The effect of dislocations on the efficiency of InGaN/GaN solar cells

Two solar cells based on an InGaN/GaN p-i-n hetero-junction, but having different dislocation densities, were fabricated and characterized. The structures were grown on c-plane (0001) GaN-on-sapphire templates with different threading dislocation (TD) densities of 5×108 and 5×109 cm-2. Structural characterization revealed the presence of V-defects in the InGaN epilayer. Since each V-defect was associated with a TD, the structural as well as the optical properties worsened with a higher TD density in the GaN/sapphire template. It was also found that additional dislocations were generated in the p-GaN layer over the V-defects in the InGaN layer. Because of its superior structural quality, the peak external quantum efficiency (EQE) of the low TD density sample was three times higher than that of the high TD density sample. © 2013 Elsevier B.V.

The effect of clearance on shrouded and unshrouded turbines at two levels of reaction

In this paper, the effect of seal clearance on the efficiency of a turbine with a shrouded rotor is compared with the effect of the tip clearance when the same turbine has an unshrouded rotor. The shrouded versus unshrouded comparison was undertaken for two turbine stage designs one having 50% reaction, the other having 24% reaction. Measurements for a range of clearances, including very small clearances, showed three important phenomena. Firstly, as the clearance is reduced, there is a "break-even clearance" at which both the shrouded turbine and the unshrouded turbine have the same efficiency. If the clearance is reduced further, the unshrouded turbine performs better than the shrouded turbine, with the difference at zero clearance termed the "offset loss." This is contrary to the traditional assumption that both shrouded and unshrouded turbines have the same efficiency at zero clearance. The physics of the break-even clearance and the offset loss are discussed. Secondly, the use of a lower reaction had the effect of reducing the tip leakage efficiency penalty for both the shrouded and the unshrouded turbines. In order to understand the effect of reaction on the tip leakage, an analytical model was used and it was found that the tip leakage efficiency penalty should be understood as the dissipated kinetic energy rather than either the tip leakage mass flow rate or the tip leakage loss coefficient. Thirdly, it was also observed that, at a fixed flow coefficient, the fractional change in the output power with clearance was approximately twice the fractional change in efficiency with clearance. This was explained by using an analytical model. © 2014 by ASME.

Effect of ration on the growth and energy budget of Chinese longsnout catfish, Leiocassis longirostris Gunther

The effect of ration on growth and energy budget of Chinese longsnout catfish was investigated in a growth trial. Fish of initial body weight of 6.5 g were fed at six ration levels (RLs): starvation, 0.8%, 1.6%, 2.4%, 3.2% of body weight per day, and apparent satiation for 8 weeks. Fish were weighed biweekly to adjust feed amount. The results showed that specific growth rate in wet weight, protein and energy increased logarithmically with increased RLs. The relationship of specific growth rate in wet weight (SGRw, % day(-1)) and RL (%) was a decelerating curve: SGRw=-0.62+3.10 Ln(RL+1). The energy budget equation at satiation was: 100 IE=12.94 FE+5.50(ZE+UE)+40.07 HE+41.49 RE, where IE, FE, (ZE+UE), HE, RE are food energy, faecal energy, excretory energy, heat production and recovered energy respectively. Body composition was slightly but significantly affected by ration size except for protein content. The most efficient ration based on the relationship between RL and feed efficiency ratio in energy (FERe) was 1.8% of body weight per day.

Effect of CO on characteristics of AlGaN/GaN Schottky diode

Pt Schottky diode gas sensors for CO are fabricated using AlGaN/ GaN high electron mobility transistor ( HEMTs) structure. The diodes show a remarkable sensor signal (3 mA, in N-2; 2mA in air ambient) biased 2V after 1% CO is introduced at 50 degrees C. The Schottky barrier heights decrease for 36meV and 27meV in the two cases respectively. The devices exhibit a slow recovery characteristic in air ambient but almost none in the background of pure N2, which reveals that oxygen molecules could accelerate the desorption of CO and offer restrictions to CO detection.

Effect of annealing on photoluminescence properties of neon implanted GaN

The effect of thermal annealing on the luminescence properties of neon implanted GaN thin films was studied. Low temperature photoluminescence (PL) measurements were carried out on the samples implanted with different doses ranging from 10(14) to 9 x 10(15) cm(-2) and annealed isochronally at 800 and 900 degrees C. We observed a new peak appearing at 3.44 eV in the low temperative PL spectra of all the implanted samples after annealing at 900 degrees C. This peak has not been observed in the PL spectra of implanted samples annealed at 800 degrees C except for the samples implanted with the highest dose. The intensity of the yellow luminescence (YL) band noticed in the PL spectra measured after annealing was observed to decrease with the increase in dose until it was completely suppressed at a dose of 5 x 10(15) cm(-2). The appearance of a new peak at 3.44 eV and dose dependent suppression of the YL band are attributed to the dissociation of VGaON complexes caused by high energy ion implantation.

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.

Effect of Nitridation on Morphology, Structural Properties and Stress of AIN Films

We investigate effects of nitridation on AIN morphology, structural properties and stress. It is found that 3 min nitridation can prominently improve AIN crystal structure, and slightly smooth the surface morphology. However, 10 min nitridation degrades out-of-plane crystal structure and surface morphology instead. Additionally, 3-min nitridation introduces more tensile stress (1.5 GPa) in AIN films, which can be attributed to the weaker islands 2D coalescent. Nitridation for 10 min can introduce more defects, or even forms polycrystallinity interlayer, which relaxes the stress. Thus, the stress in AIN with 10 min nitridation decreases to -0.2 GPa compressive stress.

Effect of annealing on optical properties of InAs quantum dots grown by MOCVD on GaAs (100) vicinal substrates

Thermal annealing effect on InAs quantum dots grown on vicinal (100) GaAs substrates is studied in comparison with dots on exact (100) GaAs substrates. We find that annealing acts stronger effect on dots with vicinal substrates by greatly accelerating the degradation of material quality. as well as slightly increasing the blueshift of the emission wavelength and the narrowing of PL linewidth. It is attributed to the higher strain in the dots formed on the vicinal substrates.

Concentration effect of Mn2+ on the photoluminescence of ZnS : Mn nanocrystals

Mn-doped ZnS nanocrystals of about 3 nm diameter were synthesized by a wet chemical method. X-ray diffraction (XRD) measurements showed that the nanocrystals have the structure of cubic zinc blende. The broadening of the XRD lines is indicative of nanomaterials. Room temperature photoluminescence (PL) spectrum of the undoped sample only exhibited a defected-related blue emission band. But for the doped samples, an orange emission from the Mn2+ T-4(1)-(6)A(1) transition was also observed, apart from the blue emission. The peak position (600 nm) of the Mn2+ emission was shifted to longer wavelength compared to that (584 nm) of bulk ZnS:Mn. With the increase of the Mn2+ concentration, the PL of ZnS:Mn was significantly enhanced. The concentration quenching effect was not observed in our experiments. Such PL phenomena were attributed to the absence of Mn2+ pairs in a single ZnS:Mn nanocrystal, considering the nonradiative energy transfer between Mn2+ ions based on the Poisson approximation. (c) 2005 Elsevier B.V. All rights reserved.

Effect of oxidation on the optical and surface properties of AlGaN

The chemical properties of AlxGa1-xN surfaces exposed to air for different time periods are investigated by atomic force microscopy (AFM), photoluminescence (PL) measurement and X-ray photoelectron spectroscopy (XPS). PL and AFM results show that AlxGa1-xN samples exhibit different surface characteristics for different air-exposure times and Al contents. The XPS spectra of the Al 2p and Ga 2p core levels indicate that the peaks shifted slightly, from an Al-N to an Al-O bond and from a Ga-N to a Ga-O bond. All of these results show that the epilayer surface contains a large amount of Ga and Al oxides. (c) 2006 Elsevier B.V. All rights reserved.

Effect of disorder on self-collimated beam in photonic crystal

We report a numerical analysis of various types of disorder effects on self-collimated beam in two-dimensional photonic crystal. Finite-difference time-domain (FDTD) method is used to simulate the process by using a pulse propagation technique. The position disorders along the directions parallel and perpendicular to the incidence are considered. We show that random disorder along the perpendicular direction will have a lesser effect on the performance of the dispersion waveguides than those along the parallel direction. Furthermore, the self-collimation waveguide (SCW) has new characteristics when compared with the photonic crystal line defect waveguide. (c) 2006 Elsevier B.V. All rights reserved.

Effect of defects on optical phonon Raman spectra in SiC nanorods

Fabricated one-dimensional (1D) materials often have abundant structural defects. Experimental observation and numerical calculation indicate that the broken translation symmetry due to structural defects may play a more important role than the quantum confinement effect in the Raman features of optical phonons in polar semiconductor quantum wires such as SiC nanorods, (C) 1999 Elsevier Science Ltd. All rights reserved.

Effect of dopant on the uniformity of InAs self-organized quantum dots

Low-temperature photoluminescence studies have been performed on Si-doped and Be-doped self-organized InAs/GaAs quantum dot (QD) samples to investigate the effect of doping. When Si or Be is doped into the sample, a remarkable decrease in line-width is observed. We relate this phenomenon to a model that takes the Si or Be atoms as the nucleation centers for the formation of QDs. When Si or Be is doped, more small uniform quantum dots are formed. The result will be of significance for the application of self-organized InAs quantum dots in semiconductor devices.