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The Rb/Sr ratio of lake sediments has been widely adopted as an indicator of weathering intensity in studies of past climate change, but the geochemical significance of this ratio varies with timescale. Here we present Rb/Sr data for the last 300 years for sediments collected from Chaonaqiu Lake in the Liupan Mountains of the western Chinese Loess Plateau as a decadal-scale record of weathering intensity. To validate the application of this weathering proxy, we correlated the record with those of other major elements, rock-forming minerals, and paleoclimatic proxies. We found that Rb/Sr ratios are influenced mainly by Sr activity within the lake catchment (where Sr is likely sourced from albite). In addition, higher (lower) Rb/Sr ratios of bulk sediments from Chaonaqiu Lake are correlated with lower (higher) fractions of terrigenous detritus (SiO2, Ti, K2O, Al2O3, and Na2O). Lake bulk sediment Rb/Sr ratios are dominated by the input of terrigenous detritus over decadal timescales. Our data show that physical and chemical weathering in Chaonaqiu Lake catchment have opposing influences on bulk sediment Rb/Sr ratios, competing to dominate these ratios of lake sediments over different timescales, with ratios reflecting the relative importance of the two types of weathering. We infer that the Rb/Sr ratios of Chaonaqiu Lake sediments reflect climatic signals of precipitation and temperature over long timescales and of precipitation over short timescales.

Development of stretchable wearable devices requires essential materials with high level of mechanical and electrical properties as well as scalability. Recently, silicone rubber-based elastic polymers with incorporated conductive fillers (metal particles, carbon nanomaterials, etc.) have been shown to the most promising materials for enabling both high electrical performance and stretchability, but the technology to make materials in scalable fabrication is still lacking. Here, we propose a facile method for fabricating a wearable device by directly coating essential electrical material on fabrics. The optimized material is implemented by the noncovalent association of multiwalled carbon nanotube (MWCNT), carbon black (CB), and silicon rubber (SR). The e-textile sensor has the highest gauge factor (GF) up to 34.38 when subjected to 40% strain for 5,000 cycles, without any degradation. In particular, the fabric sensor is fully operational even after being immersed in water for 10 days or stirred at room temperature for 8 hours. Our study provides a general platform for incorporating other stretchable elastic materials, enabling the future development of the smart clothing manufacturing.

The cultivation of students can not be separated from excellent teachers, Jiangxi rural areas should be underdeveloped economy, life is not perfect and other reasons, resulting in a shortage of excellent teachers. In this context, it is necessary to carry out pre-service education and training for general-practice teachers in rural primary schools. On the basis of analyzing the necessity of pre-service training, this paper fully investigates the present situation of teacher training in rural primary schools, so as to construct the feasible mechanism of pre-service training for general-practice teachers and contribute to the development of education in rural areas of Jiangxi Province.

This article starts a research on the development of intra-city clothing distribution under the O2O model. This article mainly analyzes the O2O model and the meaning, status quo and characteristics of intra-city delivery under this model. At the same time, it also focuses on the current situation, characteristics and existing problems of clothing intra-city distribution under the O2O model, combined with existing typical cases to conduct a more comprehensive analysis, and put forward a proposal for intra-city clothing distribution under the O2O model on this basis. Finally, this research focuses on the proposal of intra-city clothing distribution under the O2O model, and mainly develops a relatively new shopping mode and distribution environment from five aspects of supply side, sales side, distribution side, technology side, and service side; while conforming to the O2O trend, it will also achieve healthy economic development.

With the development of science and technology, the technology represented by the Internet and modern communication is gradually changing the whole society. The traditional trading methods and advanced Internet technology create a new way of transaction—electronic commerce transaction. While electronic commerce brings the efficiency and wealth to the human society, it also takes the effect on the tax implications. The e-commerce has raised a serious challenge to the current tax policy, tax system and international tax issues. In order to protect the financial interests, different countries demonstrate different attitudes and propose corresponding tax measures to adapt and improve the development of e-commerce. In China, electronic commerce has led to some serious problems, such as the difficulties in tax collection and management, and growing of the tax revenue loss. Currently, e-commerce guidance policy is staying on the macro-level. Without specific tax system, there will be inevitably results of the loss of state revenue and the block of fair competition between e-commerce and traditional transactions if our country does not introduce the reasonable e-commerce-related tax policies and measures. For the issue of China’s e-commerce taxation, this paper discusses the relationship between e-commerce and economic growth and tax revenue on the basis of foreign experience in tax policy, and puts forward tax policy advice of our country’s electronic commerce.

Insurance is a tool for diversifying risks and reducing losses, and is also a reasonable means for risk management under market economy conditions. In daily life, individuals and companies are also exposed to infringement or litigation risks when they exercise intellectual property rights. This will bring huge economic burdens to individuals or businesses. Currently, intellectual property infringement cases in China are on the rise every year. Intellectual property insurance is an insurance system established for the purpose of infringement of intellectual property rights, compensation for intellectual property litigation costs and damages. At present, intellectual property insurance is practiced in many countries. The author introduces foreign intellectual property insurance legal system such as United States, Britain and Japan, also the present situation of intellectual property insurance in China, especially a series of practices in intellectual property insurance field in China. Therefore, under this background, the studies and analyzes current situation of intellectual property insurance of these countries are necessary for China to establish a legal system, which will help China to form a protective system of intellectual property rights of legal relief, administrative arbitration and economic compensation, it has some advantages, it should be as an important part of China’s intellectual property strategy.

Randomized picking is a classical, high practical value, but complex mission for collaborative robots. In this paper we presents an efficient and robust perception system for this task, which is capable of detecting and classifying each instance in occlusion environment as well as outputting the 6D pose of target object for grasping. For system running efficiency, we design a grasping strategy which can automatically select appropriate target object among multiple ones, deal with the situation of object point cloud insufficient in amount of points and correct a particular wrong registration result that violate common sense. A gripper open degree estimation algorithm is also presented so as to prevent fingers colliding with neighbor objects of the target. Finally, to test the effectiveness and robustness of our proposed approaches, we show an experimental result of the whole robot system.

With the deepening of China's reform and opening up and the enlarging enrollment of higher education institutions, the status and role of higher education in our country are increasingly important. In the process of management, the higher education needs to follow more requirements and systems [1]. In this paper, we mainly discuss the issue of China's higher education from the perspective of the legal system. From the perspective of the rule of law, this paper analyzes the status quo of the system of governing the university according to law in colleges and universities, points out many problems existing in the construction of the system of managing the university according to law, and then proposes the feasible suggestions for solving the problems.

Objective To investigate risk factors for hepatitis B virus (HBV) intrauterine infection. Methods Peripheral blood samples and clinical data were collected from 174 pregnant women who were positive for hepatitis B surface antigen (HBsAg). Their 176 neonates received an active–passive immunization schedule at 0, 1, and 6 months. Blood samples from the infants, collected before immune prophylaxis administration, were tested for HBV markers and HBV DNA. Results The intrauterine infection rate at 6 months after birth was 5.1%. Maternal HBV DNA positivity (OR 11.362; 95% CI, 1.389–92.931), hepatitis B e antigen (HBeAg) positivity (OR 7.278; 95% CI, 1.734–30.538), and thalassemia minor (OR 15.619; 95% CI, 2.239–108.964) were associated with intrauterine infection. The intrauterine infection rate for mothers with 10 5 copies/mL of serum HBV DNA or more was 18.2%, compared with 0.8% for mothers with less than 10 5 copies/mL. Conclusion A positive HBsAg test at 24 hours and/or 1 month of age followed by a positive test at 6 months is an objective and comprehensive criterion for the diagnosis of HBV intrauterine infection. Maternal HBV DNA positivity (especially 10 5 copies/mL of HBV DNA or more), HBeAg positivity, and thalassemia minor are risk factors for HBV intrauterine infection.

A set of GaN films were overgrown by hydride vapor phase epitaxy (HVPE) on nanoporous GaN templates with different pore diameters. These samples have various properties as seen from the measurements of X-ray diffraction (XRD) and photoluminescence (PL). Cross-sectional observations under a scanning electron microscopy (SEM) reveal that the overgrowth mechanism and process are strongly related to the dimension of nanopores, indicating that an optimum diameter exists for the properties of subsequent HVPE–GaN layers. When the diameters of nanopores are less than the optimum value, the pores on top of GaN templates can be left, and the properties of HVPE–GaN films show significant improvement. In contrast, the pores are almost stuffed with HVPE–GaN films, which obviously limit the improvement degree of HVPE–GaN films.

The cytokinin biosynthesis gene, isopentenyl transferase (ipt), under the control of an 821 bp fragment of the LEACO1 gene promoter (from Lycopersicon esculentum) was introduced into Dendranthema x grandiflorium 'Iridon' (chrysanthemum). LEACO1(0.821kb)-ipt transgenic lines grown in the vegetative state, exhibited a range of phenotypic changes including increased branching and reduced internode lengths. LEACO1(0.821kb)-ipt transgenic lines grown in the generative state, exhibited increased flower bud count that ranged from 3.8- to 6.7-times the number produced by wild-type plants. Dramatic increases in flower number were associated with a delay of flower bud development and a decrease in flower bud diameter. RT-PCR analysis indicated differences in ipt gene expression between individual transgenic lines that exhibited a range of phenotypes. Within an individual transgenic line, RT-PCR analysis revealed changes in ipt gene expression at different stages of generative shoot development. Expression of ipt in transgenic lines correlated well with high concentrations of the sum total to bioactive cytokinins plus the glucosides and phosphate derivatives of these species, under both vegetative and generative growth conditions. In general, transgenic lines accumulated higher concentrations of both storage-form cytokinins (O-glucosides) and deactivated-form cytokinins (N-glucosides) in generative shoots of than in vegetative shoots. Based on the range of phenotypes observed in various transgenic chrysanthemum lines, we conclude that the LEACO1 (0.821kb) -ipt gene appears to have great potential for use in ornamental crop improvement.

Using n-on-p InGaAs/InAlAs/InP heterojunction structure with relative thin Be doped linearly graded InxAl1−xAs as buffer layer, wavelength extended InGaAs photodiodes with 50% cutoff wavelength of 2.0 μm and 2.4 μm at room temperature have been grown by using gas source MBE with a convenient but reliable correlative ramping procedure, and their dark current performance in a wide temperature range have been investigated. For 300 μm diameter detectors at 290 K, typical R0A and dark current at 10 mV reverse bias are 760 Ωcm2/11.3 nA for cutoff wavelength of 2.0 μm, and 104 Ω cm2/75.1 nA for cutoff wavelength of 2.4 μm. Room temperature peak detectivity D λ p ∗ reaches 1.3E11 cm Hz1/2/W and 6.5E10 cm Hz1/2/W, respectively measured using 900 K black body source. For back illumination the parameter optimization of n-on-p configuration is much easier than those of p-on-n, also the structure quality of the n-on-p is better than those of p-on-n because of the high Be doping in the linear graded buffer layer instead of Si.

An array of high-density, vertically aligned GaN nanowires is fabricated through thermal evaporation of GaN powder with the assistance of HCl gas. All GaN nanowires with needlelike tips are well-aligned with the axis direction perpendicular to the substrate without the use of catalysts. A possible growth mechanism of the vertical GaN nanowires array is proposed. Furthermore, field emission measurement shows that the obtained GaN nanowires array has a lower turn-on field of 2.1 V/μm, and the current density is about 1 mA/cm(2) at a bias field of 4.5 V/μm, which means such GaN nanowires are good candidates for large area and uniform flat display applications.

Using heterojunction structure with relative thin linearly graded In x Al 1− x As as buffer layer and In 0.8 Al 0.2 As as cap layer, wavelength extended In 0.8 Ga 0.2 As photodiodes with 50% cut-off wavelength of 2.42 μm at room temperature have been grown by using gas source MBE with a convenient but reliable procedure, and their performance over a wide temperature range have been extensively investigated. This structure with wider bandgap buffer and cap is suitable for both front and back illuminations. For those photodiodes with 500 μm mesa diameter, the typical dark current ( V R = 10 mV) and R 0 A are 160 nA/137 Ω cm 2 at 290 K, and 26.7 pA/1.08 MΩ cm 2 at 150 K, respectively for doping level of 1E17 cm −3 , at this higher doping level decrease in the response and appearance of unusual spectrum were also observed, which leaves a room for the careful optimization of the doping and structure.

We report on pulsed single-mode operation of mid-infrared distributed feedback quantum cascade lasers with a very low-threshold current density at room temperature. The lasers exploited a three-well vertical transition active region and a low-doped injector as the active layers. A novel waveguide and grating structure was proposed to achieve a sufficient coupling coefficient and low waveguide loss simultaneously. For the λ∼8.4 μm lasers, a low-threshold current density (J th ) of 1.78 kA/cm 2 and a peak output power (Pout) of 4mW are achieved at room temperature. For the λ∼7.7 μm lasers, J th is as low as 970 A/cm 2 at room temperature and the corresponding Pout reaches 75 mW. Both kinds of the lasers show single-mode emission with a high side-mode suppression ratio of ∼30dB.

A high-quality GaN film was (W-GaN) grown by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition (MOCVD) GaN templates with a tungsten (W) interlayer. A sample without interlayer was also grown at the same time for comparison. Significant reductions of dislocation density in W-GaN film is confirmed by the result of high-resolution X-ray diffraction and transmission electron microscope (TEM) observation. The improvement of optical properties of the W-GaN is confirmed by photoluminescence (PL) result. A shift of PL peak suggests that the strain is lower in the W-GaN than the film without W interlayer. This technique offers a potential path to obtain high-quality GaN film as free-standing substrate.

Thick GaN layer deposited by hydride vapor phase epitaxy (HVPE) on a metalorganic chemical vapor deposition (MOCVD) GaN template with a thin low temperature (LT) AIN intermediate layer was investigated. High resolution X-ray resolution diffraction (HRXRD) shows that the crystalline quality of thick GaN layer was improved compared with the template. As confirmed by atomic force microscopy (AFM) observations, the surface morphology of AIN intermediate layer helps to improve the nucleation of GaN epilayer. Photoluminescence (PL) spectra measurement shows its high optical quality and low compressive stress, and micro Raman measurement confirms the latter result. Thus, the deposition of the LT-AIN interlayer has promoted the growth of an HVPE-GaN layer with an excellent crystalline quality.

Using homo-junction structure and relative thin linear graded InxGa1−xAs as the buffer layer, extended wavelength InGaAs PIN photodetectors with cut-off wavelength of 2.2 and 2.5 μm at room temperature have been grown by using GSMBE, and their performance over a wide temperature range have been extensively investigated. For those 2.2 or 2.5 μm detectors with 100 μm diameter, the typical dark current (VR = 10 mV) and R0A are 57 nA/10.3 Ω cm2 or 67 nA/12.7 Ω cm2 at 290 K, and 84 pA/4.70 kΩ cm2 or 161 pA/3.12 kΩ cm2 at 210 K respectively. The thermal activation energies of the dark current are 0.447 eV or 0.404 eV for 2.2 or 2.5 μm detectors respectively.

Thick GaN films were deposited on sapphire substrate by hydride vapour phase epitaxy (HVPE) in two steps at 1050 °C. The substrate was first nitridated for different times between 1 and 10 minutes before deposition of a 12 pm thick layer. X-ray rocking curves show a minimum for 5 and 7 minutes of nitridation. The shift of the photoluminescence peak (PL) at room temperature from 3.328 to 3.405 eV is consistent with the evolution of the microstructure which is characterised by non-compact layers for the shortest times of nitridation. The nitridation of the sapphire surface results in the formation of a damaged layer with a thickness varying with the nitridation times. In this interfacial area, flat interfaces are present, but A1N nanocrystals may be observed as well as an amorphous zones containing Al, O and N.

The morphology of the top surface for HVPE GaN layers grown on a MOCVD GaN template with a thin LT-AlN interlayer was investigated. This surface is characterized by the formation of numerous hillocks associated with screw dislocations or nanopipes. Their size is large and may reach more than 1 mm. The rocking curves of the 002 and 102 reflections correspond to a relaxed layer. The HREM images of the as-deposited and annealed interlayers show a perfect atomic structure with a very abrupt AlN/HVPE GaN interface. Thus, the deposition of the LT-AlN layer has promoted the growth of an HVPE layer with an excellent crystalline quality.

Strained InAs 0.43 P 0.57 /InP and strain-compensated InAs 0.43 P 0.57 /In 0.7 Ga 0.3 As 0.43 P 0.57 multiple quantum well (MQW) structures were grown by gas source molecular beam epitaxy. The observations of up to 5 satellite-diffraction peaks from the high-resolution X-ray diffraction measurements demonstrate good crystalline quality for both structures. The temperature dependence of the 1e–1hh transition energies, the line width of photoluminescence (PL) spectra and emission efficiency η of the two quantum well structures are compared by low-temperature PL measurements. The temperature dependence of the 1e–1hh transitions of the two quantum well structures is similar to that of InAs 0.43 P 0.57 bulk material. The thermal activation energies obtained for strain-compensated MQW are larger than those obtained for the strained one. Consequently, the PL emission efficiency decays much slower for the strain-compensated MQW than that for the strained one when temperature increases, indicating the superior temperature stability of luminescent efficiency for the strain-compensated MQW. The obtained results can be used as references to the design and fabrication of optoelectronic devices.

A novel comprehensive two-dimensional (2-D) separation system coupling capillary high-performance liquid chromatography (cHPLC) with microchip electrophoresis (chip CE) is demonstrated. Reversed-phase cHPLC was used as the first dimension, and chip CE acted as the second dimension to perform fast sample transfers and separations. A valve-free gating interface was devised simply by inserting the outlet-end of LC column into the cross-channel on a specially designed chip. A home-made confocal laser-induced fluorescence detector was used to perform on-chip high-sensitive detection. The cHPLC effluents were continuously delivered to the chip and pinched injections of the effluents every 20 seconds were employed for chip CE separation. Gradient elution of cHPLC was carried out to obtain the high-efficiency separation. Free-zone electrophoresis was performed with triethylamine buffer to achieve high-speed separation and prevent sample adsorption. Such a simple-made comprehensive system was proved to be effective. The relative standard deviations for migration time and peak height of rhodamine B in 150 sample transfers were 3.2% and 9.8%, respectively. Peptides of the fluorescein isothiocyanate (FITC)-labeled tryptic digests of bovine serum albumin were fairly resolved and detected with this comprehensive 2-D system.

The two-dimensional growth and dislocation density of GaN epi-layer were studied by using single-buffer layer (SBL) and double-buffer layers (DBLs) grown on sapphire (0001) by radio frequency plasma assisted molecular beam epitaxy (RFP-MBE). The DBLs consist of two buffer layers deposited at two different temperatures T1 and T2 (T2>T1), and the high temperature annealing was performed after the buffer layer growth at T1. The surface morphology was observed by atomic force microscope (AFM), and the two-dimensional growth of GaN epi-layer was characterized by ω-scan rocking curve of X-ray diffraction (XRD). It was found that the rms (root-mean-square) roughness was decreased obviously and the full-width at half maximum (FWHM) of ω-scan rocking curve was reduced drastically when the GaN DBLs were used. The dislocation density of the GaN epi-layer grown on DBLs, which was estimated by two-dimensional triple axes mapping (TDTAM) of XRD measurement, was only a half as compared with that grown on SBL. It was shown that the quality of GaN epi-layer was improved by using DBLs.

Extended balance equations accounting for the conduction–valence interband impact ionization (II) process in semiconductor heterostructures are presented. The II effect and terahertz (THz) field influence on electron transport in InAs/AlSb heterostructures is studied. It is shown that the II process usually results in a decrease in electron velocity and temperature when compared to the case without the II process. Qualitative agreement is obtained between the calculated electron–hole generation rates and available experimental data. Comparison with published experimental data on THz-driven heterostructures is also made.

Anatase titania nanoparticles are prepared using pyrolysis of titanium tetrabutoxide in oxygen free and oxygen containing atmospheres by MOCVD method. Influence of oxygen on the properties of the titania nanoparticles is investigated, followed by discussion. The results show that oxygen influences not only the particle size but also the particle size distribution of the nanoparticles. With increasing oxygen flow rates, the average grain sizes of the nanoparticles decrease and the particle size distributions become uniform. Oxygen exerts great influence on the nucleation rate of the nanoparticles and reaction kinetics occurred in the reactor. The formation of titania nanaoparticles by MOCVD is not a growth controlled process, but is a nucleation rate controlled process.

The behavior of Si in GaN has been investigated in the wide doping range from 1×1017 to 9×1019 cm−3 by photoluminescence (PL). PL studies at 77 K for doped specimens show that the intensity of the near-band-edge emission increased monotonically as the Si concentration increases. The intensity of the yellow luminescence (YL), however, remains almost constant, which indicates that Si does not strongly influence the density of deep centers in GaN. The red-shift of the near-band-edge emission due to increase the Si concentration shows that bandgap renormalization (BGR) effect is much more important than the Burstein–Moss (B-M) effect in Si-doped GaN. With Si doping as high as 9×1019 cm−3, a new peak due to donor-to-acceptor recombination appears in the PL spectrum. This donor-to-acceptor emission peak can also be observed in the PL spectrum of Si-doped GaN after thermal annealing. We attributed the appearance of the new acceptor level to the formation of SiN. A model has been proposed to illustrate the Si behavior in GaN in a wide range of Si concentrations.

Anatase titania nanoparticles with the average grain sizes ranging from 7.4 to 15.2 nm are prepared using pyrolysis of titanium tetrabutoxide in oxygen containing atmosphere by MOCVD method. Influence of preparation temperature on the average grain size of the particles is investigated, followed by discussion. At low preparation temperatures nucleation dominates the process while growth of the particles becomes a controlling factor at high temperatures. The as prepared anatase titania nanoparticles show a surface area as high as 180 m2 g−1. The transformation temperature of the high surface area nanoparticles from anatase to rutile is as high as 700–1000 °C, which is about 200 °C higher than that of the particles prepared by spray hydrolysis method.

Schottky barriers are used extensively in high frequency switching, mixing and rectifying circuit for their good DC and RF characteristics. In this paper we report that devices measured in a double-balance mixer circuit show that the typical value of the DBS noise figure of the mixer diode is 6.1 dB at 89.5 GHz. Very good results were also observed in the 12.5, 8, 5 and 4 mm bands. However, the barrier height is virtually constant and the operation stability depends strongly on the metallurgy of the Schottky contact. In addition, properties of planar doped barrier (PDB) diodes with an n+/i/p+/i/n+ configuration grown by molecular beam epitaxy (MBE) with precise control of the barrier height, were also studied. The results of artificial tailored I–V characteristics, junction capacitance and the detector application are also presented.

Si-doped GaN with a carrier concentration of 6×10 17 cm −3 was grown on c-plane sapphire substrates by molecular beam epitaxy (MBE) equipped with a nitrogen RF plasma source. The thermal annealing process was performed in a nitrogen atmosphere with a tungsten–halogen lamp as the thermal source. Double crystal X-ray diffraction (DCXRD) and 77 K photoluminescence (PL) have been employed to investigate the effects of thermal annealing on Si-doped GaN films. Both annealing temperature and annealing time have been varied to investigate the influence of different annealing processes on the sample. The DCXRD results show that the dislocation density in the sample decreases after thermal annealing. 77 K PL of GaN annealed longer than 300 s at 950°C shows a new peak at 378 nm. The integrated intensity of the peak increases dramatically with increasing annealing time. The excitation power dependence of the 378 nm peak indicates that the emission was associated with donor-acceptor pair (DAP) transitions, and a similar peak has been observed in highly Si-doped GaN with a carrier concentration of 9×10 19 cm −3 . We attribute the acceptor in DAP to Si N .

The high density vertically aligned GaN nanorods array was fabricated by thermal evaporation of GaN powder with the assistance of HCl gas. The GaN nanorods array was used as template for GaN film growth by hydride vapor phase epitaxy (HVPE). The full width at half maximum values (FWHM) of high-resolution X-ray diffraction (HRXRD) rocking curves for the GaN film with GaN nanorods array template are 247 arc sec (002 reflection) and 308 arc sec (102 reflection), while those for the GaN film without GaN nanorods array template are 292 and 369 arc sec, respectively. This result indicates a significant reduction of dislocation density in the overgrown GaN film with GaN nanorods array template. Photoluminescence spectra measurements reveal the compressive strain relaxation and an improvement in the quality of the overgrown GaN film with GaN nanorods array template as compared to the regrown GaN film without GaN nanorods array template, which is consistent with the trend observed by HRXRD.

Al0.2Ga0.8As0.02Sb0.98/In0.24Ga0.76As0.05Sb0.95 strained quantum well structures were successfully grown by solid source molecular beam epitaxy. X-Ray rocking curves and reciprocal space mapping were applied to determine the strain status of epilayers. Photoluminescence was used to investigate band alignment of AlGaAsSb/InGaAsSb quantum wells. For samples with low Al concentration barrier, type II band alignment was found in such structures. The optical transition is between bound state in conduction band and continuous state in valence band. If the Al concentration in AlGaAsSb barrier increases, the band alignment changes to type I. The optical transition is between bound states. Due to the 0.5% lattice mismatch between AlGaAsSb layer and GaSb substrate, a thick barrier will lead to relaxation, and this has been proven by PL measurements.

InP epitaxial layers and InGaAs/InAlAs/InP modulation doped heterostructures were grown by gas source molecular beam epitaxy, in which arsenic and phosphorus beams were obtained by thermal cracking of AsH3 and PH3. High purity InP layers have been obtained by optimizing growth parameters. To identify the species of impurity and defect in high quality InP layers, low temperature photoluminescence (PL) and photothermal ionization spectroscopy measurements were carried out. The residual donors were determined to be silicon and sulfur. To obtain a deep insight to the electronic subband structure of the two-dimensional electron gas (2DEG) system, Shubnikov-de Haas, quantum Hall effect measurements and field-dependent cyclotron resonance measurements were conducted. The electron density on each subband in 2DEG was determined to be 2.84×1012 and 3.4×1011 cm−2, respectively. The effective masses of the two subbands are (0.061±0.001)m0 for the zero subband and (0.049±0.001)m0 for the first subband. An optoelectronic integrated circuit (OEIC) structure consisting of high electron mobility transistor (HEMT) and metal semiconductor metal photo detector (MSM-PD) was achieved by gas source molecular beam epitaxy with one growth run. The responsibility of MSM-PD is 0.5A/W. DC transconductance of an InGaAs/InAlAs HEMT with 1.5-μm gate length is 305 mS mm−1; the maximum saturation current is 350 mA mm−1 and the pinch-off voltage is −1.4 V. The gain of the HEMT amplifier is 14 dB. The integrated photoreceiver could successfully operate at a data rate of 622 Mbit s−1.

GaN (Gallium nitride) has been grown successfully on sapphire by RF plasma MBE through optimizing the growth condition. Two dimensional triple axis mapping (TDTAM) was used to characterize the GaN epilayers. The dislocation density in the epilayers was estimated to be about 7.8×108 cm−2 according to the mosaic model. The 77K photoluminescence (PL) of the Si-doped GaN with different concentration show that Si can act both donor and acceptor at very high concentration. Transmission spectrum has also been measured for further understanding of the sample.

The excitonic emissions near band edge, the donor-to-acceptor pair (DAP) emissions and the yellow luminescence (YL) in undoped GaN and As-doped GaN at a low doping level have been investigated. At 4.2 K, the intensity of the DAP emissions around 3.28 eV were observed to increase when the As concentration is increased. This enhancement has been correlated with an increase of the As-related isoelectronic centers. On the other hand, a remarkable reduction of the yellow luminescence due to the incorporation of As into GaN is found at 4.2 K, and it persists up to room temperature where the DAP signal has got quenched due to thermal ionization. These results suggest that the suppression of the YL is due to the passivation of the YL deep centers by the As-incorporation.

The overall photoluminescence properties of In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As single quantum well and multiple quantum wells of the same InGaAs well width 4.0 nm are reported. Results show that the dominant recombination processes in the two structures are radiative recombination in the whole measuring temperature range from the photoluminescence intensity–excitation power dependence, but the recombination process in the single quantum well structure is somewhat like band-to-band type. The band gap–temperature dependence relationship, photoluminescence peak's full width at half maximum–temperature dependent relationship and the photoluminescence spectra line shape at low temperature are in favor of the gradual evolution from excitonic to band-to-band type in the single quantum well structure.

GaN epilayers of about 1 μm thick were grown directly on 6H–SiC(0 0 0 1)substrates by direct current plasma assisted molecular beam epitaxy. High-resolution X-ray diffraction and two-dimensional triple axis mapping were used to characterize the GaN epilayers. A FWHM of 11.9 arcmin for an ω scan and 1.2 arcmin for an ω /2 θ scan were observed. A careful study of the rocking curves showed that there were some large mosaics in the GaN epilayers. The two dimensional triple axis mapping showed that the GaN mosaics were disoriented in the (0 0 0 1) plane but rather uniformed in the direction perpendicular to the plane. A mosaic model was deduced to explain the phenomenon, and the dislocation density was estimated to be about 2×10 9 cm −2 according to the model.

Many different reflections have been investigated by high resolution x-ray diffraction on gas source molecular beam epitaxy grown strained InGaAs/InAlAs/InP heterostructures to study the Bragg peak widths. Results show that even deducting the influence of the intrinsic peak width and the influence of the instrument broadening, for either InGaAs or InAlAs epilayers, a linear relationship between the square of the Bragg peak width and tan2 θB exists with θB the Bragg angle, for either grazing incidence or grazing emergence geometry. Different slopes for the linear relationship have been measured in the two different geometries. Systematically, a much bigger peak width is detected under a grazing incidence geometry than that under a grazing emergence geometry for the same asymmetric reflection. The phenomenon is explained by the existence of a normal strain gradient along the growth direction of the epilayer’s thickness. This normal strain gradient has been confirmed by x-ray triple-axis two-dimensional mapp...