviolet (UV) light deteriorates the performance of solar cells composed of ZnO and MDMO-PPV. We propose a model to explain the effect of UV illumination on these ZnO:MDMO-PPV solar cells. According to this model, the degradation from UV illumination is due to a decrease of exciton dissociation efficiency, Our model is based on the experimental results such as the measurements of current density versus voltage, photoluminescence, and photocurrent.

Violet electroluminescence of AlInGaN-InGaN multiquantum-well light-emitting diodes: Quantum-confined stark effect and heating effect

Electroluminescence (EL) from AlInGaN-InGaN multiquantum-well violet light-emitting diodes is investigated as a function of forward bias. Two distinct regimes have been identified: 1) quantum-confined Stark effect at low and moderately high forward biases; 2) heating effect at high biases. In the different regimes, the low-temperature EL spectra exhibit different spectral features which are discussed in detail.

Thermal lensing effect in ridge structure InGaN multiple quantum well laser diodes

Time-resolved light-current curves, spectra, and far-field distributions of ridge structure InGaN multiple quantum well laser diodes grown on sapphire substrate are measured with a temporal resolution of 0.1 ns under a pulsed current condition. Results show that the thermal lensing effect clearly improves the confinement of the higher order modes. The thermal lens leads to a lower threshold current for the higher order modes, a higher slope efficiency, and a change in the lasing mode of the device. The threshold current for the higher modes decreases by about 5 mA in every 10 ns in a pulse, and the slope efficiency increases by 7.5 times on the average when higher modes lase. (c) 2006 American Institute of Physics.