The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

The scalability of the tunnel-regenerated multi-active-region （TRMAR） structure has been investigated for the application in light-emitting diodes （LEDs）. The use of the TRMAR structure was proved theoretically to have unique advantages over conventional slngle-active-layer structures in virtually every aspect, such as high quantum efficiency, high power and low leakage. Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.     

High power AlGaInP laser diodes with zinc-diffused window mirror structure

The technology of zinc-diffusion to improve catastrophic optical damage (COD) threshold of compressively strained GaInP/AlGaInP quantum well laser diodes has been introduced. After zinc-diffusion, about 20 μm-long region at each facet of laser diode has been formed to serve as the window of the lasing light. As a result, the COD threshold has been significantly improved due to the enlargement of bandgap by the zinc-diffusion induced quantum well intermixing, compared with that of the conventional non-window structure. 40-mW continuous wave output power with the fundamental transverse mode has been realized under room temperature for the 3.5μm-wide ridge waveguide diode. The operation current is 84 mA and the slope efficiency is 0.74 W/A at 40 mW. The lasing wavelength is 656 nm.     

Performance improvement of InGaN blue light-emitting diodes with several kinds of electron-blocking layers

The performance of InGaN blue light-emitting diodes(LEDs) with different kinds of electron-blocking layers is investigated numerically.We compare the simulated emission spectra,electron and hole concentrations,energy band diagrams,electrostatic fields,and internal quantum efficiencies of the LEDs.The LED using AlGaN with gradually increasing Al content from 0% to 20% as the electron-blocking layer(EBL) has a strong spectrum intensity,mitigates efficiency droop,and possesses higher output power compared with the LEDs with the other three types of EBLs.These advantages could be because of the lower electron leakage current and more effective hole injection.The optical performance of the specifically designed LED is also improved in the case of large injection current.     

High power 2-μm room-temperature continuous-wave operation of GaSb-based strained quantum-well lasers

A high power GaSb-based laser diode with lasing wavelength at 2 μm was fabricated and optimized. With the optimized epitaxial laser structure, the internal loss and the threshold current density decreased and the internal quantum efficiency increased. For uncoated broad-area lasers, the threshold current density was as low as 144 A/cm2 (72 A/cm2 per quantum well), and the slope efficiency was 0.2 W/A. The internal loss was 11 cm-1 and the internal quantum efficiency was 27.1%. The maximum output power of 357 mW under continuous-wave operation at room temperature was achieved. The electrical and optical properties of the laser diode were improved.     

Improving InGaN-LED performance by optimizing the patterned sapphire substrate shape

The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates (PSSes) with different values of fill factor (f) and slanted angle (θ) are investigated in detail. The threading dislocation (TD) density is lower in the film grown on the PSS with a smaller fill factor, resulting in a higher internal quantum efficiency (IQE). Also the ability of the LED to withstand the electrostatic discharge (ESD) increases as the fill factor decreases. The illumination output power of the LED is affected by both θ and f. It is found that the illumination output power of the LED grown on the PSS with a lower production of tanθ and f is higher than that with a higher production of tanθ and f.     

InGaN/GaN laser diode characterization and quantum well number effect

The effect of quantum well number on the quantum efficiency and temperature characteristics of In- GaN/GaN laser diodes （LDs） is determined and investigated. The 3-nm-thick In0.13Ca0.87N wells and two 6-am-thick GaN barriers are selected as an active region for Fabry-Perot （FP） cavity waveguide edge emitting LD. The internal quantum efficiency and internal optical loss coefficient are extracted through the simulation software for single, double, and triple InGaN/GaN quantum wells. The effects of device temperature on the laser threshold current, external differential quantum efficiency （DQE）, and output wavelength are also investigated. The external quantum efficiency and characteristic temperature are improved significantly when the quantum well number is two. It is indicated that the laser structures with many quantum wells will suffer from the inhomogeneity of the carrier density within the quantum well itself which affects the LD performance.     

Efficiency and droop improvement in a blue InGaN-based light emitting diode with a p-InGaN layer inserted in the GaN barriers

The advantages of a blue InGaN-based light-emitting diode with a p-InGaN layer inserted in the GaN barriers is studied. The carrier concentration in the quantum well, radiative recombination rate in the active region, output power, and internal quantum efficiency are investigated. The simulation results show that the InGaN-based light-emitting diode with a p-InGaN layer inserted in the barriers has better performance over its conventional counterpart and the light emitting diode with p-GaN inserted in the barriers. The improvement is due to enhanced Mg acceptor activation and enhanced hole injection into the quantum wells.     

810-nm InGaAlAs/AlGaAs double quantum well semiconductor lasers with asymmetric waveguide structures

The 810-nm InGaAlAs/AlGaAs double quantum well （QW） semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conver- sion efficiency at continuous-wave （CW） power output. The threshold current density and slope efficiency of the device are 180 A/cm^2 and 1.3 W/A, respectively. The internal loss and the internal quantum efficiency are 1.7 cm^-1 and 93%, respectively. The 70% maximum power conversion efficiency is achieved with narrow far-field patterns.     

Improved performance of InGaN light-emitting diodes with a novel sawtooth-shaped electron blocking layer

A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes （LEDs）. The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the electron leakage, and the internal quantum efficiency are systematically studied. The simulation results show that the LED with a sawtooth-shaped electron blocking layer possesses higher output power and a smaller efficiency droop than the LED with a conventional A1GaN electron blocking layer, which is because the electron confinement is enhanced and the hole injection efficiency is improved by the appropriately modified electron blocking layer energy band.     

Influence of the KTP crystal boundary temperature on conversion efficiency in high power green laser

The influence of the KTiOPO4 (KTP) crystal boundary temperature on conversion efficiency in high power green laser has been studied theoretically and experimentally. Temperature distribution inside the KTP crystal has been analyzed by solving the thermal conductivity equation. From the temperature distribution inside the KTP crystal, we have calculated the optimal phase-matching angles of the type-Ⅱ KTP crystal as a function of temperature. The second-harmonic conversion efficiency as a function of temperature has also been calculated. In the experiment, two KTP crystals with different phase-matching angles were used in the intrcavity-frequency-doubled resonator. When the boundary temperature of KTP-A (φ = 23.6°,θ = 90° under the condition of 27 ℃ temperature) was setting at 4 ℃, a maximum green light power of 104 W was generated at repetition rate of 20.7 kHz and pulse width of 132 nm with pumping current of laser diode of 18.3 A, leading to 10.2% optical-to-optical conversion efficiency. When KTP-B crystal (φ = 24.68°, θ = 90° under the condition of 80 ℃ temperature) was employed, an average output power of 110 W at 532 nm has been achieved with values of 11.5% and 2% for the optical-to-optical efficiency and the instability, respectively. The optimal boundary temperature of this KTP crystal has been found to be 48.8 ℃.     

AlGaInP大功率发光二极管发光效率与结温的关系

目前,AlGaInP大功率发光二极管(LED)存在的主要问题是大电流工作时发热严重,主要是由于电流扩展不均匀、出光面电极对光子的阻挡和吸收以及器件材料与空气折射率之间的差距引起的全反射现象,这些因素造成大功率LED出光受到限制、发光效率低、亮度不高.提出了一种复合电流扩展层和复合分布式布拉格反射层(DBR)的新型结构LED,使得注入电流在有源区充分地扩散,同时提高了常规单DBR对光子的反射率.结果显示,这种新型结构LED比常规结构LED的性能得到了很大的提升,350 mA注入电流下两者的输出光功率分别为4 关键词： 复合电流扩展层 复合分布式布拉格反射层 出光效率 结温     

全息技术制作二维光子晶体蓝宝石衬底提高发光二极管外量子效率

为了提高GaN基发光二极管(LED)的外量子效率,在蓝宝石衬底制作了二维光子晶体.衬底上的二维光子晶体结构采用激光全息技术和感应耦合等离子体(ICP)干法刻蚀技术制作,然后采用金属氧化物化学气相沉积(MOCVD)技术在图形蓝宝石衬底(PSS)上生长2μm厚的n型GaN层,4层量子阱和200nm厚的p型GaN层,形成LED结构.衬底上制作的二维光子晶体为六角晶格结构,晶格常数为3.8μm,刻蚀深度为800nm.LED器件光强输出测试结果显示,在PSS上制作的LED(PSS-LED)的发光强度普遍高于蓝宝石平 关键词： 全息 发光二极管 图形蓝宝石衬底 外量子效率     

结温与热阻制约大功率LED发展

LED结温高低直接影响到LED出光效率、器件寿命、可靠性、发射波长等。保持LED结温往允许的范围内,是大功率LED芯片制备、器件封装和器件应用等每个环节都必须重点研究的关键因素,尤其是LED器件封装和器件应用设计必须着重解决的核心问题。首先介绍pn结结温对LED器什性能的影响,接着分析大功率LED结温与器件热阻的关系．基于对器件热阻的分析,得出了结温与热阻已经制约大功率LED进一步向更大功率发展的结论,并提出了如下两个观点：1．要在保持低成本和自然散热方式下提高LED器件的功率,根本的出路是提高光转换效率;2．在日前没有提高光转换效率的情况下,发展超过5W的大功率器件对工程应肘没有实质意义。     

Status of GaN-based green light-emitting diodes

GaN-based blue light emitting diodes(LEDs) have undergone great development in recent years,but the improvement of green LEDs is still in progress.Currently,the external quantum efficiency(EQE) of GaN-based green LEDs is typically30%,which is much lower than that of top-level blue LEDs.The current challenge with regard to GaN-based green LEDs is to grow a high quality In GaN quantum well(QW) with low strain.Many techniques of improving efficiency are discussed,such as inserting Al GaN between the QW and the barrier,employing prestrained layers beneath the QW and growing semipolar QW.The recent progress of GaN-based green LEDs on Si substrate is also reported:high efficiency,high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2,and the relevant techniques are detailed.     

Spectral dependence of light extraction efficiency of high‐power III‐nitride light‐emitting diodes

Using the recently suggested method of processing the data on external quantum efficiency as a function of output optical power, we have estimated the dependence of light extraction efficiency of high‐power light‐emitting diodes (LEDs) on their emission wavelength varied between 425 nm and 540 nm. The extraction efficiency is found to increase with the wavelength from ～80% to ～85% in this spectral range and to correlate with the wavelength dependence of reflectivity of the large‐area p‐electrode being the essential unit of the LED chip design. The correlation found identifies the incomplete reflection of emitted light from the electrode as the major mechanism eventually controlling the spectral dependence of the efficiency of light extraction from the LEDs.

     

Performance enhancement of blue light-emitting diodes by adjusting the p-type doped last barrier

Blue light-emitting diodes (LEDs) with different p-doping concentrations in the last barrier have been studied numerically. The energy band diagrams, carrier concentrations, internal quantum efficiency and light output power are investigated using APSYS software. The simulation results show that the LED structure with p-doping in the last barrier has a better hole-injection efficiency and confinement of electron leakage over the structure with the last undoped GaN barrier due to enhancement of the holes’ injection and the electrons’ confinement. As a result, the efficiency droop is markedly improved, and the light output power is greatly enhanced when a larger p-doping amount is centralised in the last barrier.     

The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

The scalability of the tunnel-regenerated multi-active-region (TRMAR) structure has been investigated for the application in light-emitting diodes (LEDs). The use of the TRMAR structure was proved theoretically to have unique advantages over conventional single-active-layer structures in virtually every aspect, such as high quantum efficiency, high power and low leakage. Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.     

Reduction of surface defects on the GaP window layer of 630 nm AlGaInP LED using post-Zn diffusion process

We have investigated the characteristics of the surface of the GaP window layer of 630 nm AlGaInP LED, which was improved by post-Zn diffusion process. The measured resistance and the amount of hole concentration of the post-Zn-diffused GaP window layer have remarkably decreased and increased, respectively. Moreover, the ECV system showed that the amount of doping concentrations on the surface of the GaP window layer was significantly increased because of the diffusion of Zn atoms. The amount of surface defects observed on the post-Zn-diffused GaP window layer was also reduced. Furthermore, it was found out that the efficiency of 630 nm AlGaInP LED chip was increased due to the surface improvement of the GaP window layer. At an injection current of 40 mA, the LED chip with a Zn diffusion layer obtained a higher output power of 11 mW compared to the 7.5 mW output of the conventional LED chip.