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Optimal target-sputtering mode for Aluminum Nitride thin film deposition by high power pulse magnetron sputtering (HPPMS)

Gallium oxide (Ga2O3) has received much attention in recent years, for its ultra-wide bandgap (4.5-4.8 eV), high theoretical breakdown field (8 MV/cm), low cost and large-size native substrate. Benefiting from the high current handling capability, Ga2O3 vertical Schottky barrier diodes (SBDs) are much more desirable for power switching applications. However, there is a high-density interface state at the dielectric/Ga2O3 interface in the vertical β-Ga2O3 SBDs, resulting in high reverse leakage current and poor breakdown characteristics. To overcome the aforementioned problem, a high-performance vertical β-Ga2O3 Schottky Barrier Diode (SBD) with a novel homologous air bridge field plate (HABFP) is reported. An air space is constructed at the foot of the anode, using a double dielectric layer with 20 nm SiO2 and 300 nm SiNx by self-aligned wet etching. The HABFP structure effectively suppresses the high peak electric field at anode foot, since the anode metal is separated from the dielectric/Ga2O3 interface. Compared with devices with a conventional field plate (CFP) using single SiNx or SiO2, the fabricated HABFP β-Ga2O3 SBD demonstrates a much higher breakdown voltage (Vbr) of 1100 V, while maintaining a relatively low specific on-resistance (Ron,sp) of 1.83 mΩ·cm2. Besides, the mechanism of the novel HABFP structure on the performance of β-Ga2O3 SBD is also analyzed, indicating that HABFP structure is a simple and effective termination technique.

This study was conducted to describe a prenatal case of congenital hydrocephalus and hemivertebrae with a 6q terminal deletion and to investigate the possible correlation between the genotype and phenotype of the proband. We performed an array-based comparative genomic hybridization (aCGH) analysis on a fetus diagnosed with congenital hydrocephalus and hemivertebrae. The deletion, spanning 10.06 Mb from 6q25.3 to 6qter, was detected in this fetus. The results of aCGH, karyotype and fluorescent in situ hybridization (FISH) analyses in the healthy parents were normal, which confirmed that the proband’s copy- number variant (CNV) was de novo. This deleted region encompassed 97 genes, including 28 OMIM genes. We discussed four genes (TBP, PSMB1, QKI and Pacrg) that may be responsible for hydrocephalus while the T gene may have a role in hemivertebra. We speculate that five genes in the 6q terminal deletion region were potentially associated with hemivertebrae and hydrocephalus in the proband.

We investigated the impact of early enteral nutrition (EEN) and parenteral nutrition (PN) on prealbumin (PA) and high-sensitivity C-reactive protein (hs-CRP) in patients after gastric cancer surgery. Sixty-eight selected patients undergoing gastric cancer surgery were randomly divided into the EEN (N = 34) and PN (N = 34) groups. Body weight (BW), serum albumin (ALB), transferrin (TF), PA, hs-CRP, length of hospital stay, cost of postoperative nutritional support, and incidence of complications were compared between groups. On postoperative day 7, the BW, TF, ALB, and PA for both groups were significantly decreased compared with the values obtained on preoperative day 1 (P0.01). A significant decrease was observed in TF and PA in the PN group compared with the EEN group (P0.01). There was no significant difference in BW and ALB between the two groups (P0.05). The hs-CRP level of both groups was significantly higher than on preoperative day 1. There was a significant increase in hs-CRP in the PN group compared with the EEN group (P0.01). The anal exhaust time, length of hospital stay, and nutritional support cost were significantly shorter or lower in the EEN group than in the PN group (P0.01). There was no significant difference in the incidence of complications between the two groups (P0.05). EEN helps regulate the postoperative response of patients after gastric cancer surgery, promotes rehabilitation, and accelerates the recovery of gastrointestinal function. Furthermore, EEN has the advantage of being inexpensive.

The impact of early enteral nutrition (EEN) on clinical outcomes of gastric cancer patients was investigated. Three hundred pa-tients undergoing gastric cancer surgery from July 2010 to May 2014 were randomly divided into experimental and control groups (n = 150/group). Experimental group patients received enteral nutrition in water during the early postoperative period. Control group patients received conventional perioperative treatment. Patients' clinical outcomes, post-operative immune function, and nutritional statuses were compared, which revealed that the postoperative fever duration (80.2 ± 6.0 vs 88.1 ± 8.1 h, P0.05), anal exhaust time (78.8 ± 9.3 vs 85.3 ± 8.4 h, P0.05), and length of hospitalization (7.73 ± 2.13 vs 9.77 ± 1.76 days, P0.01) differed significantly. Treatment costs in thousands of dol-lars were 31.24 ± 3.21 for the experimental group and 35.61 ± 2.32 for the control group; this difference was statistically significant (P0.01). The incidence of postoperative complications did not significantly differ between the experimental and control groups [14.0% (21/150) vs 17.3% (26/150), P0.05]. At postoperative days 3 and 7, the CD3(+), CD4(+), natural killer cell, albumin, and prealbumin levels and CD4(+)/CD8(+) ra-tio were significantly higher in the experimental group than the control group (all P0.05). CD8(+) cell counts were significantly lower in the experimental group than the control group (P0.05). Postsurgical oral EEN can improve nutritional status and immune function and promote early recovery of intestinal function in patients with gastric cancer.

We report the fabrication and characterization of highly responsive ZnMgO-based ultraviolet (UV) photodetectors in the metal–semiconductor–metal (MSM) configuration for solar-blind/visible-blind optoelectronic application. MSM devices were fabricated from wurtzite Zn1–xMgx O/ZnO (x ∼ 0.44) thin-film heterostructures grown on sapphire (α-Al2O3) substrates and w-Zn1–xMgx O (x ∼ 0.08), grown on nearly lattice-matched lithium gallate (LiGaO2) substrates, both by radio-frequency plasma-assisted molecular beam epitaxy (PAMBE). Thin film properties were studied by AFM, XRD, and optical transmission spectra, while MSM device performance was analyzed by spectral photoresponse and current–voltage techniques. Under biased conditions, α-Al2O3 grown devices exhibit peak responsivity of ∼7.6 A/W at 280 nm while LiGaO2 grown samples demonstrate peak performance of ∼119.3 A/W, albeit in the UV-A regime (∼324 nm). High photoconductive gains (76, 525) and spectral rejection ratios (∼103, ∼104) were obtained for devices grown on α-Al2O3 and LiGaO2, respectively. Exemplary device performance was ascribed to high material quality and in the case of lattice-matched LiGaO2 films, decreased photocarrier trapping probability, presumably due to low-density of dislocation defects. To the best of our knowledge, these results represent the highest performing ZnO-based photodetectors on LiGaO2 yet fabricated, and demonstrate both the feasibility and substantial enhancement of photodetector device performance via growth on lattice-matched substrates. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Based on the theory of thermal effect, the temperature rise, deformation and the deformation of periodically polarized region are simulated. The theory of nonlinear transformation, the effect of thermal effect on nonlinear effect is analyzed.Based on the oscillation theory of the laser resonator, the laser resonator was proposed to be constructed, and the influence of the laser resonator and the optical parametric oscillation was analyzed to describe the optical parametric oscillation process of Nd:MgO:PPLN crystal construction more accurately.The thermal effect of the original dynamic model of OPO in the inner cavity was modified to better reflect the actual situation of the compound self-optical parametric oscillator. The experimental study of the future self-optical parametric oscillator provided a design idea and laid a theoretical foundation for the subsequent experiments.

Low expression of myeloid/lymphoid or mixed-lineage leukemia 3 (MLL3) is reportedly associated with gastric cancer and tumor progression. The purpose of this study was to examine the expression of MLL3 in tissue samples of patients with gastric cancer and to analyze the relationship between MLL3 protein expression and clinical records. Using immunohistochemical staining and Kaplan-Meier analysis for MLL3 in gastric cancer patients, we found that low expression of MLL3 had a significant relationship with a low survival rate compared to positive MLL3 expression in the patients analyzed (P

Opening and tuning of the band gap of bilayer graphene (BLG) is of particular importance for its utilization in nanoelectronics. We presented here the electronic structures of two types of stoichiometrically half-fluorinated BLGs (i.e. C2Fs) as well as those under biaxial compressive and tensile strains. Our results reveal that both C2Fs are semiconductor with large direct band gaps in their unstrained configurations. Under biaxial compressive strains, the band gaps of both C2Fs can be reduced. However, by applying biaxial tensile strains, both C2Fs undergo a direct-to-indirect band gap transition. Electronic nature of the strain-tuned band gaps has been discussed.

We have studied the electronic and magnetic properties of fluorinated graphene with different coverage of fluorine using first-principles calculations based on the density functional theory. The atomic structures, adsorption energies, and electronic structures of fluorinated graphene are investigated. Our results show that the electronic and magnetic properties of fluorinated graphene sheet exhibit strong dependence on the degree of fluorination. A precise adsorption of fluorine enables a tuning of the band gap from 0 to ∼3.13 eV as well as a transformation from nonmagnetic semimetal to nonmagnetic/magnetic metal, or to magnetic/nonmagnetic semiconductor. Therefore, our study suggests that the property of graphene can be modified by absorbing different amounts of fluorine.

We report on the electrical and optical properties of InGaN based light emitting diodes (LEDs) utilizing Ga doped ZnO (GZO) grown by MBE as a highly transparent contact p -electrode (GZO-LEDs). For comparison, the LEDs with semi-transparent thin Ni/Au (5nm/5nm) current spreading layers were also fabricated on the same wafer (Ni/Au-LEDs). Pulsed electroluminescence measurements revealed that the relative external quantum efficiency (EQE) of the GZO-LED is 1.7-2 times higher than that of Ni/Au-LED at high current densities. Moreover, GZO-LEDs can withstand much higher current densities (4700 A/cm2) than the Ni/Au LEDs (3500 A/cm2) under pulsed mode. Unpackaged GZO-LEDs with 200 μm diameter showed negligible light output degradation for up to 30 mins under CW current of 100 mA (corresponding to a 318 Acm-2 current density), while the light output for Ni/Au-LEDs was reduced by 85% after only 5 mins of operation due to the severe current crowding effect (or current filamentation). (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In both light emitting devices such as light emitting diodes (LEDs), and light absorbing devices such as solar cells (also photodetectors), which are gaining considerable interest for their energy saving and energy production capability, respectively, a compromise must be struck between the need to increase the light emitting/absorbing area/potential and the need for low series resistance of the metal contact grid. This undesirable compromise can be mitigated by using transparent conducting oxides (TCOs), which heretofore have been dominated by ITO (indium tin oxide—an In-rich alloy of indium oxide and tin oxide). Due to the expected scarcity of Indium used in ITO, efforts are underway to develop indium-free TCOs for the above-mentioned devices as well as flat panel displays. ZnO heavily doped with Ga or Al (GZO or AZO) is becoming a very attractive candidate for future generation TCOs. GZO and AZO as well as multilayer TCOs consisting of two TCO layers with a thin metal layer in between have been widely investigated for LEDs and solar cells to enhance device performance. This article succinctly reviews the latest developments in and properties of TCOs, particularly in relation to thin film transparent electrode applications for LEDs and solar cells. Pertinent critical issues and possible solutions are provided as well.

Light-emitting diodes (LEDs) have become quite a high-performance device of late and are revolutionizing the display and illumination sectors of our economy. Due to demands for better performance and reduced energy consumption there is a constant race towards converting every single electron hole pair in the device to photons and extracting them as well while using only the minimum required voltage. This raises the bar on GaN-based LEDs in terms of elimination of nonradiative recombination processes not just at low but just as importantly if not more at very high injection levels needed for high brightness sources, and design of heterostructures for efficient electron and hole recombination without carrier loss and voltage/photon energy conversion loss. The haunting efficiency droop observed in GaN-based LEDs at high injection levels has been attributed to nonradiative Auger recombination, but can be simply explained by electron spillover. Investigations of quantum well (QW) InGaN LED structures with different barrier heights, widths, and doping suggest that limited hole transport in the active region and the resulting electron spillover is responsible for efficiency droop at high injection levels. In this paper, highly critical, demanding, and challenging nature of high-efficiency high-brightness LEDs, in particular the basics surrounding the internal quantum efficiency of LED structures and the ongoing research/development, will be discussed.

We report on the electrical and optical properties of InGaN based light emitting diodes (LEDs) utilizing Ga doped ZnO (GZO) grown by molecular beam epitaxy (MBE) as a highly transparent contact p-electrode (GZO-LEDs). For comparison, the LEDs with semi-transparent thin Ni/Au (5/5 nm) current spreading layers were also fabricated on the same wafer (Ni/Au-LEDs). Unpackaged GZO-LEDs with 200 μm diameter showed negligible light output degradation for up to 30 min under CW current of 100 mA (corresponding to a 318 A/cm 2 current density), while the light output for Ni/Au-LEDs was reduced by 85% after only 5 min of operation due to the severe current crowding effect (or current filamentation). Pulsed electroluminescence (EL) measurements revealed that the GZO-LEDs exhibit 50% higher EL intensity for the same current levels.

We have investigated efficiency droop in InGaN-based blue LEDs by considering radiative, nonradiative, and carrier spillover processes in the context of internal quantum efficiency (IQE) vs. injection current. If relied on fitting only, both the Auger recombination and an empirical formula for carrier spillover are consistent with experiments. However, the dependence of IQE on quantum well parameters and lack of droop in optical pumping experiments support the notion that carrier spillover is the main mechanism in play.

The aim of this study was to investigate the changes in cerebral blood flow velocity (CBFV) and its relation to apolipoprotein E (apoE) epsilon4 allele in mild cognitive impairment (MCI). Thirty MCI and 30 controls were assessed using Mini-Mental State Examination (MMSE) and Cambridge Cognitive Examination-Chinese version (CAMCOG-C), and then insonated in the anterior (ACA), middle (MCA) and basilar (BA) cerebral arteries using transcranial Doppler ultrasonography. Compared with controls, MCI showed significant decreases in the mean (V(m)), systolic (V(s)) and diastolic (V(d)) CBFV, bilaterally in MCA and ACA (P < 0.05-0.001), but not in BA. Compared with 17 apoE epsilon4 allele non-carriers, 13 carriers in MCI showed significant CBFV decreases, bilaterally in MCA (P < 0.05-0.001). Our findings, the decreased CBFV in apoE epsilon4 allele carriers with MCI, suggest that a large sample and longitudinal study in CBFV and cognitive changes may have the implications on early diagnosis of Alzheimer's disease.

High-power 3 μm-wide narrow-ridge-waveguide lasers with ten stacks of electronic vertically coupled InAs/GaAs quantum dots in the active region were demonstrated. Unlike that from conventional uncoupled InAs quantum dot lasers, a narrow lasing spectrum was observed because the carriers tunneled in the vertical direction. Continuous-wave operation in single lateral mode yielded a kink-free output power of 320 mW with an efficiency of 0.46 W/A , and a sensitivity of lasing wavelength to temperature of 0.28 nm/K.

Dilute nitride semiconductors are a topic of major current research interest owing to the novel physics induced by the incorporation of N in small percentages of composition. Related research has been further motivated by the favourable characteristics for device applications of the resultant materials, particularly represented by GaInNAs quaternary compounds as active materials in the 1.3–1.6 µm wavelength range. Whilst 1.3-µm GaInNAs/GaAs materials and devices are now reaching a level of maturity, the extension of these structures to around 1.55 µm is still in its infancy. The authors report optical studies of 1.55-µm GaInNAs/GaAs heterostructures of varying characteristics, all grown by molecular beam epitaxy. As the addition of N complicates the local structure and optical properties in this material system, the PL mechanisms are clarified by detailed PL excitation (PLE) spectra. Whereas all the measured samples exhibit strong PL at room temperature, the electronic structure is quite different between samples grown under different conditions. Some demonstrate clearly standard 2-D quantum well (QW) electronic states and some demonstrate evidence of phase-separated quantum-dot-like (QD) structures.

Aberration-corrected scanning transmission electron microscopy images of the In0.15Ga0.85N active region of a blue light-emitting diode, acquired at ~0.1% of the electron dose known to cause electron beam damage, show no lateral compositional fluctuations, but do exhibit one to four atomic plane steps in the active layer’s upper boundary. The area imaged was measured to be 2.9 nm thick using position averaged convergent beam electron diffraction, ensuring the sample was thin enough to capture compositional variation if it was present. A focused ion beam prepared sample with a very large thin area provides the possibility to directly observe large fluctuations in the active layer thickness that constrict the active layer at an average lateral length scale of 430 nm.

High quality w-MgxZn1-xO thin films were grown epitaxially on c-plane sapphire substrates by plasma-assisted Molecular Beam Epitaxy. ZnO thin films with high crystalline quality, low defect and dislocation densities, and subnanometer surface roughness were achieved by applying a low temperature nucleation layer. By tuning Mg/Zn flux ratio, wurtzite MgxZn1-xO thin films with Mg composition as high as x=0.46 were obtained without phase segregation. Metal- Semiconductor-Metal (MSM) photoconductive and Schottky barrier devices with interdigitated electrode geometry and active surface area of 1 mm2 were fabricated and characterized. Resultant devices showed ~100 A/W peak responsivity at wavelength of ~260nm. We also report on cubic rock salt c-MgxZn1-xO thin films, following a non-traditional approach on MgO substrates, to demonstrate solar-blind photoresponse in MSM photodetectors, realizing a peak responsivity of 460 A/W (@ 250 nm) and 12.6 mA/W (@ 240nm) for mixed phase and single crystal films, respectively. A specific focus of the work is on identifying the impact of various growth parameters on the performance of the c- MgZnO detectors.

We demonstrate a critical effect of a metal-to-oxygen ratio on the electrical, optical, and structural properties of ZnO films heavily doped with Ga (carrier concentration in the range of 1020–1021 cm–3) grown by plasma-assisted molecular beam epitaxy. The as-grown layers prepared under the metal-rich conditions exhibited resistivities below 3 × 10–4 Ω cm and an optical transparency exceeding 90% in the visible spectral range as well as a large blue shift of the transmission/absorption edge attributed to the Burstein–Moss shift of the Fermi level deep into the conduction band, indicating high donor concentration. In contrast, the films grown under the oxygen-rich conditions required thermal activation and showed inferior properties. Furthermore, electrical measurements point to the nonuniform depth distribution of free carriers. An oxygen-pressure-dependent surface disordering is suggested to be responsible for the drastic effect of the metal-to-oxygen ratio on the film properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The optical absorption coefficient of Cd1−yZny Te near the fundamental band edge was measured at room temperature using transmission spectroscopy. Like in other II–VI semiconductors, it was found that the absorption coefficient exhibits an exponential dependence on incident photon energy according to Urbach’s rule. It was also found that the exponential parameters depend on composition, y, of Cd1−y ZnyTe. A technique is described for determining the composition of Cd1−y ZnyTe from optical transmission spectroscopy. This technique has been implemented in the manufacturing of Cd1−yZnyTe substrates for lattice matched epitaxial growth of HgCdTe.

Continuous large-broad laser gain spectra near 1.3 /spl mu/m are obtained using an active region of electronic vertically coupled (EVC) InAs-GaAs quantum dots (QDs). A wide continuous electroluminescence spectrum, unlike that from conventional uncoupled InAs QD lasers, was obtained around 230 nm (below threshold) with a narrow lasing spectrum. An internal differential quantum efficiency as high as 90%, a maximum measured external differential efficiency of 73% for a stripe-length of L=1 mm, and a threshold current density for zero total optical loss as low as 7 A/cm/sup 2/ per QD layer were achieved.

This paper presents the numerical simulation of the evolution of shock wave propagating through the magnetic helmet streamer region and further out along the current sheet. It was obtained by using a set of complete projected-characteristic boundary conditions at the inner (1.1 R s ) and outer (62 R s ) boundaries in the solar meridian. Main results reveal that (1) the convection effect of the background wind speed on the propagation of shock wave is significant, especially in the range of ≤ 60 R s ; (2) a dip of flow speed is formed in the magnetic helmet region and after that, it is weakened in the current sheet region; (3) two high-speed belts appear near the two sides of the magnetic helmet when this is stretched outward; (4) a high-density ring displaces behind the shock surface and could be torn when it moves from the magnetic helmet into the current sheet region.

By using aberration corrected scanning transmission electron microscopy we have found no small scale lateral In composition fluctuations exist in the In0.15Ga0.85N active region of a light emitting diode. Images were acquired at 2% of the electron dose known to create electron beam damage, so the acquired images reflect the intrinsic structure of the InGaN active region. Position averaged convergent beam electron diffraction reveals the local sample thickness where images were acquired is 4.8 nm, eliminating the possibility that the absence of composition variation was observed due to projection through a thick sample. In addition, 2-3 atomic layer steps were observed in the top surface of In0.08Ga0.92N layers and the In0.15Ga0.85N active layers, providing a possible mechanism for lateral carrier confinement.

We report on the effects of metal organic epitaxy grown GaN templates with different surface morphologies, achieved under different chamber pressures of 200 and 400 Torr, on the electrical properties of GZO. For as-grown GZO layers with electron concentration above 1020 cm-3 grown on either 200-Torr p-GaN or 400-Torr p-GaN templates, the electron concentration is temperature-dependent as opposed to temperature-independence for GZO/a-sapphires, which demonstrates that the underlying GaN layers affect the GZO electrical properties measured by Hall method. By annealing in nitrogen environment or by inserting a thick ZnO buffer layer, the effects of the underlying GaN layers on GZO electrical properties can be eliminated paving the way for accurate determination of electrical properties. All three annealed GZO layers grown on 200-Torr p-GaN, 400-Torr p-GaN, and a-sapphire, exhibited comparable electron mobilities (~50 cm2/V·s at 15 K and ~41 cm2/V·s at 300 K) and similar temperature dependences while their electron concentrations are different (5.1×1020, 7.1×1020, and 9.2×1020 cm-3) due to the substrate-caused differences in GZO growth mode, structure, etc. By means of simulations, ionized impurity scattering was found to be the dominant scattering mechanism in the range of 15-330 K for GZO when electron concentration is higher than 5×1020 cm-3. Although other scattering events caused by defects and structures are weaker than the ionized impurity scattering, the electrical properties could be still slightly improved by finding more optimized growth conditions to eliminate defects and/or to improve crystal quality.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

N-type GaN exhibits upward, near-surface band bending that can be decreased by generating a surface photovoltage (SPV). Fitting SPV measurements with a thermionic model based on the emission of charge carriers over the nearsurface barrier provides information about the band bending in dark. We have studied the temperature dependent SPV behavior from a Si-doped, n-type GaN sample grown by hydride vapor phase epitaxy in order to determine how the magnitude of band bending changes at higher temperatures. We have measured the effect of temperature and oxygen on the steady-state SPV behavior, where oxygen is photo-adsorbed on the surface under band-to-band illumination in an air/oxygen ambient more efficiently at higher temperatures. As predicted, the intensity-dependent SPV measurements performed at temperatures between 295 and 500 K exhibit a decrease in the maximum SPV with increasing temperature. When illumination ceases, the band bending then begins to restore to its dark value with a rate proportional to the sample temperature, which also fits a thermionic model.

We have found composition variations along the growth direction within regions of nominally constant indium composition in InGaN light emitting diode structures grown by metal-organic chemical vapor deposition using atomic resolution Z-contrast imaging in a scanning transmission electron microscope (STEM). Within 60 nm thick nominally In 0.01 Ga 0.99 N layers, we found periodic enhancements in the indium concentration into 4 bands separated by 11 nm. Energy dispersive spectroscopy spectrum imaging confirmed that the higher intensity in the high angle annular dark field (HAADF) Z-contrast STEM images was in fact caused by locally higher indium concentration. We observed no lateral indium composition fluctuations.

We report on the effects of substrate temperature and surface morphology of p-GaN templates on the properties of ZnO:Ga (GZO) layers grown by plasma-assisted molecular beam epitaxy. Substrate temperature varying from 200 °C to 450°C was found to have only a moderate effect on the electrical properties of GZO films but it greatly affects the surface morphology of the GZO films. The surface morphology and growth mode of GZO were also found to be considerably affected by the surface morphology of underlying p-GaN templates. On p-GaN templates with a smooth surface (RMS = 0.4 nm) featured by clear atomic steps, GZO layers grew in 2D growth mode and exhibited smooth surfaces with RMS roughness of 2 nm. In contrast, on p-GaN without clear atomic steps but having comparable surface roughness of 0.6 nm, GZO layers grew in 3D growth mode and exhibited rough surface (RMS roughness of ~17.0-20.0 nm). The results of surface roughness are consistent with those from TEM measurements. The lowest resistivity of ~2.3×10 -4 Ω·cm for as-grown GZO layers has been achieved at substrate temperature of 350°C, while the data for 2D GZO layers was affected by a parallel conduction channel from underneath GaN and require further studies. Although the differences in electrical properties and surface morphology existed, the GZO layers grown on different p-GaN templates showed optical transparency higher than 90% in the visible spectral range. The performance of 3D GZO layers as p-electrode was tested in InGaN light emitting diodes.

Epitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400 °C under metaland oxygen-rich conditions in terms of metal-to-reactive oxygen ratio by plasma-assisted molecular beam epitaxy (MBE). Several atomic force microscopy (AFM) techniques were used to characterize the surface morphology and electrical properties of these GZO films in ambient conditions. Local I-V spectra indicate that layers grown under both O-rich and metal-rich conditions are highly resistive until a relatively high voltage sweep (±12 V) is used. After removal of an insulating surface layer, conduction is possible at lower voltages, but eventually the film resistivity increases and it again becomes insulating. In addition to local I-V spectra, local charge injection and subsequent surface potential measurements were used to probe surface charging characteristics. For charge injection experiments, a reverse-bias voltage is applied to the sample while scanning in contact mode with a metallized tip. The resultant change in surface potential due to trapped charge is subsequently observed using scanning Kelvin probe microscopy (SKPM). The layers deposited in a metal-rich environment demonstrate the expected behavior, but the O-rich layers show anomalous negative and positive charging. Finally, surface photovoltage (SPV) measurements using above-bandgap UV illumination were performed. The GZO layers produce SPV values of 0.4 to 0.5 eV, where the films deposited in an O-rich environment have slightly higher SPV values and faster restoration.

InGaN light-emitting diodes (LEDs) utilizing ZnO layers heavily doped with Ga (GZO) as transparent p -electrodes were fabricated and their characteristics were demonstrated to be superior to those of LEDs with metal Ni/Au electrodes. Highly conductive and highly transparent GZO films were grown on p -GaN contact layers of the LED structures by plasma-assisted molecular beam epitaxy under metal-rich conditions. The c and a lattice constants of GZO were found to be close to the bulk values, indicating small lattice distortion of GZO. The as-grown GZO films showed resistivities as low as 2.2-2.9×10 -4 Ω cm. Upon rapid thermal annealing at the optimum temperature of 675 °C, the resistivity decreased reaching a value of ~1.9×10-4 Ω cm. Unlike the LEDs with Ni/Au contacts, the LEDs with GZO electrodes showed no filamentation and very uniform light emission at high current densities. The peak value of the relative external quantum efficiency for the LEDs with GZO contacts has substantial improvement compared with that for the LEDs with Ni/Au contacts. Under pulsed excitation mode, GZO-LEDs withstood current densities up to 5000 A/cm 2 .

Dulwich OnView (DOV) is a museum blog magazine run by the Friends of Dulwich Picture Gallery (DPG) for the surrounding community in south London. It includes articles concerning both the gallery and the local community, helping to promote DPG in the process, in a fast-moving informal way that complements the official DPG website. For example, a competition for online artworks has been undertaken using DOV in association with a temporary exhibition of works by the 20th century British artist Paul Nash. This paper provides an overview of the progress of the blog, since its launch in January 2008, including statistical information. A redesign of the DOV blog has been undertaken in 2010, aimed at a better structuring of the increasing number of articles into categories and the integration between the more formal and static DPG website and the more informal and dynamic DOV website, with suitable interconnecting links. As part of the redesign process for the DOV website a usability review was conducted. DOV has also been part of a wider study, investigating a number of varied museum-based virtual communities in an art education context using the social science Community of Practice (CoP) framework.

The design optimization for 0.3- mu m channel CMOS technology at liquid-nitrogen temperature (77 K) is described. The tradeoff between circuit performance and reliability for deep-submicrometer CMOS devices at low-temperature operation is theoretically and experimentally examined. A simulator, which selects power-supply voltage and process/device parameters for low-temperature operation, has been developed. Based upon the simulated results, design optimization for low-temperature operation has been proposed to determine power-supply voltage and various process and device parameters. The optimized design has been demonstrated on a 0.3- mu m CMOS device, by utilizing electron beam (EB) lithography. Excellent device characteristics and a functional ring oscillator circuit have been obtained at 77 K. >

Aim This prospective study was designed to assess the feasibility of local anaesthesia for LigaSureTM haemorrhoidectomy in an outpatient setting. Method From April 2006 to March 2007, 207 consecutive patients (median age 42, 126 males) with grade III (147) and grade IV (60) haemorrhoids, underwent Milligan–Morgan haemorrhoidectomy with LigaSureTM under local anaesthesia (lidocaine 1%, mean dose 27 ± 1.7 ml) in an outpatient setting. Postoperative pain was assessed by a visual analogue scale (VAS). Results Two, three and four files were removed in 120, 51 and 36 patients. Mean operative time was 12 ± 5.2 min and mean blood loss was 3.4 ± 3.9 ml. The mean postoperative pain scores were 6.2 ± 2.1 for the maximal pain intensity and 6.1 ± 2.5 for the pain on defecation. All patients left hospital after surgery within 2 h and 33 (15.9%) required analgesics. They returned to normal daily activity after 12.2 ± 7.9 days including work (12.1 ± 7.8 days). The wounds had healed by 32.2 ± 9.1 days. At a follow-up of at least 6 months, only six cases of major bleeding had occurred and 24 patients had skin tags. The median satisfaction score was +2 (−2 to +3). Conclusion LigaSureTM haemorrhoidectomy under local anaesthesia in the outpatient setting is safe and effective.

For light emitting diodes (LEDs) to be used for general lighting, high efficiencies would need to be retained at high injection levels to meet the intensity and efficiency requirements. In this regard, it is imperative to overcome the observed drop in LED efficiency at high injection levels beyond that would be expected from junction temperature. The suggested genesis of efficiency degradation includes electron overflow or spillover, also suggested to be aided by polarization induced electric field, Auger recombination, current crowding, and elevated junction temperature. Setting the junction temperature aside, the degree to which or even whether each of these mechanisms plays a role is still under debate. We have undertaken a series of experiments to isolate, whenever possible, the aforementioned processes in an effort to determine the causes of efficiency loss at high injection levels. By using 1μs pulsed electrical injection with 0.1% duty cycle, we were able to minimize the effect of the junction temperature. By changing the design of the multiple quantum well region as well as by employing or not employing electron blocking layers, we demonstrated the important role that electron overflow plays on efficiency. Furthermore, by also exploring the same on non polar surfaces and observing any lack of dispersion in terms of the effect of the electron blocking layer we can conclude that the polarization induced field does not seem to play a major role. LEDs on non polar surface with no notable efficiency degradation, up to current densities of about 2250 Acm-2 used for measurements, have been obtained which seems to imply that Auger recombination up to these injection levels is not of major importance, at least in the structures investigated. The effect of current crowding on efficiency droop was investigated by comparing semitransparent Ni/Au p-contacts and transparent conducting oxide contacts (Ga-doped ZnO). Because the latter showed notably reduced efficiency degradation at high injection levels, we can conclude that current crowding plays a role as well.

A high-growth-temperature step used for the GaAs spacer layer is shown to significantly improve the performance of 1.3-μm multilayer InAs/GaAs quantum-dot (QD) lasers. The high-growth-temperature spacer layer inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics and hence improved laser performance. The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR) coated facets has been utilized to further reduce the threshold current and threshold current density ( J th ) for 1.3-μm InAs/GaAs QD lasers. Very low continuous-wave room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm 2 are achieved for a 3-layer device with a 1-mm long HR/HR cavity. For a 2-mm cavity the continuous-wave threshold current density is as low as 17 A/cm 2 at room temperature for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets. The high-growth-temperature spacer layers have only a relatively small effect on the temperature stability of the threshold current above room temperature. To further increase the characteristic temperature ( T 0 ) of the QD lasers, 1.3-μm InAs/GaAs QD lasers incorporating p-type modulation doping have been grown and studied. A negative T 0 and J th of 48 A/cm -2 at room temperature have been obtained by combining the high-growth-temperature GaAs spacer layers with the p-type modulation doping of the QDs.

The use of high growth temperature GaAs spacer layers is shown to significantly improve the performance of 1.3μm multi‐layer quantum dot lasers by preventing the formation of threading dislocations. As‐cleaved devices exhibit a cw room temperature (300K) threshold current density (Jth ) of 39 Acm−2 and operate up to 105°C. High reflectivity coated facet devices operate at 300K with a cw Jth of 17 Acm−2.

MBE growth of high quality diluted Nitride materials have been investigated. Photoluminescence intensity of high nitrogen content InGaAsN/GaAs SQW can be improved significantly by decreasing the growth temperature due to suppressd phase separation of InGaAsN alloy. The longest room temperature PL peak wavelength obtained in this study is 1.59 μm by increasing the nitrogen composition up to 5.3%. High performance ridge-waveguide InGaAsN/GaAs single quantum well lasers at wavelength 1.3 μm have been demonstrated. Threshold current density of 0.57 KA/cm 2 was achieved for the lasers with a 3-μm ridge width and a 2-mm cavity length. Slope efficiencies of 0.67 W/A was obtained with 1 mm cavity length. The cw kink-free output power of wavelength 1.3 μm single lateral mode laser is more than 200 mW, and the maximum total wallplug efficiency of 29% was obtained. Furthermore, monolithic MBE-grown vertical cavity surface emitting lasers (VCSELs) on GaAs substrate with an active region based on InGaAsN/GaAs double quantum wells emitting at 1304 nm with record threshold current density below 2 KA/cm 2 also have been demonstrated. The CW output power exceeds 1 mW with an initial slope efficiency of 0.15 W/A. Such low threshold current density indicates the high quality of InGaAsN/GaAs QW active region.

Results of Fourier transform photoluminescence (FTPL), X-ray diffraction (XRD), micro-Raman spectroscopy, and photoreflectance (PR) nondestructive characterization measurements of In/sub x/Ga/sub 1-x/As grown by molecular beam epitaxy (MBE) on semi-insulating InP:Fe substates are presented. FTPL identified recombination processes at low and room temperature and carrier types of InGaAs films through correlation of 4.2 K and 293 K PL emissions. XRD measurements determine the extent of film relaxation and the composition. The strained nature of the InGaAs films is suggested by the correlation of low temperature PL bandgap energy and XRD composition. GaAs-like LO and TO modes and an InAs-like LO mode are identified by Raman scattering. Room temperature PR and PL bandgap energies show correlation within experimental error. >

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

We report the use of laser light scattering (LLS) for the in situ detection of strained epitaxial layer relaxation. Strained layer superlattices (SLSs) of InGaAs/GaAs were prepared by molecular beam epitaxy. The rapid increase in the LLS signal was interpreted as increased surface roughness due to surface steps generated during InGaAs relaxation. The LLS signal was sharply peaked with respect to the azimuthal angle (the rotation angle between crystal axes and the detection axis), indicating the scattering comes primarily from α misfit dislocations which run parallel to the (011) direction. The growth time at which the LLS signal onset occurred, together with the InGaAs growth rate, yielded the critical layer thickness, hc. The hc value for SLSs of In0.17Ga0.83As/GaAs with thicknesses of 4.6/17 and 4.6/7.8 nm were 25 and 23 nm, respectively, and almost identical to values obtained for single InGaAs layers. The observed values of hc are greater than those calculated using the standard force‐balance model. ...

The formation and development of geospatial cognitive abilities are an important aspect of training geographic literacy of secondary students, because these abilities have vital significance for solving their own problems related to geography and its study. However, training geospatial cognitive abilities is currently quite weak in our secondary school's geography curriculum. Many secondary students now have low geospatial cognitive abilities. Remote sensing has a lot of advantages over other training in geospatial cognitive abilities. Therefore, how to use remote sensing in training geospatial cognitive abilities of secondary students should be given necessary importance. Based on the partition of essential factors of geospatial cognitive abilities, this study analyzed some advantages and summarized five teaching strategies integrating remote sensing in training geospatial cognitive abilities in our secondary education, which can provide applicable opinions and suggestions for developing geospatial cognitive abilities of secondary students.

Despite their large lattice mismatch (∼25%), epitaxial CaF2 films have been grown on single crystal Al(111) on Si(111) by low temperature molecular beam epitaxy. X‐ray diffraction shows that the orientations of the CaF2 are the same as those of the Al films, whether the orientations of the Al are the same rotated 180° or with respect to the underlying Si substrate. Furthermore, our successful fabrication of an epitaxial Al/CaF2/Al/Si(111) structure suggests that Al can be a useful conductor material in three‐dimensional device integration.

We have applied micro‐Raman spectroscopy to the analysis of structural quality of GaAs‐on‐Si where the GaAs growth was performed through openings in an amorphous mask. The presence of the symmetry forbidden transverse optic (TO) phonon band and line shape of the longitudinal optic (LO) phonon band have been used to extract information concerning the structural quality of microscopic regions of GaAs from the Raman spectra. The utility of TO to LO phonon intensity ratios as a measure of crystal quality has been corroborated by correlation to x‐ray rocking curve full width. The structural quality of selectively grown GaAs as determined from first‐order Raman ratios is found to degrade in the vicinity of the transition between single crystal and polycrystalline regions. This work also shows that post‐growth annealing significantly improves the quality of structures with minimum feature size as small as 2 μm.

Refractory metal gates have been studied for CMOS gate electrodes on ultra thin gate oxide due to its midgap work function, low resistivity and no gate depletion, etc. In particular, titanium nitride received most attention because of its process maturity and its good diffusion barrier properties for backend applications. Different TiN film properties are important when TiN is used as a gate material than when it is used for backend applications. One issue is the effect of TiN film impurities on the gate oxides and their high temperature stability since some high temperature processes are usually needed after gate formation. This paper reports the study of different TiN films used as MOS gate electrodes on ultra thin gate oxide and the effects of their impurities on gate oxide electrical performance. PVD TiN films deposited with different process conditions show different oxygen content, and different gate oxide properties were observed when these PVD TiN films were used as gate electrodes. On the other hand CVD TiN films deposited using different precursors also showed different impurities, including carbon, oxygen or silicon, which largely affect CVD TiN performance when used as gate material. The different TiN films were characterized by X-ray glancing angle reflection, XPS, SIMS and TEM, and the electrical properties were studied by I-V, C-V, charge to breakdown (Qbd) and ramp voltage breakdown tests on MOS capacitors. The results showed that the high purity TiN films provide stable gate material with small damage to the gate oxide, but impurities, especially oxygen, affect the gate oxide properties after high temperature anneal. However, due to the different TiN process capabilities, TiN films with impurities may still have advantages over pure TiN film in some cases of different MOS gate applications.