Temporal response of laminated graded-bandgap GaAs-based photocathode with distributed Bragg reflection structure: Model and simulation

To describe the dynamic response characteristics of the laminated graded-bandgap GaAs-based photocathode with distributed Bragg reflection structure, a general theoretical temporal response model is deduced by combining the unsteady continuity equation and numerical calculation method. Through the model, the contribution of the distribution Bragg reflection structure and graded-bandgap emission layer to the temporal response are investigated. Meanwhile, the relationships between the temporal response characteristics of the laminated GaAs-based photocathode and different structural parameters are also analyzed, including average electron decay time, emission layer thickness, and incident light wavelength. It is found that the introduction of distribution Bragg reflection (DBR) layer solves the discrepancy between the absorption capability of the emission layer and the temporal response. Moreover, the distributed Bragg reflection layer can improve the time response by optimizing the initial photoelectron distribution. The improvement effect of the DBR layer on the temporal response is enhanced with the emission layer thickness decreasing or the incident light wavelength increasing. These results explain the effect of the DBR layer of the photocathode on the dynamic characteristics, which can offer a new insight into the dynamic research of GaAs-based photocathode.     

Tapered Bragg reflection waveguide edge emitting lasers with near circular twin-beam emission

An edge emitting laser with two symmetrical near-circular spots located far field （FF） is demonstrated using tapered double-sided Bragg reflection waveguides （BRWs）. The BRWs consist of six pairs of top p-type and bottom n-type A10.Ga0.9 As/A10.3 Ga0.7As Bragg reflectors with a period thickness of 850 nm. The device has a 4° tapered angle configuration and exhibits two stable circular beams with a separation angle of 52°. Typical FF angles of 5.87° and 7.8° in the lateral and vertical directions, respectively, are achieved. The lateral FF angle in the ridged section is independent of the injection current （〉0.8 A） beeause of narrow ridge （-10 μm） confinement. By contrast, the FF angle in the tapered section shows an increase rate of 1.2 1.66°/A. The periodic modulation of the lasing wavelength is observed to be sensitive to self-heating effects.     

RAS在线监测AlGaAs的MOCVD生长

通过瞬态反射各向异性谱和瞬态反射谱在线监测和研究了AlxGa1-xAs的生长过程,利用金属有机化合物汽相淀积技术在GaAs (001)衬底上生长了多层AlxGa1-xAs结构.选择最适合在线监测生长过程的探测光能量,在此探测光能量处所得到的反射各向异性谱和反射谱的信号在生长过程中有很明显的振荡行为产生.研究发现,通过瞬...     

高亮度布拉格反射波导激光器

设计并制备了808 nm波长布拉格反射波导激光器,在垂直方向采用光子带隙效应进行光场限制,实现了超大光模式体积和单横模激射。所制备的10μm条宽、未镀腔面膜的器件在室温、准连续条件下的总输出功率可超过650 mW,最高功率受热扰动限制。激光器垂直方向和水平方向的远场发散角半高全宽分别为8.3°和8.1°,这种近圆形的光束输出可以有效地提高激光器的耦合效率。     

多层AlGaAs的时间分辨归一化反射率及 各向异性反射率谱在线监测及分析

通过光学在线监测技术对多层Al_xGa_1-xAs样品生长过程中的生长速率与表面结构进行了分析。描述了选取合适探测光子能量的方法并在线监测了样品生长过程中表面归一化反射率(Normalized Reflectance, NR)和各向异性反射率(Reflectance Anisotropy,RA)随生长时间的变化,得到了样品的时间分辨NR及RA曲线,利用光学干涉原理解释了NR曲线的振荡衰减特性。不同Al_xGa_1-xAs层NR曲线收敛值随Al组分的单调变化被认为是材料的折射率变化引起的,而RA值随Al组分的增加而增加说明Al原子的并入对表面光学各向异性有影响。通过拟合每一层材料的归一化反射谱振荡曲线得到了各层生长速率,与扫描电镜测试结果差别小于0.02 nm/s。对时间分辨RA曲线分析发现,生长温度对GaAs表面原子结构产生了影响。     

Tapered Bragg reflection waveguide edge emitting lasers with near circular twin-beam emission简

Experiments on developing a frequency-stabilized 555.8-nm laser are presented. The 555.8-nm laser＇ is obtained by frequency doubling of a l lll.6-mn diode laser through single-passing a periodically poled lithium niobate （PPLN） waveguide. Tile 555.8-nm laser is then locked to a stable high-finesse Fabry Perot （FP） cavity by tile Pound Drever--Hall （PDH） technique. Tile finesse of the cavity is measured by tile heterodyne cavity ring-down spectroscopy technique. The linewidth of the 555.8-nm laser is investigated. Alter the laser is locked, the laser line width is reduced to about 3 kHz. This frequency-stabilized 555.8-nm laser is used in experiments on the laser cooling and trapping of ytterbium atoms to develop an ytterbium optical clock.     

1 060 nm高功率垂直腔面发射激光器的有源区设计

对1 060 nm高功率垂直腔面发射激光器的有源区进行了理论计算和设计。对比了GaAsP、GaAs和AlGaAs三种不同材料的垒层所组成的高应变InGaAs量子阱的性能。为了确定有源区阱层和垒层的参数,考虑了自热效应对功率的影响,使得模型更加精确可靠。发现所设计的In_0.28Ga_0.72As量子阱的阱宽和阱数的最佳值分别为9 nm和3个,输出功率可以达到瓦级。另外,对比了三种不同垒层的温度特性,结果显示,使用GaAsP垒层的器件在高温下具有更高的功率和更好的温度稳定性。最后,利用MOCVD生长了InGaAs/GaAsP量子阱并测试了其PL谱,实验数据与理论结果符合得很好。     

布拉格反射波导激光器的光谱特性（英文）

设计并制备了基于双边非1/4波长布拉格反射波导的边发射半导体激光器,中心腔采用低折射率材料,在垂直方向利用布拉格反射进行光限制,实现了超大光斑尺寸且稳定单横模工作。10μm条宽、未镀膜的脊型激光器在准连续和连续工作方式下的总的输出功率分别超过了170 mW和80 mW,且最高功率受热扰动限制。激光器远场图案在垂直方向为双瓣状,单瓣垂直方向和水平方向发散角分别低至7.85°和6.7°。激射谱半高全宽仅为0.052 nm,光谱包络存在周期性调制现象,模式间隔约为3.3 nm。电流增加到300 mA以上时,激光器出现模式跳变。     

新型复合盖层延伸波长InGaAs红外探测器结构优化设计

设计并模拟计算了延伸波长至2.6 μm的复合盖层材料PIN结构In_0.82Ga_0.18As红外探测器,即PNN型盖层、PIN结构的In_0.82Ga_0.18As红外探测器。研究了不同厚度及载流子浓度的PNN盖层对探测器性能的影响。研究结果表明:在In_0.82Al_0.18As厚度为200 nm且载流子浓度为2E18、InAs_0.6P_0.4 厚度为50 nm且载流子浓度为2E17、In_0.82Ga_0.18As厚度为50 nm且载流子浓度为2E16时,探测器表现出最佳的性能。与传统PIN结构探测器相比,其相对光谱响应度仅降低10%,暗电流降低了1个数量级。计算分析了不同工作温度下的暗电流,结果显示:在120~250 K时,暗电流主要为缺陷隧穿电流;在250~300 K时,暗电流主要为带间隧穿电流;当温度大于300 K时,暗电流主要为产生-复合电流和扩散电流。     

高功率垂直外腔面发射半导体激光器增益设计及制备

垂直外腔面发射半导体激光器(vertical external cavity surface emitting laser, VECSEL)兼具高功率与良好的光束质量,是半导体激光器领域的持续研究热点之一.本文开展了光抽运VECSEL最核心的多量子阱增益区设计,对量子阱增益光谱及其峰值增益与载流子浓度及温度等关系进行系统的理论优化,并对5种不同势垒构型的量子阱增益特性进行对比,证实采用双侧GaAsP应变补偿的发光区具有更理想的增益特性.对MOCVD生长的VECSEL进行器件制备,实现了VECSEL在抽运功率为35 W时输出功率达到9.82 W,并且功率曲线仍然没有饱和;通过变化外腔镜的反射率, VECSEL的激光波长随抽运功率的漂移系数由0.216 nm/W降低至0.16 nm/W,证实外腔镜反射率会影响VECSEL增益芯片内部热效应,从而影响VECSEL激光输出功率.所制备VECSEL在两正交方向上的发散角分别为9.2°和9.0°,激光光斑呈现良好的圆形对称性.