R面、C面蓝宝石上生长的InGaN多层量子点的发光性质研究

采用表面钝化和MOCVD低温生长在蓝宝石(0001)面(即C面)和蓝宝石(1102)面(即R面)上形成了InGaN量子点,并构成了该量子点的多层结构.原子力显微镜测试的结果表明单层InGaN量子点平均宽约40nm,高约15nm;而多层量子点上层的量子点则比单层的InGaN量子点大.R面蓝宝石衬底上生长的InGaN量子点和C面蓝宝石衬底上生长的InGaN量子点相比,其PL谱不仅强度高,而且没有多峰结构.这是由于在C面蓝宝石衬底上生长的InGaN/GaN多层量子点沿生长方向[0001]存在较强的内建电场,而在R面蓝宝石衬底上得到的多层量子点沿着生长方向[1120]没有内建电场.InGaN量子点变温光致发光(PL)谱研究发现量子点相关的峰有快速红移现象,这是量子点系统所特有的PL谱特征.用在R面蓝宝石上生长的InGaN量子点作有源层有望避免内建电场的影响,得到高量子效率且发光波长稳定的发光器件.     

N型掺杂ZnSe/BeTeⅡ型量子阱中空间间接带电激子跃迁发光的直接证据

本文研究了N型掺杂ZnSe/BeTe/ZnSeⅡ型量子阱空间间接发光谱的外加电场依赖性.实验结果表明,其发光谱只显示了一个线性偏振度较低的发光峰.这是由于掺杂电子屏蔽了Ⅱ型量子阱中的内秉电场,并使得两个ZnSe阱层具有相同的势.同时该发光谱具有反玻耳兹曼(inverse-Boltzmann)分布,并且线型和线性偏振度在...     

TMIn流量对GaN基蓝光LED外延薄膜的影响

以蓝宝石(Al2O3)为衬底,采用有机金属化学气相沉积(MOCVD)技术生长InGaN/GaN多量子阱结构.本文通过调整外延生长过程中三甲基铟(TMIn)流量,研究了TMIn流量对InGaN/GaN多量子阱结构的合金组分、晶体质量和光学性质的影响.本文采用高分辨X射线衍射(HRXRD)、原子力显微镜(AFM)和光致发光(PL)测试表征其结构和光学性质.HRXRD测试结果表明,随TMIn流量增加,"0"级峰与GaN峰之间角偏离增大,更多的In并入薄膜中.HRXRD与AFM表征结果表明:增大TMIn流量会导致外延薄膜中的位错密度增大,V形坑数量增加,晶体质量严重恶化;PL测试结果表明,随着TMIn流量增加,发光强度逐渐降低,半高宽增大,这是由于晶体质量恶化所导致.因此严格控制铟源流量对于改善量子阱薄膜的晶体质量与光学性质有着至关重要的作用.     

低温AlN插入层的生长温度对AlGaN/GaN量子阱应力弛豫作用的影响

利用高分辨X射线衍射仪(HRXRD)及原子力显微镜(AFM)研究了低温AlN插入层的生长温度对AlGaN/GaN量子阱应力弛豫作用的影响.结果表明,低温AlN插入层不同的生长温度会导致AlGaN/GaN量子阱不同的表面粗糙度及穿透位错密度,并且当生长温度达到640℃时样品中表面粗糙度及穿透位错密度达到最低,同时具有最高的载流子迁移率及带边发光峰强度.在不同的生长温度,低温AlN表面具有不同的表面形貌.不同的表面形貌将直接影响界面处位错主滑移系的开动及位错阻挡机制.通过分析可以得知,低温AlN不同的表面形貌是由于Al原子在不同温度下的不同的迁移机制造成.     

激发功率密度和阱层厚度对极化InGaN/GaN多量子阱光致发光性能的影响

用MOCVD技术在c面蓝宝石衬底上生长了具有不同阱层厚度的InGaN/GaN多量子阱结构,研究了阱层厚度和激发功率密度对多量子阱光致发光(PL)性能的影响.结果表明,随着激发功率密度的增加,PL的峰值波长会出现不同程度的蓝移,且阱层越厚,蓝移的越明显.PL的峰值波长随着激发功率密度和阱厚的变化关系可以用光生载流子对极化场的屏蔽效应和带隙填充效应来解释.阱最薄的样品(1.8 nm)由于其极化效应最弱,电致发光谱具有最高的发光强度,但其发光波长较短仅有430 nm.     

δ掺杂Si对InAs/GaAs量子点太阳电池的影响

在InAs/GaAs量子点的自组装生长阶段,采用δ掺杂技术对量子点进行不同浓度的Si掺杂,可以使得量子点的室温光致发光峰强度大幅提高,其原因是掺杂的Si原子释放电子钝化了周围的非辐射复合中心.这种掺杂也应用到了量子点太阳电池中,结果表明电池开路电压从0.72 V提高到了0.86 V,填充因子从60.4;提高到73.2;,短路电流从26.9 mA/cm2增加到27.4 mA/cm2.优化的Si掺杂可将量子点太阳的电池效率从11.7;提升到17.26;.     

半导体GaAs—Ga0.65Al0.35As多量子阱的光谱性质及实现激光制冷的可能

我们利用光致发光(PL)和激发光谱(PLE)技术研究了GaAs量子阱的光谱性质,在GaAs量子阱的光致发光中观察到上转换发光,首次提出GaAs量子阱结构可能实现激光制冷,探索了GaAs量子阱结构的发光机理。     

生长温度对InAs/GaAs量子点太阳电池的影响研究

InAs/GaAs量子点的生长形貌和特性受不同生长环境和生长条件影响.本文借助光致发光光谱(PL)特性表征方法,通过实验生长,对比研究不同生长温度下获得的量子点性能,结合当前三结叠层GaInP/GaAs/C-e(2-terminal)电池存在的问题,以及该电池的设计、制作要求,分析了InAs量子点的不同生长温度对于具有量子点结构的中电池吸收的影响.     

二次退火制备Ⅲ-Ⅴ族半导体量子点

利用离子注入法在一块Si(001)衬底上注入了In+和As+,注入能量分别为210keV,150keV,注入剂量6.2×1016cm-2,8.6×1016cm-2,另一块Si(001)衬底上注入Ga+和Sb+,注入能量分别为140keV,220keV,注入剂量分别为8.2×1016cm-2,6.2×1016cm-2,然后对样品分别经过一次退火和二次退火处理制备出了Si基量子点材料。用透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)观察了退火后量子点截面像,用PL探测量子点的光致发光谱,发现经二次退火生长的量子点微晶格结构和Si衬底损伤的修复均明显优于一次退火。     

半导体所在纳米线量子结构材料研究方面取得新进展

<正>中国科学院半导体研究所超晶格国家重点实验室研究员牛智川课题组近年来深入系统地研究了In(Ga)As量子点、量子环、纳米线中量子点、纳米线中量子环的自组织外延生长、液滴外延生长方法。最近,课题组查国伟、喻颖等在研究中发现:通过优化GaAs纳米线侧壁淀积Ga液滴成核温度与晶化条件等参数,可以生长出密度与形貌可控量子点、量子环等新奇量子结构,首次发现单根纳米线侧壁形成单个"方形"量子环且具有高品质发光特性。(Nanoscale,10.1039(2013))。他们进一步生长了GaAs/AlGaAs纳米线中的GaAs量子点,以及置于AlGaAs量子环中心并覆盖AlGaAs     

Growth of strain-compensated GaInNAs/GaAsP quantum wells for 1.3 μm lasers

Strain-compensated GaInNAs/GaAsP quantum well structures and lasers were grown by gas source molecular beam epitaxy using a RF-plasma nitrogen radical beam source. The optimal growth condition for the quantum well structure was determined based on room-temperature photoluminescence measurements. Effects of rapid thermal annealing (RTA) on the optical properties of GaInNAs/GaAsP quantum well structures as well as laser diodes are examined. It was found to significantly increase the photoluminescence from the quantum wells and reduce the threshold current density of the lasers, due to a removal of N induced nonradiative centers from GaInNAs wells.     

Effects of barrier growth temperature on the properties of InGaN/GaN multi-quantum wells

The effects of the growth temperature and ambient of GaN quantum barriers on the characteristics of InGaN/GaN multi-quantum wells (MQWs) grown by a thermally pre-cracked ion-supplied metalorganic chemical vapor deposition (TPIS-MOCVD) system were investigated. The improvement of optical, structural properties and surface morphology in the MQWs with increasing the growth temperature of quantum barriers was found. Without a GaN capping layer, there were many pits and the thickness of quantum pair reduced by the thermal etching during the temperature-ramping process. Photoluminescence (PL) peaks showed a blue-shift and double peaks, but relative PL intensity abruptly increased due to the suppression of deep level related defects and smooth surface morphology caused by the increased surface mobility of adatom in the high temperature region. By using a GaN capping layer on the InGaN well layer, the thermal decomposition of the InGaN well layer was suppressed and pits on the surface abruptly reduced. A hydrogen carrier gas for the GaN barrier growth also improved the optical and structural properties of MQWs.     

Temperature quenching mechanisms for photoluminescence of MBE-grown chlorine-doped ZnSe epilayers

We report on a detailed investigation on the temperature-dependent behavior of photoluminescence from molecular beam epitaxy (MBE)-grown chlorine-doped ZnSe epilayers. The overwhelming neutral donor bound exciton (Cl⁰X) emission at 2.797 eV near the band edge with a full-width at half-maximum (FWHM) of 13 meV reveals the high crystalline quality of the samples used. In our experiments, the quick quenching of the Cl⁰X line above 200 K is mainly due to the presence of a nonradiative center with a thermal activation energy of 90 meV. The same activation energy and similar quenching tendency of the Cl⁰X line and the I₃ line at 2.713 eV indicate that they originate from the same physical mechanism. We demonstrate for the first time that the dominant decrease of the integrated intensity of the I₃ line is due to the thermal excitation of the “I₃ center”-bound excitons to its free exciton states, leaving the “I₃ centers” as efficient nonradiative centers. The optical performance of ZnSe materials is expected to be greatly improved if the density of the “I₃ center” can be controlled. The decrease in the luminescence intensity at moderately low temperature (30–200 K) of the Cl⁰X line is due to the thermal activation of neutral-donor-bound excitons (Cl⁰X) to free excitons.     

Structural and optical properties of quaternary AlInGaN epilayers grown by MOCVD with various TMGa flows

AlInGaN quaternary epilayers have been grown with various TMGa flows by metalorganic chemical vapor deposition to investigate the influence of growth rate on the structural and optical properties. Triple-axis X-ray diffraction measurements show AlInGaN epilayers have good crystalline quality. Photoluminescence (PL) measurements show that the emission intensity of AlInGaN epilayers is twenty times stronger than that of AlGaN epilayer with comparable Al content. V-shaped pits are observed at the surface of AlInGaN epilayers by atomic force microscopy (AFM) and transmission electron microscopy (TEM). High growth rate leads to increased density and size of V-shaped pits, but crystalline quality is not degraded.     

CuInS2量子点敏化ZnO基光阳极的制备与性能研究

采用两步法在导电玻璃(FTO)基板上制备纯氧化锌(ZnO)纳米棒和钇掺杂的氧化锌(ZnO∶Y)纳米棒,采用连续离子层吸附反应法(SILAR)在所制备的ZnO及ZnO∶Y纳米棒上沉积CuInS₂量子点制备ZnO/CuInS₂和ZnO∶Y/CuInS₂光阳极。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、电子探针能谱仪(EDS)、紫外-可见分光光度计(UV-Vis)、电流密度-电压(J-V)曲线等技术手段对不同光阳极样品的晶相结构、微观形貌、化学组成、光吸收性能和太阳电池性能进行了表征。实验结果表明:所制备的ZnO纳米棒和ZnO∶Y纳米棒为六方纤锌矿结构。CuInS₂量子点敏化的ZnO纳米棒薄膜的光学带隙从3.22 eV减小为2.98 eV。CuInS₂量子点敏化ZnO∶Y太阳能电池的短路电流密度和光电转换效率比未掺杂的ZnO纳米棒组装的太阳能电池分别提高了6.5%和50.4%。     

Interactions between inversion domains and InGaN/GaN multiple quantum wells investigated by transmission electron microscopy

The propagation properties of inversion domains (IDs) in InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition have been investigated by transmission electron microscopy (TEM). The majority of the IDs, originating from the sapphire and/or buffer layer, propagate through the MQWs with normal wurtzite structure retaining their original structural features. Some of IDs could induce V-shaped pits in the MQW structures proposing a new formation mechanism for the so-called V-shaped defects. Detailed measurements show that a few IDs are found to be stopped in abnormal MQW regions, where In droplets appear due to phase separation. We presented direct evidence of pure In-phase droplets by means of high-resolution TEM. The above results provide new information on the structural defects in InGaN/GaN-based materials.     

SiW12、CsPbI3协同提高TiO2纳米管光电转换效率的研究

为克服TiO₂纳米管在光电转换时电子-空穴复合率高和吸收光谱范围窄的缺陷,利用多酸H₄SiW₁₂O₄₀(SiW₁₂)和CsPbI₃量子点对其协同修饰,采用电沉积法将SiW₁₂沉积在TiO₂纳米管上,制备了SiW₁₂/TiO₂纳米管复合薄膜;使用高温热注射法合成出CsPbI₃量子点,再通过化学浴沉积法沉积CsPbI₃量子点到复合薄膜上,得到SiW₁₂/CsPbI₃/TiO₂纳米管复合薄膜,探究SiW₁₂沉积时间、CsPbI₃沉积次数对TiO₂纳米管光电性能的影响。利用扫描电子显微镜(SEM)、能谱仪(EDS)、透射电子显微镜(TEM)、X射线衍射(XRD)仪、红外分光光度计(FT-IR)、紫外-可见分光光度计(UV-Vis)对薄膜进行表征,使用电化学工作站测试薄膜的光电化学性能。结果表明:TiO₂纳米管沉积多酸SiW₁₂和CsPbI₃量子点后,光吸收范围扩大、电荷转移电阻降低,光电转换效率得到显著提升,最高达到0.52%。说明SiW₁₂和CsPbI₃的协同作用很好地抑制了TiO₂纳米管电子-空穴的复合,并拓宽了吸收光谱范围,提高了TiO₂纳米管的光电转换效率。     

Control of the morphology of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition

Various techniques for morphological evolution of InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition have been evaluated. Atomic force microscopy, photoluminescence (PL) and X-ray diffraction measurements have been used for characterization. It is shown that inclusions, that are generated into the V-defects in the InGaN quantum wells (QW), can be removed by introducing a small amount of hydrogen during the growth of GaN barriers. This hydrogen treatment results in partial loss of indium from the QWs, but smooth surface morphology of the MQW structure and improved optical quality of InGaN wells are obtained. The density of the V-defects could be reduced by reducing the dislocation density of the underlying GaN buffer.     

Optical property of self-assembled GaInNAs quantum dots grown by solid source molecular beam epitaxy

Self-assembled GaInNAs/GaAs quantum dots (QDs) are promising structures for extending the emission wavelength of GaInNAs/GaAs quantum wells from 1.3 to 1.55 μm and beyond. We report herein the growth of GaInNAs/GaAs quantum dot samples of different deposited thickness by solid source molecular beam epitaxy using active nitrogen radicals generated by a radio frequency nitrogen plasma source. Images from atomic force spectroscopy reveal the increase of non-uniformity QDs size following the increase in the deposited thickness. Temperature-dependent photoluminescence (PL) measurements show PL line width shrinkage at low temperature suggests the relaxation of carriers into neighboring QD local-energy minimum. The low thermal activation energy of ∼72 meV, estimated from the temperature-dependent integrated PL intensity curve suggests the existence of non-radiative recombination centers that quench the luminescence intensity at higher temperature.