基于介质超表面的宽谱、大偏转角近红外光束偏转器

设计了一种适合集成的基于介质超表面的透射式光束偏转器,可在1550 nm附近的红外波段实现大角度偏转,同时具有宽光谱、高效率的优势。根据广义斯涅尔定律设计并优化了光束偏转器的结构,由横截面为梯形的非晶硅纳米柱周期性排列在石英玻璃衬底上构成,相比于传统超表面采用多个纳米柱实现离散的相位梯度,梯形纳米柱形成的连续相位梯度可以获得更好的偏转特性。利用时域有限差分算法对光束偏转器的效率、偏转角、宽光谱和入射角度依赖性等性能进行了仿真分析,采用电子束光刻等工艺制备加工出上述器件并进行了测试。仿真结果表明偏转器在1350~1650 nm波段均具备良好的偏转特性,平均透射率高于87%,平均偏转率为81%;器件在1550 nm处实现了42.8°的大偏转角,透射率为84%,偏转率为80%,且允许入射角度在-10°~5°变化。实验测试结果表明对于1550 nm波长,光束偏转角度在41°附近,器件透射率约为76%,约35%的入射光偏转到目标角度。上述方案为近红外超表面器件的设计提供了新的思路,实现了效率、偏转角和适用波长的优化,透射式光路更加适合集成,应用潜力更大。

Efficiency Droop Effect Mechanism in an InGaN/GaN Blue MQW LED

In order to clarify the origin of the efficiency droop effect in InGaN based blue multiple-quantum-well(MQW)light emitting diodes(LEDs),a reasonable model is set up,taking all the possible factor(carrier delocalization,carrier leakage and Auger recombination)into account.By fitting the external quantum efficiency-injection current(η–Ⅰ)measurements of two LED samples,the validity of the model is demonstrated.The fit results show that the main origin of efficiency droop at a high injection current is carrier leakage.Furthermore it is also indicated that carrier delocalization plays an important role in the efficiency droop effect in those LEDs of large localization degree.

A GaN p-i-p-i-n Ultraviolet Avalanche Photodiode

A separated absorption and multiplication GaN p–i–p–i–n avalanche photo-diode(APD)with a 25μm diameter mesa is proposed and demonstrated.Compared to the conventional p–i–n APD,the p–i–p–i–n structure reduces the probability of premature micro-plasma breakdown,raises the gain from 30 to 400 and reduces the work voltage from 93 to 48 V.The temperature test is set on p–i–p–i–n APDs,and the positive coefficient of 30 mV/K shows that avalanche breakdown happens in the devices.The peak responsivity of p–i–p–i–n APDs is 0.11 A/W under a wavelength of 358 nm.

Photocatalysis of InGaN Nanodots Responsive to Visible Light

Photocatalysis of InGaN nanodots grown on GaN/sapphire templates by metal organic vapor phase epitaxy is studied.Photodegradation of methylene orange by InGaN nanodots responsive to visible light is observed.Analysis through atomic force microscopy and time-resolved photoluminescence measurements show that wider bandgap of InGaN,larger specific surface area and more proportion of photocarriers diffusing to the surface before recombination are propitious to photodegradation.

Density Increase of Upper Quantum Dots in Dual InGaN Quantum-Dot Layers

Single and dual layers of InGaN quantum dots(QDs)are grown by metal organic chemical vapor deposition.In the former,the density,average height and diameter of QDs are 1.3×10^(9) cm^(−2),0.93 nm and 65.1 nm,respectively.The latter is grown under the same conditions and possesses a 20 nm low-temperature grown GaN barrier between two layers.The density,average height and diameter of QDs in the upper layer are 2.6×10^(10) cm^(−2),4.6 nm and 81.3 nm,respectively.Two reasons are proposed to explain the QD density increase in the upper layer.First,the strain accumulation in the upper layer is higher,leading to a stronger three-dimensional growth.Second,the GaN barrier beneath the upper layer is so rough it induces growth QDs.

基于半导体MZ调制器与DFB激光器混合集成的小型化光发射模块的设计与研究

针对半导体DFB激光器、铌酸锂MZ调制器采用分立封装形式且整体尺寸较大的问题,采用半导体MZ调制器和DFB激光器两类芯片并进行混合集成封装有望显著减小模块的整体尺寸。论文根据芯片和模块尺寸要求提出了一个整体布局结构,并选用双透镜加隔离器以及锥形透镜光纤光耦合方案和微带线转GCPW微波耦合方案。通过仿真计算,对模块中激光器与调制器混合集成设计的关键参数及容差进行了研究。本混合集成发射模块在尺寸结构小型化的同时,也可确保自身良好的稳定性与可靠性。