光电耦合对InGaN/GaN量子阱光学性能的影响

围绕高性能GaN基垂直腔面发射激光器(VCSELs),设计了两种具有不同光电耦合强度的InGaN/GaN量子阱(QWs)样品,研究了它们的光学性质。样品A在腔模的两个波腹处各放置两个InGaN耦合量子阱,而样品B在腔模的一个波腹处放置5个InGaN耦合量子阱。计算表明样品A具有较大的相对光限制因子1.79,而样品B为1.47。光学测试发现样品A有着更高的内量子效率(IQE)和更高的辐射复合效率。使用两种样品制作了光泵VCSEL结构,在光激发下实现激射,其中基于样品A的VCSEL有着更低的激射阈值。结果表明有源区结构会显著影响量子阱与光场的耦合作用、外延片的内量子效率、辐射复合寿命和VCSEL激射阈值,同时也说明样品A的有源区结构更有利于制作低阈值的VCSEL器件。     

GaN垂直腔面发射激光器研究进展

氮化镓(GaN)垂直腔面发射激光器(VCSEL)在近20年来获得了飞速发展,已成为下一代半导体激光器的研究热点。GaN是制造从紫外波段到绿色波段光电子器件的绝佳材料,而VCSEL具有阈值和发散角小、调制速率高,以及输出光束呈圆对称等特点。首先回顾了基于GaN的VCSEL的发展历史,简要介绍了它的主要应用方向;然后讨论了反射镜与谐振腔设计与制造中的关键问题;接着分析了三种不同结构的GaN VCSEL的散热机理,并分析讨论了优化散热的策略;最后介绍了基于GaN的蓝色、绿色和紫外VCSEL的研究进展及最新思路。     

Silica-based microcavity fabricated by wet etching

Silica whispering gallery mode(WGM) microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10~4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.     

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells

The structural and optical properties of InGaN/GaN multiple quantum wells(MQWs) with different barrier thicknesses are studied by means of high resolution X-ray diffraction(HRXRD), a cross-sectional transmission electron microscope(TEM), and temperature-dependent photoluminescence(PL) measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodicity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization potentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence,and the corresponding activation energy(or the localization potential) increases with the increase of the barrier thickness.The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers,i.e., clusters with lower In contents aggregate into clusters with higher In contents.     

激光剥离GaN表面的抛光技术

激光剥离(LLO)技术是研制新型氮化镓(GaN)基谐振腔结构光电子器件的关键技术。然而LLO后的GaN表面往往具有较大的粗糙度,而制作谐振腔结构器件需要很高的表面平整度,因此需要对LLO后的GaN表面进行抛光。分别采用金刚石粉抛光液和胶粒二氧化硅抛光液进行机械抛光和化学机械抛光(CMP),并对比了两种方法获得的抛光结果,研究发现前者会在抛光后的GaN表面引入划痕,而采用后者可以得到亚纳米级平整度的表面。进一步的实验结果表明,胶粒二氧化硅抛光液同样适用于图形化衬底外延片激光剥离后的GaN表面抛光。     

垂直结构GaN基LED用Ni/Ag反射镜电极

Ni/Ag/Ti/Au金属系反射镜电极广泛用于GaN基垂直结构发光二极管(LED)的传统制造工艺.这种电极需要进行高温长时间整体退火才能获得高质量的欧姆接触,但对电极的反射率和器件性能影响较大.介绍了一种新工艺方法,该方法将电极分解为接触层和反射层,降低反射层经历的退火温度和时间,获得了拥有良好的欧姆接触特性和高反射率的反射镜电极,解决了传统电极光学性能和电学性能相互制约的问题.首先生长极薄的Ni/Ag作为接触层,对接触层进行高温长时间退火后再生长厚层Ag作为反射层,之后再进行一次低温退火.使得对反射起主要作用的反射层免于高温长时间退火,相较于传统Ni/Ag/Ti/Au电极,该方法在获得更优良的欧姆接触的同时,提升了电极的反射率.在氧气氛围下进行500℃接触层退火3 min,400℃整体退火1 min后,电极的比接触电阻率为1.7×l0-3Ω·cm2,同时在450 nm处反射率为93％.     

InGaN/GaN多量子阱太阳电池的研制及特性研究

利用金属有机物化学气相沉积技术在蓝宝石衬底上生长了InGaN/GaN多量子阱外延结构,高分辨率X射线衍射测量结果显示,量子阱结构界面清晰,周期重复性很好,InGaN阱层的In组分约为0.2。利用该外延结构制备的InGaN/GaN多量子阱太阳电池的开路电压为2.16V,转换效率达到了0.64%。器件的I-V测量结果显示,在光照条件下,曲线的正向区域存在一明显的"拐点"。随着聚光度的减小,I-V曲线的"拐点"逐渐向高电压区域移动,同时器件的开路电压也随之急剧下降。通过与理论计算对比,发现器件开路电压的下降幅度明显大于理论计算值。进一步分析表明,InGaN量子阱的极化效应不仅是I-V曲线产生拐点以及器件开路电压下降过快的主要原因,也是影响氮化物太阳电池性能的关键因素之一。     

中红外硅微透镜阵列的离焦效应

本文采用严格数值算法对中红外硅微透镜阵列进行了模拟,该微透镜阵列特征尺寸小于波长工作波长。研究发现该微透镜阵列存在一个显著的离焦效应,其离焦量达到0.4左右,超出了现有的传统理论模型预测范围。对微透镜阵列进行了制作和焦距测试,发现测试结果跟数值模拟基本吻合。微纳衍射光学集成系统中透镜离焦量是系统集成非常重要的一个参数,该研究结果为硅微透镜阵列和中红外探测器光学集成提供有效参考。