垂直腔面发射激光器DBR的生长优化

基于能带理论和分布布拉格反射镜(DBR)的工作原理,分析了垂直腔面发射激光器(VCSEL)中DBR串联电阻较大的原因。采用组分渐变降低DBR结构中异质结界面处势垒,优化DBR的各层掺杂浓度,通过调控费米能级进一步降低DBR中的异质结势垒,从而有效降低DBR串联电阻。实验采用Al_(0.22)Ga_(0.78)As/Al_(0.9)Ga_(0.1)As作为生长DBR的两种材料,设计了DBR各层厚度,研究了AlGaAs材料的最佳生长温度,利用MOCVD外延技术完成了795nm VCSEL突变DBR与渐变DBR的生长。经过工艺制备,测得突变DBR和渐变DBR的电阻分别为6.6和5.3Ω,优化生长后的DBR电阻得到有效降低。     

垂直腔面发射激光器DBR的优化设计

模拟分析了垂直腔面发射激光器分布布拉格反射镜铝组分不同分布对价带的影响,并对两种不同结构的器件进行了测试,测试结果表明抛物线渐变结构可以有效降低价带的势垒,进而可以改善垂直腔面发射激光器的电流热效应,为实现室温连续工作打下基础。     

940 nm VCSEL中DBR的反射特性分析

应用传输矩阵法计算并分析了分布式布拉格反射镜(DBR)的堆叠方式对反射谱的影响，当入射介质为GaAs材料、出射介质为空气时，DBR以低折射率层/高折射率层(LH)的方式排列具有更高的反射率。研究了入射角度对DBR反射率的影响，利用角度相关的传输矩阵模型对DBR反射谱进行计算，结果表明，DBR反射谱随着入射角度的增加而蓝移，最大反射率随着入射角度的增加而增大。建立了940 nm波长下Al_xGaAs的材料折射率与铝的原子数分数x之间的线性拟合模型，并通过多层剖分等效法，计算分析了渐变层对DBR反射谱特性的影响。相比于突变型DBR结构，渐变型DBR结构在维持最高反射率基本不变的情况下，反射带宽有所减小。     

组份渐变电子阻挡层对InGaN/GaN LED光电特性的影响

利用数值模拟方法,研究组份渐变电子阻挡层(EBL)对InGaN/GaN发光二极管电学和光学特性的影响。结果表明,三角形组份渐变EBL结构能有效减小器件的开启电压,提高光输出功率,改善高注入电流水平下发光效率的下降情况。能带模拟结果进一步表明,三角形组份渐变EBL结构显著提高了导带底的电子势垒,可有效限制电子向P型GaN层的泄露,同时减小了价带顶的空穴势垒,可增强P型GaN层的空穴向有源区的注入效率,改善其在量子阱内的浓度分布。     

数值分析渐变DBR对垂直腔面发射激光器谐振腔模的影响

通过数值分析研究了含线性渐变层的Al0.9Ga0.1As/AlyGa1-yAs/GaAs/AlxGa1-xAS DBR的光学特性及其对VCSEL谐振腔光学特性的影响,建立了渐变型DBR渐变层厚度与折射率的关系,通过特征矩阵法计算了突变GaAs/Al0.9Ga0.1AS DBR和渐变型DBR的反射谱和反射相移,分析了渐变层对DBR反射率和反射相移的影响.对渐变型DBR,要使VCSEL谐振腔满足中心波长相位匹配条件,还需要在DBR靠近谐振腔一侧的最前面增加一定厚度的渐变层,称为相位匹配层.通过计算,我们得到了使VCSEL谐振腔满足相位匹配条件时均匀层和相位匹配层的厚度.     

数值分析渐变DBR对垂直腔面发射激光器谐振腔模的影响

通过数值分析研究了含线性渐变层的Al0.9Ga0.1As/AlyGa1-yAs/GaAs/AlxGa1-xAS DBR的光学特性及其对VCSEL谐振腔光学特性的影响,建立了渐变型DBR渐变层厚度与折射率的关系,通过特征矩阵法计算了突变GaAs/Al0.9Ga0.1AS DBR和渐变型DBR的反射谱和反射相移,分析了渐变层对DBR反射率和反射相移的影响.对渐变型DBR,要使VCSEL谐振腔满足中心波长相位匹配条件,还需要在DBR靠近谐振腔一侧的最前面增加一定厚度的渐变层,称为相位匹配层.通过计算,我们得到了使VCSEL谐振腔满足相位匹配条件时均匀层和相位匹配层的厚度.     

渐变带隙结构在Ⅲ-Ⅴ族太阳电池中的应用

在分析半导体带隙的渐变结构理论的基础上,研究了具有渐变带隙结构太阳电池的普遍规律和特点,采用AMPS软件结合相关试验参数对Ⅲ-Ⅴ族的AlxGa1-xAs类太阳电池中渐变带隙结构进行了计算模拟,并与普通电池进行了对比分析.一方面,带宽的递增或递减构成的势垒可以形成附加电场,帮助少子收集,增加少子寿命;另一方面,渐变后的带隙会影响实际光谱的吸收效率,使得总的载流子产额以及可利用部分发生变化,总结出带隙的渐变结构对载流子实际产生、收集等情况有着多方面的调制作用.     

可调能隙的光电器件结构——(AlAs)_ (n_l)/(GaAs)_(m_l)渐变周期超晶格

本文提出了一种具有渐变周期的(AlAs)_(nl)/(GaAs)_(ml)(1=1,2,…)超晶格,并采用递归方法计算了这种渐变周期超晶格的电子结构.其特点是带隙E_g在空间随(n_(?),m_(?))渐变.例如,对(AlAs)_4/(GaAs)_4(AlAs)_4、/(GaAs)_5/(AlAs)_4/(GaAs)_6/(AlAs)_4/(GaAs)_7结构,带隙由短周期一端的1.93eV变到长周期一端的1.78eV.同时导、价带边得到不同的调制,因而提高了电子与空穴电离率比值,有可能应用到作光电探测材料.     

一种探地雷达用的渐变槽线加载天线

提出了一种可用于探地雷达系统的电阻加载渐变槽线天线。在分析影响渐变槽线天线加载效果凼素的基础上，提出了一种改进的槽线金属面形状，提高了电阻加载的效果。实际测试结果显示，电阻加载渐变槽线天线拖尾脉冲的幅度非常低。     

多光纤点光源干涉法制作光子晶体的研究

利用多光纤点光源全息干涉法对四光纤（4+1）和五光纤（5+1）的干涉场进行理论模拟和实验测量,并比较了中心光束对整个干涉场的影响,研究表明中心光束只对干涉场对比度有影响,而不影响干涉晶格结构。同时给出了多光纤干涉的实验结果,从实验结果看出,实验和理论有比较好的一致性。并且设计了四根光纤干涉形成的渐变型光子晶体结构,对其光场的分束和聚焦作用进行了理论模拟。本文的研究为制作渐变型光子晶体分束器和聚焦透镜提供了很好的理论和实验依据。     

Wavelength shift of selectively oxidized Al/sub x/O/sub y/-AlGaAs-GaAs distributed Bragg reflectors

The effect of multiple oxidations on Al/sub x/O/sub y/-GaAs DBRs and Al/sub x/O/sub y/-AlGaAs-GaAs DBRs is investigated. With a compositionally graded AlGaAs layer, the oxide DBR remains stable under thermal stress, whereas without it, the DBR fractures. The stopband of the oxide DBR with the AlGaAs layer shifts when sequenced through multiple oxidation processes, which is attributed to the vertical oxidation of the AlGaAs. The resonance wavelength of a Fabry-Perot cavity containing an oxide DBR shifts 6 nm after 30 min of additional oxidation at 425/spl deg/C.     

一种新型高增益、低噪声980nm微腔半导体光放大器的数值分析

提出了一种新型微腔半导体光放大器结构,该半导体放大器在普通行波光放大器的波导结构上引入了上下布拉格反射镜,并在波导前后两侧的上端面上分别刻蚀出入射和出射光学窗口,其上蒸镀增透膜层.信号光以一定的倾角斜入射到波导中,以之字型路线沿波导传播.提出了一个完整的、考虑了微腔特性的稳态模型,系统模拟了微腔半导体光放大器的特性.结果表明该微腔半导体光放大器的光纤到光纤增益可达40dB,而噪声指数只有3.5dB.     

VCSEL中布拉格反射体的电流机制和伏安特性

采用张弛法数值求解静电势的泊松方程 ,得出垂直腔面发射激光器 (VCSEL)中 N型和 P型分布布拉格反射体 (DBR)中一个周期单元的精确能带图。并以此为依据 ,从理论上分别分析和比较了多子漂移扩散、纯漂移和热电子发射电流机制所起的作用。指出由一对反对称同型异质结构成的 DBR一个周期单元总是表现出欧姆性 ,但热电子发射电流机制的存在容易使每个结呈现整流特性 ,以致在电流输运过程中起主要作用的是其反向特性 ,导致偏压和电阻过大器件不能正常工作。但是漂移扩散机制具有明显欧姆性 ,在利用缓变 DBR结构消除异质尖峰势垒之后漂移扩散机制将决定主要的电流输运     

Deep-etched distributed Bragg reflector lasers with curved mirrors.Experiments and modeling

A semiconductor laser with deep-etched distributed Bragg reflectors (DBRs) supporting a planar Gaussian mode has been experimentally and theoretically studied. A 90-μm-long laser with two-groove DBRs has a low threshold current of 7 mA and a maximum side mode suppression of 17.6 dB under continuous operation. The laser resonator supports a mode that closely resembles the desired planar Gaussian mode. The reflectivities of the deep-etched DBRs were experimentally determined using broad area devices, and the reflection, transmission, and scattering properties of the DBRs were simulated using a finite-difference time-domain model. The simulations show that deep grooves, covering the full transverse extent of the guided mode, are needed to maximize the reflectivity and to minimize the scattering loss. A beam-propagation model was used to simulate the laser resonator. The simulations (as well as the experiments) show that the laser is sensitive to thermal effects. Thermal lensing narrows the mode waist, and therefore increases the spatial hole burning in the center of the resonator where the intensity is at its maximum. At high drive currents, this leads to a degradation of the spatial mode quality. The simulations also indicate that a laser with optimized DBRs (one one- and one two-groove DBRs with an etch depth of 1 μm) would have a threshold current less than 2 mA and support a high-quality planar Gaussian mode to an output power of 9 mW under continuous operation     

Fully Solution‐Processed Photonic Structures from Inorganic/Organic Molecular Hybrid Materials and Commodity Polymers

Managing the interference effects from thin (multi‐)layers allows for the control of the optical transmittance/reflectance of widely used and technologically significant structures such as antireflection coatings (ARCs) and distributed Bragg reflectors (DBRs). These rely on the destructive/constructive interference between incident, reflected, and transmitted radiation. While known for over a century and having been extremely well investigated, the emergence of printable and large‐area electronics brings a new emphasis: the development of materials capable of transferring well‐established ideas to a solution‐based production. Here, demonstrated is the solution‐fabrication of ARCs and DBRs utilizing alternating layers of commodity plastics and recently developed organic/inorganic hybrid materials comprised of poly(vinyl alcohol) (PVAl), cross‐linked with titanium oxide hydrates. Dip‐coated ARCs exhibit an 88% reduction in reflectance across the visible compared to uncoated glass, and fully solution‐coated DBRs provide a reflection of >99% across a 100 nm spectral band in the visible region. Detailed comparisons with transfermatrix methods (TMM) highlight their excellent optical quality including extremely low optical losses. Beneficially, when exposed to elevated temperatures, the hybrid material can display a notable, reproducible, and irreversible change in refractive index and film thickness while maintaining excellent optical performance allowing postdeposition tuning, e.g., for thermo‐responsive applications, including security features and product‐storage environment monitoring.     

A simple method of mesa fabrication on DBR containing heterostructures

We describe a very simple procedure of mesa fabrication on A1As/GaAs DBRs with heterostructures by wet etching using non-selective solvent. There are in general two approaches to the wet etching, a selective and non-selective one. The selective etching technique can however be used only to produce DBRs of the simplest construction i.e., DBRs that consist of only relatively thick layers of GaAs and AlAs. In realistic device heterostructures, the AlAs/GaAs DBR contains also a number of additional layers. Depending on the specific construction the thickness of these additional layers and can vary from several tenths of nanometers, as in step-like grading to single tenths of nanometers as in digital alloy grading approach. We demonstrate such DBRs, which consist of very thin layers and can be precisely etched by the non-selective etch solutions. In the etching experiments we used a number of MBE grown heterostructures consisting of DBRs of the different AlAs/GaAs interfaces construction. They were abrupt, step and digital alloy graded type. All those structures were subjected to etching in a specially designed mix of two solvents: first sulphuric acid/hydrogen peroxide/water (H₂SO₄:H₂O₂:H₂O) at the volume ratio of 8:1:1, and second citric acid/water (C₆H₈O₇:H₂O) at the ratio 1:1. Taking the advantage of the periodicity of the DBR, the etch depth control was realised by simply counting the changes in surface colours. During the etching, the decreasing thickness of the most top layers caused the change in the ambient light reflectivity. This manifests in the periodic change of the wafer colour: from the reddish to the greenish. When whole DBR is etched away the wafer surface becomes silver grey. The etching depth is controled with a precision better then the single quarter wavelength layer.     

X-Ray diffraction analysis of bandgap-engineered distributed bragg reflectors

Compositionally graded interfaces between constitutive layers of the distributed Bragg reflectors (DBRs) in vertical cavity surface emitting lasers (VCSELs) greatly reduce operating voltages. In this paper, we demonstrate the use of high-resolution x-ray diffraction (HRXRD) in the characterization of a bandgap-engineered DBR. The final structure of the DBR is determined by comparing the Bragg peak intensities and locations in the x-ray rocking curve measurements with those of dynamical x-ray diffraction simulations. The aluminum concentration of the graded interface region is determined as a function of distance to within 2%. The width of the interface is accurate to within 1.5 nm. Such sensitivity demonstrates the utility of the non-invasive x-ray technique in characterizing not only the DBR, but also the entire VCSEL structure.     

Graded Heterojunction of AlGaInP High-brightness Light Emitting Diodes

A simple model of the graded heterojunction in AlGaInP compound semiconductors was introduced to analyze the band profile. The band profiles are analyzed with the different grading ways but the same grading length and under the different doping densities. The effect of the different grading lengths on the surplus of the potential of the spike to the potential of N region are also analyzed under the different doping densities.Through the experiments,it proves that the performances of high brightness light emitting diodes can be improved by the effects of the graded heterojunction.     

Graded Heterojunction of AIGalnP High-brightness Light Emitting Diodes

A simple model of the graded heterojunction in AIGalnP compound semiconductors was introduced to analyze the band profile. The band profiles are analyzed with the different grading ways but the same grading length and under the different doping densities. The effect of the different grading lengths on the surplus of the potential of the spike to the potential of N region are also analyzed under the different doping densities. Through the experiments, it proves that the performances of high brightness light emitting diodes can be improved by the effects of the graded heterojunction.     

AlGaAs/GaAs/AlGaAs渐变异质结光致发光仿真研究

分析了AlGaAs/GaAs/AlGaAs渐变异质结的光致发光特性。根据理论及仿真结果,确定了GaAs发光的最优能带结构为双异质结P-AlGaAs/P-GaAs/P-AlGaAs或者N-AlGaAs/N-GaAs/ N-AlGaAs,并且异质结两边能带渐变。基于所选结构,研究了能带渐变及层宽对发光效率的影响。研究结果表明,外体区吸收层的能带渐变,且外体区激发层的能带不变,发光区域的载流子最多,发光能量值最大。激励光源的波长不同,各层有不同的最优宽度,为器件的整体优化提供了依据。AlGaAs/GaAs/AlGaAs渐变异质结的光致发光研究为高效率器件如太阳电池、发光二极管等的实用化设计、研制提供了有价值的参考。