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Introduction To study the expression of tumor associated macrophage (TAMs), inflammatory cytokines IL-1β (interleukin-lβ), TNF-α (tumor necrosis factor-α), IL-6 (interleukin 6) and IL-10 (interleukin 10) and its significance in different types of lymphoma in lymph node pathological tissue. Methods 106 cases of clinical pathology specimens of patients were collected from different types and different staging classifications. The expressions of tumor-associated macrophage and interleukin-1β (IL-1β), tumor nec.rosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-10 (IL-10) in lymphoma tissues were detected by immunohistochemical staining; Results Both CD68 and CSF-1R showed high expression in lymphoma tumor tissues. The positive rates of CD68 and CSF-1R in Ⅳ period patients was higher than Ⅱperiod (P Conclusion 1.CD68, tumor-associated macrophage phenotype, and CSF-1R were highly expressed in lymphoma tissues 2.The expression of CD68 was positively correlated with inflammatory cytokines. 3.TAMs were involved in tumor inflammatory microenvironment. Funded by Jiangsu Provincial Special Program of Medical Science (BL2012005) Disclosures No relevant conflicts of interest to declare.

GaN nanowires have been synthesized by ammoniating Ga2O3 oxide thin films. Ga2O3 films with a thickness of ~500 nm were deposited on quartz substrates by radio frequency magnetron sputtering. X-ray diffraction, scanning electronic microscope, transmission electronic microscope and high-resolution TEM results show that the majority of the GaN nanowires have a single-crystal hexagonal wurtzite structure with major axis [110] alignment. A minority are polycrystalline, composed of overlapped parallelepiped GaN nanocrystals, which gives the wires a herringbone topography. The diameters of the wires range from 10 to 90 nm and the lengths are up to 50 μm. The achievement of GaN nanowires by ammoniating Ga2O3 presents a novel method for synthesizing one-dimensional nanometre materials without the assistance of a template or a catalyst.

Pt/AlGaN/AlN/GaN Schottky diodes have been fabricated and characterized for H2 sensing. Platinum (Pt) with a thickness of 20nm was evaporated on the sample to form the Schottky contact. The ohmic contact, formed by evaporated Ti/Al/Ni/Au metals, was subsequently annealed by a rapid thermal treatment at 860°C for 30 s in N2 ambience. Both the forward and reverse current of the device increased greatly when exposed to H2 gas. The sensor's responses under different hydrogen concentrations from 500ppm to 10% H2 in N2 at 300K were investigated. A shift of 0.45V at 297K is obtained at a fixed forward current for switching from N2 to 10% H2 in N2. Time response of the sensor at a fixed bias of 0.5 V was also measured. The turn-on response of the device was rapid, while the recovery of the sensor at N2 atmosphere was rather slow. But it recovered quickly when the device was exposed to the air. The decrease in the barrier height of the diode was calculated to be about 160meV upon introduction of 10% H2 into the ambient. The sensitivity of the sensor is also calculated. Some thermodynamics analyses have been done according to the Langmuir isotherm equation.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 1019 cm−3. High resistivity GaN epitaxial material which is 1 × 109 Ωcm is achieved.

A novel multi-finger gate high electron mobility transistor (HEMT) is designed to reduce the peak electric field value at the drain-side gate edge when the device is at off-state. The effective gate length (Leff) of the multi-finger gate device is smaller than that of the field plate gate device. In this work, field plate gate, five-finger gate and ten-finger gate devices are simulated. The results of the simulation indicate that the multi-finger gate device has a lower peak value than the device with the gate field plate. Moreover, this value would be further reduced when the number of gate fingers is increased. In addition, it has the potential to make the HEMT work in a higher frequency since it has a lower effective length of gate.

The AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) structure was grown by metal organic chemical vapor deposition (MOCVD) on (0001) sapphire substrates. The electron transport properties were investigated by variable temperature Hall effect measurements. The fabricated devices with gate length of 0.8mum and gate width of 120 mum show a transconductance of 136mS/mm and maximum drain current of 435mA/mm. The small signal properties were also achieved with the current gain cut-off frequency (fT) of 5.8GHz and the maximum frequency of oscillation (fMAX) of 17GHz

We present calculation of critical voltage for AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layer. The calculation includes mechanical stress and relaxable energy in the GaN/AlGaN barrier layer. Under high voltage conditions, the high electric field results in an increase in stored relaxable energy. If this exceeds a critical value, crystallographic defects are formed. This degra- dation mechanism is voltage driven and characterized by a critical voltage beyond which non-reversible degradation takes place. The dependence of the GaN cap layer's thickness on the critical voltage has been discussed. The calculated results indicate that thicker GaN cap layer results in higher critical voltage.

In this paper, a numerical study of In x Ga1 − x N/Al y Ga1 − y N/GaN heterostructure is presented. The dependence of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) sheet densities on variables, such as In x Ga1 − x N layer thickness and In content, and Al y Ga1 − y N barrier layer thickness and Al content, are systematically investigated. The effect of P-type doping in In x Ga1 − x N on 2DEG and 2DHG sheet densities in this heterostructure is also studied. It is shown that the strong reverse electric field in In x Ga1 − x N cap layer contributes to the depletion of 2DEG at the Al y Ga1- y N/GaN interface. When In x Ga1 − x N layer thickness and In content increases, 2DEG sheet density decreases significantly. P-type doping shows less influence on 2DEG compared to the polarization electric field in In x Ga1 − x N layer. In addition, there exist critical values for all the variables beyond which 2DHG appears at the interface of In x Ga1 − x N/Al y Ga1 − y N. Once 2DHG appears, it will prevent 2DEG from being further depleted. With proper design of Al y Ga1 − y N layer, the coexistence of 2DEG and 2DHG in In x Ga1 − x N/Al y Ga1 − y N/GaN structure can be avoided, showing that this structure has great potential in the fabrication of enhancement mode (E-mode) high electron mobility transistors.

Lateral Schottky barrier diodes (SBDs) on AlGaN/GaN heterojunctions are fabricated and studied. The characteristics of the fabricated SBDs with different Schottky contact diameters and different Schottky-Ohmic contact spacings are investigated. The breakdown voltage can be increased by either increasing the Schottky-Ohmic contact spacing or increasing the Schottky contact diameter. However, the specific on-resistance is increased at the same time. A high breakdown voltage of 1400 V and low reverse leakage current below 20nA are achieved by the device with a Schottky contact diameter of 100 μm and a contact spacing of 40 μm, yielding a high V2BR/RON,sp value of 194 MW.cm−2.

A theoretical study of transconductance characteristics ( g m − V gs profile) of AlGaN/GaN high electron mobility transistors (HEMTs) with a graded AlGaN layer is given in this paper. The calculations were made using a self-consistent solution of the Schrodinger-Poisson equations and an AlGaN/GaN HEMTs numerical device model. Transconductance characteristics of the devices are discussed while the thickness and Al composition of the graded AlGaN layer are optimized. It is found that graded AlGaN layer structure can tailor device’s g m − V gs profile by improving polar optical phonon mobility and interface roughness mobility. Good agreement is obtained between the theoretical calculations and experimental measurements over the full range of applied gate bias.

In this paper, the enhanced performance of InGaN/GaN multiple quantum well solar cells grown on patterned sapphire substrates (PSS) was demonstrated. The short-circuit current (Jsc) density of the solar cell grown on PSS showed an improvement of 60%, compared to that of solar cells grown on conventional sapphire substrate. The improved performance is primarily due to the reduction of edge dislocations and the increased light absorption path by the scattering from the textured surface of the PSS. It shows that the patterned sapphire technology can effectively alleviate the problem of high-density dislocations and low Jsc caused by thinner absorption layers of the InGaN based solar cell, and it is promising to improve the efficiency of the solar cell.

This is a theoretical study of GaN-based heterostructures with unintentionally doped (UID) GaN channel layer and high-resistivity (HR) GaN buffer layer doped by deep acceptors. Self-consistent Schrodinger-Poisson (SP) numerical simulation shows that, by increasing the acceptor concentration in the HR buffer or narrowing the width of UID channel, the quantum confinement of two-dimensional electron gas (2DEG) is enhanced, while the sheet density of 2DEG is reduced. The tuning effect of 2DEG density is attributed to the depletion effect of negative space charges composed of ionized acceptors located in the region between the UID channel and the Fermi-level pinned region in the HR buffer. For the heterostructure without the UID channel, the 2DEG can be depleted as the acceptor concentration is beyond a critical value. However, by inserting a UID channel layer, the depletion effect of buffer acceptor on 2DEG density is reduced. To gain a further insight into the physics, a simple analytical model is developed, which reproduces well the results of SP simulation. By comparing our theoretical results with the experimental ones, a good agreement is reached, thus the validity of our model is verified.

An ultrathin AlN layer is inserted between the GaN channel and buffer in the fabrication of deep-submicrometer AlGaN/GaN high-electron-mobility transistors (HEMTs). The wide bandgap of AlN establishes a high back barrier and thus enhances the confinement of two-dimensional electron gas under high drain bias voltages. Owning to the effective suppression of short-channel effects in the device with a highly scaled gate length, the fabricated AlN back barrier HEMTs show better pinch-off quality, lower subthreshold current, lower drain-induced barrier lowering factor, and better high-frequency response than the reference device without an AlN back barrier.

Lithium tantalite (LiTaO3) thin films (∼0.5 μm ) have been successfully deposited on Pt (111)/ SiO 2 / Si (1 0 0) substrates by means of sol–gel spin-coating technology. Figures of merit for infrared detector were studied for the LiTaO3 thin films. There exists high figures of merit Fv of 2.1×10 −10 C cm/J and Fm of 2.4×10 −8 C cm/J because of the relative low dielectric constant (er) of 35 and high pyroelectric coefficient (γ) of 4.0×10 −8 C/cm 2 K of the films. The pyroelectric infrared detector fabricated by the LiTaO3 thin film exhibits a voltage reponsivity Rv of 4584 V/W at 20 Hz and a high specific detectivity D ∗ of 4.23×10 7 cm Hz 1/2 / W at 100 Hz .

AlGaN layers were grown on InAlN/AlN/GaN heterostructure with various temperatures. The two-dimensional electron gas density and mobility in heterostructure with high temperature AlGaN were deteriorated which is attributed to the reverse polarization field of AlGaN and the degradation of InAlN structural quality and surface morphology. A 2 nm low temperature GaN spacer was inserted to reduce the risk of InAlN degradation. The improved structures demonstrated an increase of two-dimensional electron gas density and mobility compared to the heterostructures without the GaN spacer, which results in the reduction of sheet resistance. Particularly, at 855 °C, an enhancement of mobility in the improved structure indicates that the heterostructure is relatively stable at this temperature. At higher temperature of 920 °C, significant increase of sheet resistance indicates a sharp degradation of InAlN quality.

The high Al content AlGaN epilayers have been obtained by metalorganic chemical vapor deposition (MOCVD), and the optical property has been investigated by photoluminescence (PL) spectroscopy. Longitudinal-optic (LO) phonon mode has been studied by Raman scattering. Further analysis shows that the edge dislocation is an important factor influencing optical quality of AlGaN epilayers, and it also shows that the correlation between the A 1 (LO) polar modes and the edge dislocation is intensive, which may be expected to become a characterization method of the related crystal defects.

The influence of pressure on the MOCVD grown InAlN/AlN/GaN heterostructure has been investigated by high-resolution X-ray diffraction, Hall measurement and atomic force microscopy. High pressure is beneficial to increase indium incorporation efficiency. The electrical properties of InAlN/AlN/GaN heterostructure become better with the pressure decreasing from 100 Torr to 50 Torr. Indium droplets tend to form on the InAlN surface at high pressure. The edge of the indium droplet is the Al-rich region while the interior is the In-rich region, demonstrated by the phase-contrast mode. Phase contrast across the V-defect is strong on the surface of InAlN grown at low pressure (50 Torr) whereas it is not evident at high pressure (100 Torr), indicating that large stress in the InAlN film will enhance the compositional variation.

We employ surface topographies and phase images to investigate InN nanodots. The samples are annealed at 450, 500 and 550 □. The results reveal that the statistical distributions of number density and mean size depend on annealing ambient. The behaviours of thermal annealing between InN films and InN nanodots are distinguishable: the alloying process of InN and GaN not only occurs in InN platelets, but also in InN nanodots once the samples are annealed at the growth temperature of InN nanodots, while the main change in InN films is the decomposition of InN into In droplets and N2.

Mg-doped InGaN was grown on unintentionally doped GaN layer, and Mg and defect behaviours in both GaN and InGaN : Mg were investigated through photoluminescence measurement at 7 K. Mg acceptor was found in unintentionally doped GaN after thermal annealing in N2 ambient, and Mg activation energy was estimated to be 200 meV and 110 meV for GaN and InGaN, respectively. Particularly, the ultraviolet band (3.0–3.2 eV) in the GaN layer was infrequently observed in the unannealed sample but quenched in the annealed sample; this band may be associated with oxygen-substituted nitrogen defects. Moreover, the measurement errors of photoluminescence and x-ray diffraction originated from strain were taken into account.

The conversion efficiency of In x Ga1−x N/GaN multiple quantum well solar cells is originally investigated in theory based on the ideal diode model and the ideal unity quantum well model. The results reveal that the conversion efficiency partially depends on the width of the quantum well and the thickness of the barrier region but is dominated by the number of quantum wells and indium content of In x Ga1−x N. The calculated results are found to be basically trustworthy by comparing with reported experimental results. An In0.15Ga0.85N/GaN multiple quantum well solar cell is successfully fabricated with a conversion efficiency of 0.2%. The main discrepancy between calculated and experimental results is the material quality and manufacturing technology which need to be improved.

A 2 μm high quality crack-free GaN film was successfully grown on 2-inch Si(111) substrates by metal organic chemical vapor deposition with a high temperature AlN/graded-AlGaN multibuffer and an AlN/GaN superlattice interlayer. It is found that the structures, as well as the thicknesses of the multibuffer and interlayer, are crucial for the growth of a crack-free GaN epilayer. The GaN(0002) XRD FWHM of the crack-free sample is 479.8 arcsec, indicating good crystal quality. An AlGaN/GaN heterostructure was grown and tested by Van der Pauw Hall measurement. The electron mobility of two-dimensional electron gas increases from 1928 cm2/V-s to 12277 cm2/V-s when the test-temperature decreases from room temperature to liquid nitrogen temperature. The electron mobility is comparable to that of AlGaN/GaN heterostructures grown on sapphire, and the largest value is obtained for an AlGaN/GaN/Si(111) heterostructure grown by metal organic chemical vapor deposition.

The influence of electric field on persistent photoconductivity in unintentionally doped n-GaN is investigated. It was found that under higher electric field the build-up course was slowed down while the decay course was accelerated. After a higher-voltage pulse, it was observed that the current dropped to a value lower than the dark current, and a current increase that lasted for thousands of seconds was observed. It is suggested that the above phenomena should be caused by the increase in capture rate of electron traps with electric field and are related to the Coulomb-repulsive characteristic of defects related to persistent photoconductivity.

Yellow and blue luminescence in undoped GaN layers with different resistivities are studied by cathodoluminescence. Intense yellow and blue luminescence bands are observed in semi-insulating GaN, while in n-GaN the yellow luminescence and blue luminescence bands are very weak. The stronger yellow and blue luminescences in semi-insulating GaN are correlated to the higher edge-type dislocation density. The scanning cathodoluminescence image reveals strong defect-related luminescence at the grain boundaries where the dislocations accumulate. It is found that the relative intensity of the blue luminescence band to the yellow luminescence band increases with the cathodoluminescence beam energies and is larger in n-GaN with a lower density of edge-type dislocations. An approximately 3.35 eV shoulder next to the near-band-edge peak is observed in n-GaN but not in semi-insulating GaN. A redshift of the near-band-edge peak with cathodoluminescence beam energy is observed in both samples and is explained by internal absorption.

Thermally stimulated luminescence spectroscopy has been applied to study the deep centres in unintentionally doped high resistivity GaN epilayers grown by the metal organic chemical vapour deposition method on c-sapphire substrates. Two trap states with activation energies of 0.12 and 0.62 eV are evaluated from two luminescence peaks at 141.9 and 294.7 K in the luminescence curve. Our spectroscopy measurement, in combination with more accurate first-principles studies, provided insights into the microscopic origin of these levels. Our investigations suggest that the lower level at 0.12 eV might originate from C-N, which behaves as a hole trap state; the deeper level at 0.62 eV can be correlated with V-Ga that corresponds to the yellow luminescence band observed in low-temperature photoluminescence spectra.

The efficiencies of InxGa1-xN two-junction solar cells are calculated with various bandgap combinations of subcells under AM1.5 global, AM1.5 direct and AM0 spectra. The influence of top-cell thickness on efficiency has been studied and the performance of InxGa1-xN cells for the maximum light concentration of various spectra has been evaluated. Under one-sun irradiance, the optimum efficiency is 35.1% for the AM1.5 global spectrum, with a bandgap combination of top/bottom cells as 1.74 eV/1.15 eV. And the limiting efficiency is 40.9% for the highest light concentration of the AM1.5 global spectrum, with the top/bottom cell bandgap as 1.72 eV/1.12 eV.

AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 2 inch sapphire substrates by MOCVD, and 0.8-µm gate length devices were fabricated and measured. It is shown by resistance mapping that the HEMT structures have an average sheet resistance of approximately 380 Θ/sq with a uniformity of more than 96%. The 1-mm gate width devices using the materials yielded a pulsed drain current of 784 mA/mm atV gs=0.5 V andV ds=7 V with an extrinsic transconductance of 200 mS/mm. A 20-GHz unity current gain cutoff frequency (f T) and a 28-GHz maximum oscillation frequency (f max) were obtained. The device with a 0.6-mm gate width yielded a total output power of 2.0 W/mm (power density of 3.33 W/mm) with 41% power added efficiency (PAE) at 4 GHz.