A Lateral Regulator Diode with Field Plates for Light-Emitting-Diode Lighting

A lateral current regulator diode （CRD） with field plates is proposed and experimentally demonstrated. The proposed CFtD is based on the junction field-effect transistor （JFET） structure. A cathode field plate is adopted to alleviate the channel-length modulation effect and to improve the saturated I-V characteristics. An anode field plate is induced to achieve a high breakdown voltage VB of the CRD. The influence of the key device parameters on the I-V characteristics of the lateral CRD are discussed. Experimental results show that the proposed CRD presents good I-V characteristics with a high VB about 180 V and a low knee voltage （Vk） below 3 V. Furthermore, the proposed CRD has a negative temperature coefficient. The well characteristic of the proposed CRD makes it a cost-effective solution for light-emitting-diode lighting.

A new dimmer for alternating-current directly driven light-emitting-diode lamp

A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pulse width control (PWM) method. Compared with the conventional phase-controlled dimmer, the proposed PWM dimmer can produce sine wave and did not cause harmonics problem. Furthermore, the proposed control method did not amplify the light flicker due to the independence of input voltage. Therefore, the PWM dimmer can be used as the dimmer of the AC LED lamp instead of the conventional phase-controlled dimmer. The experimental result shows that the proposed PWM dimmer has good performances.

Advances and prospects in nitrides based light-emitting-diodes

Due to their low power consumption,long lifetime and high efficiency,nitrides based white lightemitting-diodes（LEDs） have long been considered to be a promising technology for next generation illumination.In this work,we provide a brief review of the development of GaN based LEDs.Some pioneering and significant experiment results of our group and the overview of the recent progress in this field are presented.We hope it can provide some meaningful information for the development of high efficiency GaN based LEDs and solid-statelighting.

Self-polarized RGB device realized by semipolar micro-LEDs and perovskite-in-polymer films for backlight applications

In backlighting systems for liquid crystal displays,conventional red,green,and blue(RGB)light sources that lack polarization properties can result in a significant optical loss of up to 50%when passing through a polarizer.To address this inefficiency and optimize energy utilization,this study presents a high-performance device designed for RGB polarized emissions.The device employs an array of semipolar blueμLEDs with inherent polarization capabilities,coupled with mechanically stretched films of green-emitting CsPbBr3 nanorods and red-emitting CsPbI3-Cs4PbI6 hybrid nanocrystals.The CsPbBr3 nanorods in the polymer film offer intrinsic polarization emission,while the aligned-wire structures formed by the stable CsPbI3-Cs4PbI6 hybrid nanocrystals contribute to substantial anisotropic emissions,due to their high dielectric constant.The resulting device achieved RGB polarization degrees of 0.26,0.48,and 0.38,respectively,and exhibited a broad color gamut,reaching 137.2%of the NTSC standard and 102.5%of the Rec.2020 standard.When compared to a device utilizing c-plane LEDs for excitation,the current approach increased the intensity of light transmitted through the polarizer by 73.6%.This novel fabrication approach for polarized devices containing RGB components holds considerable promise for advancing next-generation display technologies.

基于TCS3414的石油产品色度测定传感器

针对我国目前石油产品色度目视测定法的不足,设计了一种基于TCS3414数字传感器的透射式色度传感器,改进了石油产品色度测定的关键过程,替代人眼对油品色度进行区分。主要采用CIE-1937色度公式,对测试样品的色度值进行处理;并根据测量要求,采用Light-Emitting-Diode(LED)设计了与之配套的标准光源系统;针对测定要求,编写了相应的测量程序。结果表明,该传感器具有测量速率快、精度高、稳定性好的特点,能够减轻测试人员的劳动强度,同时能够消除观测行为的主观性和不一致性。该种色度传感器具有较大的应用价值。

Interband Optical Transitions due to Donor Bound Excitons in Wurtzite InGaN Strained Coupled Quantum Dots： Strong Built-in Electric Field Effects

Considering the three-dimensional confinement of the electrons and holes and the strong built-in electric field （BEF） in the wurtzite InGaN strained coupled quantum dots （QDs）, the positively charged donor bound exciton states and interband optical transitions are investigated theoretically by means of a variational method. Our calculations indicate that the emission wavelengths sensitively depend on the donor position, the strong BEF, and the structure parameters of the QD system.

Enhanced Green Electrophosphorescence from Oxadiazole-Functionalized Iridium Complex-Doped Devices Using Poly（9,9-Dioctylfluorene） Instead of Poly（N-Vinylcarbazole） as a Host Matrix

Optoelectronic properties of the oxadiazole-functionalized iridium complex-doped polymer light-emitting devices （PLEDs） are demonstrated with two different polymeric host matrices at the dopant concentrations 1-8%. The devices using a blend of poly（9,9-dioctylttuorene）（PFO） and 2-（4-biphenyl）-5-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as a host matrix exhibited a maximum luminance efficiency of 11.3 cd/A at 17. 6 mA/cm^2. In contrast, the devices using a blend of poly（N-vinylcarbazole） （PVK） and PBD as a host matrix reveal only a peak luminance efficiency of 6.Scd/A at 4.1 mA/cm^2. The significantly enhanced electrophosphorescent emissions are observed in the devices with the PFO-PBD blend as a host matrix. This indicates that choice of polymers in the host matrices is crucial to achieve highly efficient phosphorescent dye-doped PLEDs.

Electronic Structures of Wurtzite GaN with Ga and N Vacancies

The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.

Effects of Ag on Electrical Properties of Ag/Ni/p-GaN Ohmic Contact

Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5 × 10^-4 Ωcm^2 is obtained at annealing temperature of 550^o C.

Hole Transport Properties of MEH-PPV at Different Excitation Wavelengths

Using the time-of-flight photocurrent measurements, we investigate the hole transport properties of polymer 2-methoxy, 5-（2＇-ethyl-hexyloxy）-1, 4-phenylene vinylene （MEH-PPV）. The change of hole transport properties from non-dispersive transport to a dispersive type is presented, with the increasing excitation wavelength near the MEH-PPV absorption edge. At room temperature, the effective mobility of MEH-PPV depends on the applied electric field as commonly seen in some organic materials.

Research on Testing System for Three-dimensional Distribution of Luminous Intensity of LED

In terms of asymmetrical three-dimensional distribution(ID) of luminous intensity(LI) of light-emitting-diode(LED),a testing system was conducted in this study. Design and principle of the testing system were introduced. 31 photometers were placed on a concentric circle,and all of them were used to gather LI data of LED at the same time. The data acquisition card(DAC) was used to gather multichannel data and controlled motor. Experimental results indicated that the testing system had achieved the goal of testing three-dimensional distribution of LI. And each parameter could meet the requirements of industrial production and measurement.

A Flip-Chip AlGaInP LED with GaN/Sapphire Transparent Substrate Fabricated by Direct Wafer Bonding

A red-light AIGalnP light emitting diode （LED） is fabricated by using direct wafer bonding technology. Taking N-GaN wafer as the transparent substrate, the red-light LED is flip-chiped onto a structured silicon submount. Electronic luminance （EL） test reveals that the luminance flux is 130% higher than that of the conventional LED made from the same LED wafer. Current-voltage （I- V） measurement indicates that the bonding processes do not impact the electrical property of AIGalnP LED in the small voltage region （V 〈 1.5 V）. In the large voltage region （V 〉 1.5 V）, the I-V characteristic exhibits space-charge-limited currents characteristic due to the p-GaAs/n-GaN bonding interface.

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.

Improved Surface Characteristics and Contact Performance of Epitaxial p-AlGaN by a Chemical Treatment Process

The comparative study of epitaxial 380-run-thick p-Al0.091 Ga0.909 N materials without and with special surface chemical treatment is systematically carried out. After the treatment process, the deep level luminous peak in the 10 K photoluminescence spectrum is eliminated due to the decrease of surface nitrogen vacancy VN related defective sites, while the surface root-mean-square roughness in atomic force microscopy measurement is decreased from 0.395nm to 0.229nm by such a surface preparation method. Furthermore, the performance of surface contact with Ni/Au bilayer metal fihns is obviously improved with the reduction of the Schottky barrier height of 55meV. The x-ray photoelectron spectroscopy （XPS） results show a notable surface element content change after the treatment which is considered to be the cause of the above-mentioned surface characteristics improvement.

Performance Improvement of Bulk Heterojunction Organic Photovoltaic Cell by Addition of a Hole Transport Material

A novel photovoltaic cell with an active layer of poly（phenyleneethynylene） （PPE）/C60/N,N＇-diphenyl-N,N＇-di-（m-tolyl）-p-benzidine （TPD） is designed. In the active layer, PPE is the major component; C60 and TPD are the minor ones. Compared with a control BHJ device based on PPE/C60, the short circuit current density Jsc is increased by 1 order of magnitude, and the whole device performance is increased greatly, however the open circuit voltage Voc is largely decreased. The possible mechanism of the improved performance may be as follows： In the PPE/C60/TPD device, PPE, C60, and TPD serve as the energy harvesting material, the electron transport material, and the hole transport material, respectively. As the TPD and C60 are spatially separated by PPE, the charge recombination is effectively retarded.

Enhanced Spin Injection into ZnO Semiconductor Measured by Magnetoresistance

We prepare 2× （NiFe/CoZnO）/ZnO/（CoZnO/Co）×2 spin valve structures used for spin injection by sputtering and photolithography. In the junctions, the free magnetic layer 2× （NiFe/CoZnO） and the fixed magnetic layer （CoZnO/Co） × 2 are used to realize the spin valve functions in the external switch magnetic field. Since the wide gap semiconductor ZnO layer is located between the two magnetic semiconductor layers CoZnO, the electrical ,spin injection from the magnetic semiconductor CoZnO into the non-magnetic semiconductor ZnO is realized. Based on the measured magnetoresistance and the Schmidt model, the spin polarization ratio in the ZnO semiconductor is deduced to be 11.7% at 90K and 7.0% at room temperature, respectively.

MOCVD Growth and Characterization of Epitaxial AlxGa1-xN Films

We study the growth of AlxGa1-x N epilayers on （0001） sapphire by low-pressure MOCVD, using a lowtemperature AIN buffer. By varying the input flow rates of trimethylgallium （TMGa）, we obtain crack-free AlGaN films in the whole range of composition. A linear relationship between gas and solid Al content is observed. The structural properties of the layers （x =0- 1） are investigated by x-ray diffraction, atomic force microscopy （AFM） and scanning electron microscopy （SEM）. It is found that a two-direction growth appears along the c-axis and the （1011） directions for x ≥ 0.45. From the results of Raman spectroscopy, we suggest that the compressive stain and the lack of mobility orAl adatoms can induce the formation of （1011） grains.

Electroluminescence of an n-ZnO/p-GaN Heterojunction under Forward and Reverse Biases

Electroluminescent characteristics of n-ZnO/p-GaN heterojunctions under forward and reverse biases are studied. Emissions at 389nm and 57Ohm are observed under forward bias. An unusual emission at 390ram appears under reverse bias, and is attributed to the recombination in the p-GaN side of the heterojunction. The yellow emission peaked at 57Ohm is suppressed under reverse bias. The light intensity exponentially depends on the reverse current. The emission under reverse bias is correlated to tunnelling carrier transport in the heterostructure. Our results also support that the well-known yellow band of GaN comes from the transitions between some near-conduction-band-edge states and deep localized acceptor states.

Columnar Structures and Stress Relaxation in Thick GaN Films Grown on Sapphire by HVPE

Thick GaN films with high quality are directly grown on sapphire in a home-built vertical hydride vapour phase epitaxy （HVPE） reactor. The optical and structural properties of large scale columnar domains near the interface are studied using cathodoluminescence and micro-Raman scattering. These columnar domains show a strong emission intensity due to extremely high free carrier concentration up to 2 × 10^19 cm^-3, which are related with impurities trapped in structural defects. The compressive stress in GaN film clearly decreases with increasing distance from interface. The quasi-continuous columnar domains play an important role in the stress relaxation for the upper high quality layer.

Three-Step Growth Optimization of AlN Epilayers by MOCVD

A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low temperature （LT） A1N nucleation layer （NL）, and two high temperature （HT） A1N layers with different V/Ⅲ ratios. Our results reveal that the optimal NL temperature is 840-880℃, and there exists a proper growth switching from low to high V/Ⅲ ratio for further reducing threading dislocations （TDs）. The screw-type TD density of the optimized AIN film is just 7.86×10^6 cm^-2, about three orders lower than its edge-type one of 2×10^9 cm^-2 estimated by high-resolution x-ray diffraction （HRXRD） and cross-sectional transmission electron microscopy （TEM）.