Search

Ultrafast dynamics of spin relaxation in monolayer WSe2 and the WSe2/graphene heterojunction investigated using a circularly polarized femtosecond pump–probe system.

In order to explore the efficient investigate and utilization of emulsion produced by enzyme-assisted aqueous extraction of walnut oil, the effects of different enzyme treatment (including Alcalase 2.4L, Ban 480L α-amylase, Neutrase 0.8L, Pectinex SP-L, Celluclast 1.5L) on the characteristics of emulsion were studied to characterize its emulsifying characteristics The emulsion composition, particle size distribution, Zeta potential, rheological properties and protein surface hydrophobicity of emulsion were determined to characterize its emulsifying properties. The results showed that the particle size of the emulsion obtained from enzymatic hydrolysis showed a smaller trend and the absolute value of Zeta potential showed a larger trend in the presence of enzymes. On emulsion protein, hydrophobicity of emulsion protein was obtained by hydrolysis with different enzymes showed that the trend followed the order: Celluclast 1.5L> Ban 480L >Neutrase 0.8L >Pectinex SP-L >control> Alcalase 2.4L. The particle size, zeta potential, ability to increase emulsion viscosity and interfacial hydrophobicity of emulsion proteins affected the emulsion physical stability and the effect of demulsification. The results of rheological analysis show that emulsions from Ban 480L α-amylase, Neutrase 0.8L and Celluclast 1.5L hydrolysate still maintained their elastic structure damaged by shear rate and were more stable, and the emulsions obtained by Alcalase 2.4L and Pectinex SP-L were unstable which was easy to be broken.

The appearance of van der Waals heterostructures offers a new solution to valleytronics. Here, we observe the spin-valley depolarization process of electrons and holes in type-II MoS

Strain is one of the effective ways to modulate the band structure of monolayer transition metal dichalcogenides (TMDCs), which has been reported in theoretical and steady-state spectroscopic studies. However, the strain effects on the charge transfer processes in TMDC heterostructures have not been experimentally addressed thus far. Here, we systematically investigate the strain-mediated transient spectral evolutions corresponding to excitons at band-edge and higher energy states for monolayer MoS2 and monolayer WSe2. It is demonstrated that Γ and K valleys in monolayer WSe2 and monolayer MoS2 present different strain responses, according to the broadband femtosecond pump-probe experimental results. It is further observed that the resulting band offset changes tuned by applied tensile strains in MoS2-WSe2 heterostructures would not affect the band-edge electron transfer profiles, where only monolayer WSe2 is excited. From a flexible optoelectronic applications perspective, the robust charge transfer under strain engineering in TMDC heterostructures is very advantageous.

Monolayer transition metal dichalcogenide quantum dots (TMDC QDs) could exhibit unique photophysical properties, because of both lateral quantum confinement effect and edge effect. However, there is little fundamental study on the quantum-confined exciton dynamics in monolayer TMDC QDs, to date. Here, by selective excitations of monolayer WS2 QDs in broadband transient absorption (TA) spectroscopy experiments, the excitation-wavelength-dependent ground state bleaching signals corresponding to the quantum-confined exciton states are directly observed. Compared to the time-resolved photophysical properties of WS2 nanosheets, the selected monolayer WS2 QDs only show one ground state bleaching peak with larger initial values for the linear polarization anisotropy of band-edge excitons, probably due to the expired spin–orbit coupling. This suggests a complete change of the band structure for monolayer WS2 QDs. In the femtosecond time-resolved circular polarization anisotropy experiments, a valley depolarization time of ∼100 fs is observed for WS2 nanosheets at room temperature, which is not observed for monolayer WS2 QDs. Our findings suggest a strong state-mixing of band-edge valley excitons responsible for the large linear polarization in monolayer WS2 QDs, which could be helpful for understanding the exciton relaxation mechanisms in colloidal monolayer TMDC QDs.

Understanding and controlling the charge transfer processes of two-dimensional (2D) materials are fundamental for the optimized device performance based on 2D semiconductors and heterostructures. The charge transfer rate is very robust in transition metal disulfide (TMD) heterostructures with type II band alignments, which can be manipulated by intercalating a dielectric layer like hBN to isolate the donor and acceptor monolayers. This study shows that there is an alternative way to change the electron transfer and recombination rates in the case of nLMoS2/mLWSe2 multilayer heterostructures, where the donor-acceptor distance is maintained, but the rate of electron transfer is strongly layer dependent and shows asymmetry for the layer number of donor and acceptor monolayers. Especially, the 1LMoS2/2LWSe2 heterostructure slows electron transfer and charge recombination rates ∼2.3 and ∼12 times that of the 1LMoS2/1LWSe2 heterostructure, respectively, which have been competitive with that in the 1LMoS2/hBN/1LWSe2 heterostructure. From an application perspective, the noninterfacial electron transfer in which photogenerated electrons should across more than one atomically thin layer is not favorable due to the built-in electric field established by the initial interfacial electron transfer.

Monolayer transition metal dichalcogenide quantum dots (TMDC QDs) could exhibit unique photophysical properties, because of both lateral quantum confinement effect and edge effect. However, there is little fundamental study on the quantum-confined exciton dynamics in monolayer TMDC QDs, to date. Here, by selective excitations of monolayer WS

Strain is one of the effective ways to modulate the band structure of monolayer transition metal dichalcogenides (TMDCs), which has been reported in theoretical and steady-state spectroscopic studies. However, the strain effects on the charge transfer processes in TMDC heterostructures have not been experimentally addressed thus far. Here, we systematically investigate the strain-mediated transient spectral evolutions corresponding to excitons at band-edge and higher energy states for monolayer MoS

The static and dynamic electrical characteristics of GaN-based blue light-emitting diodes with different numbers of quantum wells were investigated by software Silvaco technology computer-aided design numerically, which were essential for visible light communication study. As a factor impacts on the response time of light-emitting diodes, the capacitance, varying with applied bias, with modulation frequency, and with the numbers of quantum wells, was analyzed detailedly. Besides that, the response time of light-emitting diodes, including the optical rise time and fall time, was also firstly simulated in Silvaco, and then, based on these, the pure − 3 dB bandwidth of the light-emitting diodes without building-out circuit could be calculated, so as to self-design semiconductor devices like light-emitting diodes mentioned in this study with the optimum bandwidth used for visible light communication.

Licorice is a medicinal herb widely used to treat inflammation-related diseases in China. Isoliquiritigenin (ISL) is an important constituent of licorice and possesses multiple bioactivities. In this study, we examined the selective anti-AML (acute myeloid leukemia) property of ISL via targeting FMS-like tyrosine kinase-3 (FLT3), a certified valid target for treating AML. In vitro, ISL potently inhibited FLT3 kinase, with an IC50 value of 115.1 ± 4.2 nM, and selectively inhibited the proliferation of FLT3-internal tandem duplication (FLT3-ITD) or FLT3-ITD/F691L mutant AML cells. Moreover, it showed very weak activity toward other tested cell lines or kinases. Western blot immunoassay revealed that ISL significantly inhibited the activation of FLT3/Erk1/2/signal transducer and activator of transcription 5 (STAT5) signal in AML cells. Meanwhile, a molecular docking study indicated that ISL could stably form aromatic interactions and hydrogen bonds within the kinase domain of FLT3. In vivo, oral administration of ISL significantly inhibited the MV4-11 flank tumor growth and prolonged survival in the bone marrow transplant model via decreasing the expression of Ki67 and inducing apoptosis. Taken together, the present study identified a novel function of ISL as a selective FLT3 inhibitor. ISL could also be a potential natural bioactive compound for treating AML with FLT3-ITD or FLT3-ITD/F691L mutations. Thus, ISL and licorice might possess potential therapeutic effects for treating AML, providing a new strategy for anti-AML.

A novel package structure has been developed to fabricate quantum-dot (QD) white light-emitting diodes (WLEDs) by dispersing QDs into the backlight lens and integrating them with blue light-emitting diode to form white light. For this in-lens encapsulation structure, the luminous efficiency and lifetime of QD-WLEDs can reach 90 lm/W and 1000 h, which is 25 times longer than that of QD-WLEDs with on-chip encapsulation structure. Furthermore, a 32-inch prototype liquid crystal display TV shows a wide color gamut of 108% under the National Television Systems Committee standard with this in-lens encapsulation structure. The improvement performance should be attributed to providing a hermetic encapsulation environment preventing oxygen and water from reacting with the QDs and reducing the temperature of QDs due to in-lens package structure. Our results demonstrate that the in-lens solution can be a promising application in display backlight.

Understanding and controlling the charge transfer processes of two-dimensional (2D) materials are fundamental for the optimized device performance based on 2D semiconductors and heterostructures. The charge transfer rate is very robust in transition metal disulfide (TMD) heterostructures with type II band alignments, which can be manipulated by intercalating a dielectric layer like hBN to isolate the donor and acceptor monolayers. This study shows that there is an alternative way to change the electron transfer and recombination rates in the case of nLMoS

Three kinds of InGaN/GaN multiple-quantum-well light-emitting diode with different electron-blocking layers (EBLs) have been investigated numerically. The energy band diagrams, light–current curves, voltage–current curves, electrostatic fields, carrier concentrations in the quantum wells, electron current densities, radiative recombination rates in active region, and internal quantum efficiency (IQE) are reported. The results show that, when the conventional AlGaN EBL is replaced by a p-AlGaN/InGaN superlattice EBL or graded p-AlyGa1−yN/InxGa1−xN superlattice EBL, respectively, the light output power at 200 mA can be increased by 46.0% and 52.8%, the turn-on voltage can be decreased from 3.2 V to 3.0 V, the IQE can be increased by 45.6% and 53.8% at 200 mA, and the efficiency droop can be reduced from 31.2% to 21.6%. These improvements are mainly attributed to the properly modified energy band structures which favor carrier injection.

In this study, the structure, morphology, electrical and optical properties of Si and Ta co-doped gallium oxide (Ga2O3) films deposited on (1 0 0) Ga2O3, (0 0 0 1) sapphire and quartz substrates by pulsed laser deposition are analyzed. The Si and Ta co-doped Ga2O3 film on Ga2O3 substrate possessed the best crystal quality with a high carrier concentration of 1.12 × 1020 cm−3 and a conductivity of 2.13 S·cm−1 compared to the sapphire and quartz substrates. The Si and Ta co-doped Ga2O3 films on different substrates exhibited high transmittance (>73%) above 300 nm and smooth film surface. The optical gap of Si and Ta co-doped Ga2O3 films on Ga2O3, sapphire and quartz substrates decreases from 4.89 to 4.85 eV, and the corresponding Urbach energy increases from 0.396 to 0.704 eV, so the homoepitaxial Si and Ta co-doped Ga2O3 film possess the best quality.

In this work, segmented silver nanowires (AgNWs) with an average diameter of 60 nm have been successfully synthesized by a typical polyol method without any templates and seeds. The synthesized segmented AgNWs were strongly dependent on the reaction temperature and time. It was found from high-resolution transmission electron microscopy and selected area electron diffraction measurements that the connection node of segmented AgNWs was in the form of a twinned crystal. We speculated that these segmented AgNWs were possibly derived from end-to-end self-connection and self-concrescence of two neighbouring Ag nanorods or nanowires at a suitable reaction temperature and time, which is further confirmed by the secondary growth of AgNWs. In addition, segmented AgNWs were blended into hole transporting layers to enhance the performance of polymer solar cells (PSCs) by utilizing their localized surface plasmon resonance and optical scattering effects. As a result, the power conversion efficiency (PCE) and short-circuit current density (Jsc) of PSCs with segmented AgNWs increased from 2.81% and 8.99 mA cm−2 to 3.30% and 9.95 mA cm−2, respectively.

In this study, a new design of quantum barriers has been investigated numerically with the purpose of improving the optical performance of blue InGaN light-emitting diodes (LEDs). Through analysis of energy band diagrams, carrier concentrations, carrier current densities, Auger recombination rates, and radiative recombination rates, we obtain simulation results showing that the proposed structure with a mix of AlGaN and InGaN quantum barriers can significantly improve the light output power and internal quantum efficiency (IQE), being mainly attributed to successful enhancement of the hole injection efficiency and suppression of the electron leakage current. Moreover, the efficiency droop of the LEDs is markedly improved by using the newly designed structure.

In this study, three kinds of electron-blocking layer (EBL) in blue InGaN light-emitting diodes (LEDs) are investigated numerically. They are conventional AlGaN EBL, AlInGaN EBL and gradual Al and In composition p-AlInGaN EBL. Through the analysis of the output power, internal quantum efficiency, turn-on voltage, energy band diagrams, carrier current densities and radiative recombination rates, we have got the simulation results that the LED with gradual Al and In composition p-AlInGaN EBL exhibits a higher output power, a lower electron leakage, a better hole injection efficiency and a more peaceable efficiency droop than the LED with a conventional AlGaN EBL or with a AlInGaN EBL.

This paper introduces the basic principle of Viterbi code in OFDM system and a new implementation method based on FPGA, on and timing circuit are validated by using of EDA tools Quartus II. The new method is that the Viterbi decoding module is improved,which makes the design of the whole decoding structure can be improved and solves the compatibility problem among the modules. Finally, the simulation results is given and demonstrates that a good Viterbi code can be achieved by using FPGA in OFDM system, which can save the cost, shorten the designing cycle , and is convenient to speed up the listing of products, occupy less hardware resources, and comply with the development trend of modern communication.

In this study, a new design on last quantum barrier (LQB) is investigated numerically with the purpose of improving the optical performance of InGaN light-emitting diodes (LEDs). Through the analysis of the energy band diagrams, electrostatic fields, carrier concentrations, carrier current densities, and radiative recombination rates, we have got the simulation results that the proposed undoped-InGaN/AlInGaN superlattice (SL) LQB can significantly improve the output power and internal quantum efficiency, which is mainly attributed to the successful improvement in hole injection efficiency and suppression of electron current leakage. Moreover, the efficiency droop of the LEDs is improved slightly by using u-InGaN/AlInGaN SL as last barrier.

This paper introduces the basic principle of RS codes in OFDM system and the design method of 16 shift registers, finite field multiplicators and adders, on and timing circuit are validated by using of EDA tools Quartus II. Finally, the simulation results is given and demonstrates that a good channel encoding and decoding can be achieved by using FPGA in OFDM system, which can save the cost, shorten the designing cycle , and is convenient to speed up the listing of products, occupy less hardware resources, and comply with the development trend of modern communication.

Today's wireless communication has become the primary means of communication, the wireless communication relative to wired communications, its random parameter channel delay problem and fading problem raising a new challenge to the reliability of communication. This article describes the basic principle of OFDM system with interleaving and de-interleaving, Verification platform to build on this basis, and using EDA tools Quartus II functional and timing verify the correctness, Giving the integrated circuit simulation results, also showing the use of FPGA to achieve interleave and interleaving process well in OFDM systems. Effectively improve the reliability of the system, not only meet the needs of Systems on flexibility and real-time, but also occupy less hardware resources, fast, and consistent with the development trend of modern communications.

The characteristics of InGaN-based blue light-emitting diodes (LEDs) with an AlGaN/GaN superlattice (SL) electron-blocking layer (EBL) of gradual Al molar fraction below the active region are analyzed numerically. The output power, internal quantum efficiency, electrostatic fields, energy band diagrams, carrier concentrations, radiative recombination, and electron leakage current are investigated. The results indicate that the LED with n-type AlGaN/GaN SL EBL of gradual Al molar fraction has smaller electrostatic fields and lower electron leakage in its active region than the LED with a rectangular p-AlGaN EBL or n-AlGaN EBL. These result in a markedly reduced efficiency droop.

To make data bandwidth changeable and suit for different communication situations, thereby improving the utilization rate of hardware, this paper designed a direct sequence spread spectrum module with variable bandwidth and could used in a variety of occasions based on m sequence code generator with configurable series. The programmable m sequence code generator create a number of different pseudorandom sequence using FPGA programmable features and do XOR operation with signals waiting transmit. There for, it can achieve the purpose of spread spectrum. As the series can be changed, this module could fit normal communication, communication experiment, or other communication area which need high security level.

The advantages of GaN based light-emitting diodes (LEDs) with strain-compensated p-AlGaN/InGaN superlattice (SL) last quantum barrier (LQB) are investigated numerically. The simulation results indicate that the output power and internal quantum efficiency have been improved significantly by replacing the last barrier of the conventional u-GaN and p-GaN with p-AlGaN/InGaN SL. These improvements are mainly attributed to the improvement of electron confinement and hole injection efficiency caused by mitigating the polarization-induced band bending of last barrier with the new designed structure. Moreover, the efficiency droop of the LEDs is markedly improved by using p-AlGaN/InGaN SL as last barrier.

With the purpose to increase the uniformity of carrier distribution without sacrificing the enhancement of carrier injection efficiency, the light-emitting diodes (LEDs) without an electron-blocking layer (EBL) by using AlGaN step-like barriers (SLBs) is proposed and investigated numerically. The simulation results show that the enhanced electron confinement and hole injection efficiency are mainly attributed to the mitigated downward band bending induced by polarization field at the interface of the last barrier and EBL and the increased carrier distribution uniformity is due to step-like potential height for carrier of the new designed LEDs. In addition, the distribution of radiative recombination rate and the efficiency droop are markedly improved when the conventional GaN barriers are replaced by AlGaN SLBs and the EBL is removed.

The characteristics of blue InGaN light-emitting diodes (LEDs) with InGaN barriers and dip-shaped last barrier are investigated numerically. The simulation results show that the newly designed LEDs have a better performance over the conventional InGaN/GaN and InGaN/InGaN counterparts attributed to the enhancement of carriers confinement induced by the improved potential barrier height for electrons and holes, and the amelioration of electron-hole spatial overlap caused by the reduced polarization effect between the well and barrier. In addition, the efficiency droop and the radiative recombination rate are markedly improved by employing the LEDs with InGaN barriers and dip-shaped last barrier.

Now in general use in solar water heater, there is a long pipeline between water heater and tap, we have to empty the stored cold water before we use the hot water; and usually the water cannot meet required temperature due to the heating delay effect, thus the water also should be emptied, which leads to a waste of water resources. In order to solve this water wastage, we propose a device which can help to control the temperature and backflow of the water in water heater. The device accomplishes backflow of cold water automatically under the effect of gravity, and refluxed water will be stored in the recycle-water tank, thus ensuring the result that the water temperature satisfies the requirement. After the recycle-water tank is full, it will trigger the buoy to control the relay switch, then the water pump start to work to force the water into the water heater tank. Thus, realizing the recycling of water. This device can significantly save water resources in domestic water, and it has a broad market prospect.

The blue InGaN light-emitting diodes (LEDs), employing a lattice-compensated p-AlGaN/InGaN superlattice (SL) interlayer to link the last quantum barrier and electron blocking layer (EBL), are proposed and investigated numerically. The simulation results indicate that the newly designed LEDs have better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region over the conventional LEDs mainly attributed to the mitigated polarization-induced downward band bending. Furthermore, the markedly improved output power and efficiency droop are also suggested when the conventional LEDs corresponding to experiment data are replaced by the newly designed LEDs.

Based on spin-polarized density function theory, Electronic structure and magnetism of V-doped AlN are investigated. 6.25% V-doped AlN is found half-metallic with 100% carrier spin polarization of the conduction carriers. Per supercell has a net magnetic moment of 2 μ B , which are mostly localized within the VN 4 tetrahedron. V-doped AlN favors ferromagnetic ground state which can be explained by double exchange mechanism. To study the effects of electron correlation, GGA+ U calculations have been performed. Besides, formation energy is good for V doping. Our results suggest that the V-doped AlN may present a promising material and has potential applications in semiconductor spintronics devices.

In this study, the blue InGaN LEDs, employing gradual wide wells and thin barriers, is proposed. The carrier distribution, hole injection efficiency, electron leakage, radiative recombination rates, and Auger recombination rates are investigated numerically. The simulation results show that the newly designed LEDs have better performance over its conventional counterpart due to the successful enhancement of hole injection efficiency and suppression of Auger recombination. The simulation results also suggest that under relatively high current injection, the internal quantum efficiency (IQE), efficiency droop and light output power are markedly improved.

In this work, GaN-based light-emitting diodes (LEDs) with a p-GaN/i-InGaN short-period superlattice (SPSL) structure, p-GaN and undoped GaN last quantum barrier (LQB) have been numerically investigated by using the APSYS simulation software. It has been found that the efficiency droop is significantly improved when the undoped GaN LQB in a typical blue LED is replaced by a p-GaN/i-InGaN SPSL structure. According to the simulation analysis, using the p-GaN/i-InGaN SPSL structure as LQB is beneficial to increasing the hole injection efficiency and decreasing the electron current leakage. Therefore, the radiative recombination and optical power are enhanced.

C mono-doped and C–In co-doped ZnO are investigated by the first-principles calculations. It is found that the C mono-doped ZnO is p-type with hole carriers locating nearby valence band maximum. Furthermore, a shallower C acceptor energy level appears in the band gap after incorporating In into C-doped ZnO system. Meantime, compared with C mono-doped ZnO, C–In co-doped ZnO has a lower formation energy, correspondingly a higher chemical stability, and thus to enhance the incorporation efficiency of C. These results suggest that C–In co-doping method provided an efficient technique for realizing p-type ZnO.

Using the first-principles method based on the density functional theory, we have studied magnetic and optical properties of V-doped GaN. For 12.5% V-doped GaN, total energy calculations show that the ferromagnetic state is 255 meV lower than the antiferromagnetic state and is thus predicted to be the ground state with a Curie temperature above room temperature. The magnetic moments are localized at the V atoms and ferromagnetic exchange interaction is short ranged. The analysis of optical properties shows that V-doped GaN is a promising dielectric material and has potential applications in optoelectronic devices.

Using the first-principles method based on the density functional theory, we study electronic and magnetic properties of GaN doped with 6.25% of V. The V dopants are found spin polarized and order ferromagnetically in GaN, with a magnetic moment of 2 μ B per supercell. The V-doped GaN favors ferromagnetic ground state which can be explained in terms of double-exchange mechanism, and a Curie temperature above room temperature can be expected. Also, incorporation of V is easy. These results suggest that the V-doped GaN may present a promising dilute magnetic semiconductor and find applications in the field of spintronics.

Designs of p-doped in quantum well (QW) barriers and specific number of vertically stacked QWs are proposed to improve the optical performance of GaN-based dual-wavelength light-emitting diodes (LEDs). Emission spectra, carrier concentration, electron current density, and internal quantum e±ciency (IQE) are studied numerically. Simulation results show that the e±ciency droop and the spectrum intensity at the large current injection are improved markedly by using the proposed design. Compared with the conventional LEDs, the uniform spectrum intensity of dual-wavelength luminescence is realized when a specific number of vertically stacked QWs is adopted. Suppression of electron leakage current and the promotion of hole injection e±ciency could be one of the main reasons for these improvements.

The performance of GaN based devices could possibly be improved by utilizing the good p-type properties of GaP layer and it provides the possibility of the integration of InAlGaN and AlGaInP materials to produce new devices, if high quality GaP compounds can be grown on III-nitride compounds. In this paper, the growth of GaP layers on GaN by metalorganic chemical vapor deposition (MOCVD) has been investigated. The results show that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature GaP growth. Using a 40 nm thick GaP buffer layer, a single crystal GaP layer, whose full-width at half-maximum of the (1 1 1) plane measured by double crystal X-ray diffraction is 580″, can be grown on GaN. The V/III ratio plays an important role in the GaP layer growth and an appropriate V/III ratio can improve the quality of GaP layer. The GaP:Mg layer with hole carrier concentration of 4.2 × 10 18 cm −3 has been obtained.

An InGaN/GaN blue-violet light-emitting diode (LED) structure and an InGaN/GaN blue LED structure were grown sequentially on the same sapphire substrate by metal-organic chemical vapor deposition (MOCVD). At the low injection current, the intensity ratio of blue-violet light to blue light was almost constant, while the blue light intensity increased gradually with increasing injection current when the latter was more than 40 mA. High color rendering has been realized for a Y3Al5O12:Ce3+ phosphor-converted white LED based on dual-blue-emitting active layers relative to a single blue-emitting active layer at the same injection current.

Tantalum-doped indium tin oxide ( Ta -doped ITO) transparent conductive films are deposited on glass substrates by electron-beam evaporation. The effects of different Ta concentrations and annealing temperatures on the structural, morphologic, electrical, and optical properties of Ta -doped ITO films are investigated by X-ray diffraction (XRD), atomic force microscope (AFM), Hall measurement, and optical transmission spectroscopy. The obtained films are polycrystalline with a cubic bixbyite structure of indium oxide and preferentially oriented in the (222) crystallographic direction. The minimum resistivity of 1.54×10-4 Ω ·cm is obtained from the ITO film containing 0.2 wt% tantalum annealed at 500°C and the average optical transmittance is over 95% from 425 nm to 460 nm.

The influence of Al pre-deposition on the properties of AlN buffer layer and GaN layer grown on Si (1 1 1) substrate by metalorganic chemical vapor deposition (MOCVD) has been systematically studied. Compared with the sample without Al pre-deposition, optimum Al pre-deposition time could improve the AlN buffer layer crystal quality and reduce the root mean square (RMS) roughness. Whereas, overlong Al-deposition time deteriorated the AlN crystal quality and Al-deposition patterns could be found. Cracks and melt-back etching patterns appeared in the GaN layer grown without Al pre-deposition. With suitable Al-deposition time, crack-free 2.0 μm GaN was obtained and the full-width at half-maximum (FWHM) of (0 0 2) plane measured by double crystal X-ray diffraction (DCXRD) was as low as 482 arcsec. However, overlong Al-deposition time would result in a great deal of cracks, and the crystal quality of GaN layer deteriorated. The surface of GaN layer became rough in the region where the Al-deposition patterns were formed due to overlong Al-deposition time.

The effect of growth rate in the early stage of high temperature (HT) GaN layer growth on the quality of GaN by MOCVD has been investigated. The properties of GaN layers were measured by double crystal X-ray diffraction (DCXRD), Hall method, photoluminescence, and atomic force microscopy, respectively. The results reveal that the quality of GaN layers is influenced by the growth rate of HT GaN growth in the early stage. The properties of GaN layers are obviously improved by decreasing the growth rate in the early stage of HT GaN growth properly. However, when the growth rate decreases to some extent, the quality of GaN layer deteriorates instead. The reasons behind this phenomenon were discussed.

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to enhance COD and nitrogen removal from landfill leachate. To improve denitrification efficiency, the raw leachate with recycled final effluent was pumped into the first-stage UASB (UASB1) to carry out simultaneous denitrification and methanogenesis. The results over 180 d show that the maximum organic removal rate in UASB1 and UASB2 was 12.5 and 8.5 kgCODm(-3)d(-1) in the oxic zone of the A/O reactor, respectively. The COD and biochemical oxygen demand (BOD5) removal efficiency of the system was 80-92% and about 99%, respectively. Without controlling temperature (17-30 degrees C) and dissolved oxygen (0.5-4.0 mgL(-1)), the maximum NH4+-N removal rate was 0.68 kg NH4+-Nm(-3)d(-1), and about 99% of NH4+-N removal was obtained by nearly complete nitritation. The 81-93% total nitrogen removal was obtained by complete denitrification in the UASB1 and in the anoxic zone of the A/O reactor. Fluorescence in situ hybridization (FISH) analysis of the sludge samples from A/O reactor showed that ammonia oxidizing bacteria (AOB) consisted 4% of the eubacterium, while nitrite oxidizing bacteria (NOB) counted less than 0.2% of that. The study shows that the main factors achieving and maintaining nitritation are a proper range of free ammonia concentration obtained by dilution recycled final effluent that inhibits NOB but not AOB; effective control on aeration time by indication of "ammonia valley" on pH profile; and highly efficient denitrification and its reproducing alkalinity to result in pH above 8.5.

The influence of thermal annealing to the characteristics of AlGaInP/GaInP multiple quantum wells (MQWs) light-emitting diode wafers was studied by means of electrochemical capacitance-voltage (ECV) and photoluminescence (PL). Compared with the sample unannealed, the hole carrier concentration of p-GaP layer increased from 5.5x10^1^8 to 6.5x10^1^8cm^-^3, and the hole carrier concentration of p-AlGaInP layer increased from 6.0x10^1^7 to 1.1x10^1^8cm^-^3, after wafer was annealed at 460^oC for 15min in nitrogen. The hole carrier concentrations of p-GaP layers and p-AlGaInP layers did not obviously change when the annealing temperature varied from 460 to 700^oC. However, after the sample was annealed under 780^oC for 15min, the hole carrier concentration of p-GaP layer and p-AlGaInP layer decreased to 8x10^1^7 and 1.7x10^1^7cm^-^3, respectively. At the same time, the diffusion of Mg atoms was observed.

With the methods of compound-melting and high-temperature molding, PC/YAG:Ce fluorescent resin pieces were prepared. The transmittance of the prepared PC/YAG:Ce fluorescent resin in 500~800 nm reaches approximately 65% (0.71 mm thick, double sides polished). The fluorescent resin was characterized by XRD, SEM and PL. The X-ray diffraction (XRD) patterns demonstrated that the fluorescent resin was pure Y3Al5O12 phase. The scanning electron microscopy (SEM) images showed that YAG phosphor was distributed evenly in the fluorescent resin. The excitation spectra had a weak peak at 342 nm and a strong band at 448 nm. The broad emission peaks at about 532 nm can be attributed to 5d--4f transition of Ce3+ ions. Decay curves for the fluorescence of PC/YAG:Ce fluorescent resin show that the lifetime of the fluorescent resin was 61.5 ns. The luminous efficacy of the white LED packaged by the fluorescent resin and blue LED chip was 81.12 lm · W(-1) at 100 mA. All results above of PC/YAG:Ce fluorescent resin indicate a promising fluorescent material for white LEDs.

The blue InGaN light-emitting diodes (LEDs) with specific designs of p-InGaN/GaN superlattice (SL) last quantum barrier are investigated numerically and experimentally. The proposed SL with a graded indium mole fraction from 0% to 5% shows improved efficiency droop and superior optical characteristics in comparison with the conventional LEDs. As indicated by the simulation results, the promotion of hole injection and the reduction of electron leakage play important roles in these improvements. Fabricated LEDs with this specific design exhibit stronger emission intensity, smaller forward voltage, and larger light output power compared to its counterparts.

High-purity ultrafine MgAl2O4 powder was synthesized by metal-alkoxide method and calcining for 2-4 h. And then MgAl2O4/Ce:YAG transparent ceramics were fabricated by hot-pressed sintering and hot isostatic pressed sintering technique with YAG:Ce powder and MgAl2O4 powder. The transparent ceramics were characterized by XRD, SEM, EDS and fluorescence spectrometer, respectively. The results show that the crystal phase of the transparent ceramic was composed of MgAl2O4 and YAG,and the YAG phase dispersed well in the matrix of MgAl2O4. The excitation spectra had a weak band at 345 nm and a strong band at 475 nm. The broad emission peaks at about 533 nm were attributed to 5d--4f transition of Ce3+ ions. Decay curves for the fluorescence of MgAl2O4/Ce:YAG transparent ceramic test show that the lifetime of the Ce:YAG glass ceramic was 59.74 ns. All results show that MgAl2O4/Ce:YAG transparent ceramic may be a promising fluorescent material for white LED applications.