新型垂直腔面发射激光器的最优化设计模式

本文通过提出具有优点为微分量子效率可以大于l的一种新型多有源区隧道再生应变量子阱垂直腔面发射半导体激光器(VCSELs)结构，可得到阈值电流更小、输出功率更大的器件。同时，通过对这种器件功率效率的分析，总结出针对这种新型结构的以固定工作电流及串联电阻为参数的最优化DBR反射率公式，并且就功率效率与工作电流、串联电阻及反射率的关系进行了讨论，这将对器件的合理设计以及器件制备具有实质性的指导作用。     

Improvement of InGaN-GaN light-emitting diode performance with a nano-roughened p-GaN surface

This investigation describes the development of InGaN-GaN light-emitting diode (LED) with a nano-roughened top p-GaN surface which uses Ni nano-mask and wet etching. The light output of the InGaN-GaN LED with a nano-roughened top p-GaN surface is 1.4 times that of a conventional LED, and wall-plug efficiency is 45% higher. The operating voltage of InGaN-GaN LED was reduced from 3.65 to 3.5 V at 20 mA and the series resistance was reduced by 20%. The light output is increased by the nano-roughening of the top p-GaN surface. The reduction in the series resistance can be attributed to the increase in the contact area of nano-roughened surface.     

The dependence of the photocurrent of MIS solar cells on thickness of Schottky barrier metals

The thickness of the barrier metals on the Schottky solar cells is very critical to the conversion efficiency. A theoretical calculation of the short circuit current of the Schottky barrier solar cells on applying Fuchs-Sondheimer's theory to calculate the electrical resistivity in thin metal films, and Handy's approach to calculate the series resistance on a given configuration of the contact grids shows that the optimum thickness which gives maximum short circuit current closely depends onthe intensity of the illuminating light and on the series resistance of the device. The optimum thickness shifts toward thicker film as the illuminating light or the series resistance increases. Fabrication of these devices on MIS solar cells indicates that the monitored optimum thickness satisfactorily agrees with the theoretical values.     

980 nm大功率半导体激光器增透膜的优化设计与制备

对于大功率半导体激光器,根据其最佳工作点随着和端面反射率相关的阈值电流等参数的变化规律,选择适合的腔面膜反射率系数进行设计。设计并制备三种腔面膜膜系,它们的增透膜在980 nm处反射率系数分别为8%、5%与2%,高反膜反射率系数均为90%。器件封装后分别测试其发光性能,数据显示与未镀膜的激光器相比,镀膜后的激光器在输入15 A电流时,它们的输出功率提高了35.18%~37.35%;它们在其最佳工作点处转换效率提高了25.33%~27.44%;此外高反膜反射率一定时,它们达到最佳工作点所需的电流值随其增透膜反射率系数减小而增大,结果表明优化选取合适的半导体激光器腔面膜膜系进行镀制,可以使半导体激光器在最佳工作点具有更大的输入电流,从而更适合在大功率工作。     

不同反射率双面太阳电池背面综合转换效率差异性研究

双面太阳电池是指硅片的正面和反面都可以接受光照并产生光生电压和电流的太阳电池,由于受到结构等各种因素的影响,目前还没有完善的测试方案用于双面太阳电池的完整测试。基于太阳能仿真环境PC1D,采用控制变量的方法来测定电池背面反射率对双面太阳电池综合转换效能的影响,研究了双面电池在不同背面受光条件下的测试结果,得出电池背面背景反射率增大时,双面太阳电池的综合转换效能的变化规律;确定了双面电池合理的测试条件,给出了双面电池科学的测试方案。结论对双面太阳电池的测试和应用具有重要意义。     

On Load Adaptive Control of Voltage Regulators for Power Managed Loads: Control Schemes to Improve Converter Efficiency and Performance

Voltage regulator (VR) efficiency improvement especially at light load currents is important in many applications including those that are battery powered and have energy consumption constraints. However, controlled steady-state and dynamic performance should be maintained while improving efficiency. In this paper, an analytical study of VR losses and voltage ripple deviation is presented and discussed, yielding to proposed control technique, namely "pulse sliding" (PSL) control technique, which results in improved VR conversion efficiency with low and controlled voltage ripple and improved dynamic response. The proposed method and controller achieves the advantages of both variable frequency and fixed frequency controls and eliminates their disadvantages by utilizing information obtained from the inductor peak current, compensation error signal and capacitor current, resulting in an optimum nonlinear switching frequency modulation. PSL is compared to other control methods by both analysis and experiments. Experimental results highly agree with theoretical analysis.     

Optimization of planar Be-doped InGaAs VCSEL's with two-sidedoutput

Threshold current, output power, wall-plug efficiency and operating voltage of epitaxially grown InGaAs-AlGaAs planar vertical-cavity surface-emitting lasers (VCSEL's) are strongly influenced by the electrical and optical properties of the p-doped Bragg reflector. Here we study in some detail the dependence of output behavior on the composition, interface grading, and modulation doping of the Be-doped AlGaAs-GaAs Bragg reflector. Using optimized p-doped mirrors VCSEL's with low threshold current densities of 300 A/cm² , low driving voltages of 1.6 V and high wall-plug efficiencies of 17.6% are obtained. Transverse single-mode emitting devices show a record low emission linewidth of 30 MHz and a linewidth-power product of 2.2 mW·MHz     

高功率窄脉冲垂直腔面发射激光器n-DBR反射率的优化

从理论上研究了n型分布布拉格反射镜(n-DBR)的反射率对器件阈值电流、输出功率以及转换效率的影响,得出了最佳反射率。在此基础上研制了垂直腔面反射激光器(VCSEL)单管和阵列器件,采用波形分析法对VCSEL器件的功率进行了测试。在脉冲宽度60ns,重复频率100Hz条件下,500μm口径单管器件在注入电流为110A时,峰值输出功率达102W,功率密度为52kW/cm2,4×4、5×5阵列器件在100A时,功率分别达到98W和103W。对比了单管器件在连续、准连续和脉冲工作条件下的输出特性和光谱特性,连续和准连续条件下激射波长的红移速率分别为0.92nm/A和0.3nm/A,6A时的内部温升分别为85℃和18℃,而脉冲条件下激射波长的红移速率仅为0.0167nm/A,6A时的温升为1.5℃,远小于连续和准连续的情况,这也是器件在脉冲条件下能得到很高输出功率的主要原因。     

交流LED与高压LED的特性实验研究

高压LED和交流LED都是通过串联数十颗LED来增大整体导通电压,结构上高压LED是交流LED的一种特殊形式。介绍了高压LED和交流LED的驱动电路模型,其共同点是皆有一个限流电阻与光源串联。通过调整限流电阻的阻值和改变光源所含LED个数与连接形式,分别对高压LED和交流LED的输出特性进行了测量。在两种光源所含LED数量和工作电流均相同的情况下,高压LED的发光效率和光通量要高于交流LED;并联式高压LED的发光效率低于串联式高压LED的发光效率,光通量则相反;验证了交流LED的发光效率与限流电阻无关。     

Configurable three-wavelength Raman fiber laser for Ramanamplification and dynamic gain flattening

A three-wavelength Raman fiber laser is presented that is suitable for the generation of a flattened Raman gain curve over a broad range of extended telecommunications bandwidths. This laser utilizes an 1100-nm Yb-doped cladding pumped fiber laser and a cascaded Raman resonator to generate output radiation at 1427, 1454, and 1480 nm. The slope efficiency for conversion from the 1100- to 14xx-nm radiation is 0.38, the total output power is 1.1 W, and the fiber laser "wall-plug" efficiency is 0.10. The output power at 1454 and 1480 nm is adjusted by varying the reflectivity of the fiber grating output couplers and the suppression of lower order spectral components is between 15 and 20 dB. Low frequency relative intensity noise (RIN) measurements indicate RIN values less than -90 dB/Hz below 100 kHz     

准连续半导体激光器的传导冷却封装优化

为了提高准连续输出功率为×102W量级的半导体激光器的输出功率和可靠性,采用双面散热方式提高传导冷却封装的散热能力。结果表明,采用改进的封装方式后,激光器的最高输出功率由91.6 W提高到98.4W,阈值电流由15.6 A减小到15.1 A,斜率效率由1.09 W/A提高到1.16 W/A,插头效率略有增加。激光器在100 A工作电流时,有源区的温度和激光器的热阻都有所减小,说明改进的封装方式具有更好的散热性能。     

环形谐振腔中结构特征参数的优化设计

利用光纤环形腔半导体激光器(FRSLs)模型,同时考虑到增益介质端面剩余反射率、系统光路的耦合效率和耦合分光比的影响,对FRSLs速率方程进行理论计算,提出优化结构特征参数,调控环形腔损耗、阈值、外量子效率和输出功率的方案。给出了剩余反射率对最大腔增益和增益稳定度的制约关系。此外,从实验上证实阈值电流与分光比倒数的对数满足线性关系。理论分析结果较好地预测了器件的性能。     

Optimization of silicon solar cell design for use under concentrated sunlight

For efficient operation under concentrated sunlight, solar cells must be optimized in terms of the collection efficiency and series resistance. At low concentrations, collection efficiency is more important, however, series resistance becomes increasingly important at high intensities ultimately limiting the device output. At a given intensity a tradeoff between these properties results in optimum performance. The computations includes losses from recombination, series resistance, contact coverage, and reflection. There are nine design parameters that were optimized; junction depth, thickness of anti-reflecting coating, width of grid strips, width of contact strips, separation of grid strips, length of grid strips, wafer thickness, and doping concentration of both sides of the junction. An optimization computer program was used to find the optimum design by employing a sequential search technique. An example is given for the optimum design of a silicon solar cell operating under an incident intensity of 9 W/cm²with active and total area efficiencies of 12.8 and 11.6 percent. Active area efficiencies as high as 17.8 percent are possible but with lower total area efficiencies. The effect of each of the nine parameters on device performance is presented. The theory was confirmed by fabricating and testing experimental devices. When corrected for temperature, the theory accurately predicts device performance to intensities of 50 suns (5.2 W/cm²).     

Enhanced Light Extraction in Wafer-Bonded AlGaInP-Based Light-Emitting Diodes via Micro- and Nanoscale Surface Textured

AlGaInP-based metal-bonding light-emitting diodes (LEDs) with micro- and nanoscale textured surface were investigated. The device surface with microbowls and nanorods were formed by a chemical wet-etching and dry-etching technique for enhancing light-extraction purpose. The luminous intensity could be enhanced 65.8% under 20-mA current injection as compared with the plane surface LEDs. The maximum wall-plug efficiency was achieved 14.1% at 7.5-mA operation.     

Optimum Design of Dye‐Sensitized Solar Module for Building‐Integrated Photovoltaic Systems

This paper presents a method for determining the optimum active‐area width (OAW) of solar cells in a module architecture. The current density–voltage curve of a reference cell with a narrow active‐area width is used to reproduce the current density profile in the test cell whose active area width is to be optimized. We obtained self‐consistent current density and electric potential profiles from iterative calculations of both properties, considering the distributed resistance of the contact layers. Further, we determined the OAW that yields the maximum efficiency by calculating efficiency as a function of the active‐area width. The proposed method can be applied to the design of the active area of a dye‐sensitized solar cell in Z‐type series connection modules for indoor and building‐integrated photovoltaic systems. Our calculations predicted that OAW increases as the sheet resistances of the contact layers and the intensity of light decrease.     

Enhanced efficiency of UV second harmonic and sum frequencygeneration from copper vapor lasers

The authors have generated over 460-mW output power at 255.1 and 271.2 nm with a wall-plug efficiency of 0.016% and 300 mW at 289.1 nm with a wall-plug efficiency of 0.0008%. Using an off-axis unstable resonator matched to the plasma-tube geometry and gain characteristics along with focusing lenses with reduced achromatic and spherical aberration has allowed the highest efficiencies for nonlinear UV generation from a CVL (copper vapor laser) reported to date. Current UV output powers are limited by crystal damage which may be reduced by modifying the delivery optics     

1D VRM非轴对称虚共焦腔(Nd，Ce)：YAG板条激光器的实验研究

对(Nd,Ce):YAG板条固体激光器提出了一维变反射率镜(1D VRM)非轴对称虚共焦腔,并与平行平面腔和旋转对称变反射率镜(2D VRM)虚共焦腔等腔型作了实验比较研究。结果表明,1D VRM虚共焦腔适音板条固体激光器, 兼顾输出激光效率和光束质量。     

Uniform wafer-bonded oxide-confined bottom-emitting 850-nm VCSELarrays on sapphire substrates

Uniform bottom-emitting 850-nm vertical-cavity surface-emitting laser (VCSEL) arrays on sapphire substrates have been demonstrated using wafer bonding technology to transfer the epitaxially-grown VCSEL structures from GaAs substrates onto sapphire substrates. The uniformity of the VCSEL arrays were improved by placing thin oxide aperture at the standing wave node to reduce scattering loss for small aperture devices. The averaged threshold current of a 5×5 VCSEL array is as low as 346 μA, while the averaged external quantum efficiency approaches 57%. The maximum wall-plug efficiency is 25% and the single-mode output power is more than 2 mW under continuous-wave current excitation at room temperature. We have also demonstrated a large (10×20) VCSEL array with variations of threshold current and external quantum efficiency less than 4% and 2%, respectively     

Comparison of potential solar electricity output from fixed‐inclined and two‐axis tracking photovoltaic modules in Europe

We present an approach to determine the potential energy gains of flat plate non‐concentrating photovoltaic systems for the case of two‐axis tracking and two inclination angles with fixed orientation (assuming biannual adjustment) compared to the configuration of single fixed optimum angle. The calculation is based on the Photovoltaic Geographic Information System (PVGIS), which integrates modelling tools with the pan‐European solar radiation database. The results indicate that in the case of a PV system with two seasonal inclination angles, the maximum yearly gains, compared to the single fixed optimum angle, do not exceed 60–70 kWh per kW_p in the Mediterranean region, while in the Baltic and North Sea regions this configuration gives less than 20 kWh extra. For the case of two‐axis tracking, the relative energy gain compared to single fixed optimum angle is highest in the Northern latitudes but the absolute gain is much higher in the South. Typical yearly gains in Portugal and the Mediterranean region are in the range of 400–600 kWh per kW_p. The smallest absolute increase is found in the Northwest and Central Europe including the British Isles, where it is lower than 250 kWh per kW_p. For crystalline silicon we also investigate the effects of temperature and shallow‐angle reflectivity on the comparison between fixed and tracking systems. While both effects reduce the overall energy output, the temperature degradation is stronger for tracking systems while the reflectivity reduces output more for fixed systems. The combined effect is almost equal for fixed and two‐axis tracking systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Nonlinear analysis of the avalanche transit-time oscillator

The nonlinear operating characteristics of the avalanche transit-time oscillator are studied by means of Fourier-series representation. For optimum operation, the oscillator must be designed such that start-oscillation conditions are satisfied simultaneously at the first and the second harmonic of the desired oscillation frequency. Under those conditions the oscillation frequency does not depend on the dc bias current; the signal level increases smoothly with bias current. For large signals, the diode exhibits negative resistance for frequencies substantially below the avalanche frequency; the oscillation frequency therefore may be below the avalanche frequency corresponding to the dc bias current required for large-signal operation. A condition for attaining large-signal operation is that the product of drift-zone capacitance and total load resistance must be small compared to the oscillation period; this condition also yields small starting currents. The output power at the oscillation frequency is obtained explicitly in terms of diode and external circuit parameters. The maximum attainable output power is limited by parasitic series resistance and by permissible RF voltage swing as compared to dc bias voltage. The best power-impedance product is obtained by choosing the transit angle equal to 0.74 π. In practice, it may be advantageous to choose a smaller value for the transit angle, in order that the tuning condition for the second harmonic may be more easily satisfied. The dc-to-RF conversion efficiency in principle is linearly proportional to the dc current density; the maximum efficiency again is limited by parasitic series resistance and by permissible RF voltage swing.