Controlled Nucleation of GaN Nanowires Grown with Molecular Beam Epitaxy

The location of GaN nanowires is controlled with essentially perfect selectivity using patterned SiN_x prior to molecular beam epitaxy growth. Nanowire growth is uniform within mask openings and absent on the mask surface for over 95% of the usable area of a 76 mm diameter substrate. The diameters of the resulting nanowires are controlled by the size of the mask openings. Openings of approximately 500 nm or less produce single nanowires with symmetrically faceted tips.     

砷化镓纳米线在非晶玻璃衬底生长和特性研究

The growth of GaAs nanowires directly on fused quartz substrates using molecular beam epitaxy via a vapor-liquid-solid mechanism with gold as catalyst is reported. Unlike conventional Au-catalyst MBE growth of nanowires （NWs） on GaAs substrates, zinc blende is found to be the dominant crystal structure for NWs grown on fused-quartz substrates by MBE. Further transmission electron microscopy measurements show that the prepared ZB NWs have the growth direction of [112] and lamellar { 111 } twins extend through the length of NWs. Although there are longitudinal planar defects that extend through NWs, the narrow full width at half maximum of PL implies high crystal quality of NWs grown on fused-quartz substrates.     

X-Ray Diffraction and Photoluminescence Studies of InN Grown by Plasma-Assisted Molecular Beam Epitaxy with Low Free-Carrier Concentration

We report studies of InN grown by plasma-assisted molecular beam epitaxy. GaN templates were first grown on sapphire substrates followed by InN overgrown at 457°C to 487°C. Atomic force microscopy shows the best layers to exhibit step-flow growth mode of the InN, with a root-mean-square roughness of 0.7 nm for the 2 μm × 2 μm scan and 1.4 nm for the 5 μm × 5 μm scan.␣Measurements of the terrace edges indicate a step height of 0.28 nm. Hall measurements at room temperature give mobilities ranging from 1024 cm²/V s to 1904 cm²/V s and the electron concentrations are in the range of 5.9 × 10¹⁷ cm⁻³ to 4.2 × 10¹⁸ cm⁻³. Symmetric and asymmetric reflection x-ray diffraction measurements were performed to obtain lattice constants a␣and c. The corresponding hydrostatic and biaxial stresses are found to range from −0.08 GPa to −0.29 GPa, and −0.05 GPa to −0.32 GPa, respectively. Low-temperature photoluminescence peak energies range from 0.67 eV to 0.70 eV, depending on residual biaxial stress, hydrostatic pressure, and electron concentrations. The electron concentration dependence of the estimated Fermi level is analyzed using Kane’s two-band model and conduction-band renormalization effects.     

氧化锡纳米线的光致发光性能分析

通过热蒸发沉积法在常压、900°C高温条件下,合成了氧化锡纳米线结构。利用扫描电子显微镜、透射电子显微镜及选区电子衍射对样品的表面形貌和微结构进行了表征,X射线衍射、傅里叶变换红外光谱进一步证明所制纳米结构为金红石型氧化锡单晶结构。在77K和300K温度条件下,研究了所制氧化锡纳米线及其在氧气气氛中退火后的光致发光性能。     

Novel Type‐II InAs/AlSb Core–Shell Nanowires and Their Enhanced Negative Photocurrent for Efficient Photodetection

The control of optical and transport properties of semiconductor heterostructures is crucial for engineering new nanoscale photonic and electrical devices with diverse functions. Core–shell nanowires are evident examples of how tailoring the structure, i.e., the shell layer, plays a key role in the device performance. However, III–V semiconductors bandgap tuning has not yet been fully explored in nanowires. Here, a novel InAs/AlSb core–shell nanowire heterostructure is reported grown by molecular beam epitaxy and its application for room temperature infrared photodetection. The core–shell nanowires are dislocation‐free with small chemical intermixing at the interfaces. They also exhibit remarkable radiative emission efficiency, which is attributed to efficient surface passivation and quantum confinement induced by the shell. A high‐performance core–shell nanowire phototransistor is also demonstrated with negative photoresponse. In comparison with simple InAs nanowire phototransistor, the core–shell nanowire phototransistor has a dark current two orders of magnitude smaller and a sixfold improvement in photocurrent signal‐to‐noise ratio. The main factors for the improved photodetector performance are the surface passivation, the oxide in the AlSb shell and the type‐II bandgap alignment. The study demonstrates the potential of type‐II core–shell nanowires for the next generation of photodetectors on silicon.     

Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved. RTA was carried out at 650℃ and its effect was studied by the comparising the room\|temperature PhotoLuminescence (PL) spectra for the non ion removed (grown without magnets) sample with for the ion removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion removed GaInNAs/GaAs SQW after annealing (compared with those for ion removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ion removed GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect assisted In Ga interdiffusion rather than defect assisted N As interdiffusion.     

Photoluminescence and interface abruptness in InGaAsP/InGaAsP quantum wells

Quantum well (QW) structures consisting of InGaAsP wells and InGaAsP barriers grown by gas-source molecular beam epitaxy have been examined by low temperature photoluminescence (PL) in order to evaluate the contributions of compositional fluctuations in the quaternary alloy and of interface roughness to the PL linewidth. The well material was InGaAsP with a bandgap corresponding to a wavelength of 1.3 μm and the barrier material was InGaAsP of 1.15 μm. The theory for QW excitonic linewidths as a function of well thickness L_z due to fluctuations in alloy composition has been extended to include the case of the quaternary InGaAsP barrier. If the interfaces are atomically abrupt, the linewidth is dominated by compositional fluctuations in the well at large L_z and compositional fluctuations in the barrier at small L_z. The theory predicts a weak dependence of the linewidth on L_z since the composition of the well and barrier are similar. For rough heterointerfaces, the theory indicates the usual increase in linewidth with decreasing L_z. Photoluminescence measurements at 13K in arrays of single InGaAsP/InGaAsP QWs with L_z from 1.0 to 6.0 nm show only a weak variation of the full width at half maximum (FWHM) with L_z, in agreement with the theory for smooth interfaces. Furthermore, the lowest measured FWHM of 8.9 meV was found for a narrow well of L_z=1.8 nm, indicating the InGaAsP/InGaAsP interfaces are smooth and that the PL linewidth is dominated by compositional fluctuations.     

Characteristics and device applications of erbium doped III-V semiconductors grown by molecular beam epitaxy

We have studied the properties of molecular beam epitaxially (MBE)-grown Erdoped III-V semiconductors for optoelectronic applications. Optically excited Er³⁺ in insulating materials exhibits optical emission chiefly around 1.54 μm, in the range of minimum loss in silica fiber. It was thought, therefore, that an electrically pumped Er-doped semiconductor laser would find great applicability in fiber-optic communication systems. Exhaustive photoluminescence (PL) characterization was conducted on several of As-based III-V semiconductors doped with Er, on bulk as well as quantum-well structures. We did not observe any Errelated PL emission at 1.54 μm for any of the materials/structures studied, a phenomenon which renders impractical the realization of an Er-doped III-V semiconductor laser. Deep level transient spectroscopy studies were performed on GaAs and AlGaAs co-doped with Er and Si to investigate the presence of any Er-related deep levels. The lack of band-edge luminescence in the GaAs:Er films led us to perform carrier-lifetime measurements by electro-optic sampling of photoconductive transients generated in these films. We discovered lifetimes in the picosecond regime, tunable by varying the Er concentration in the films. We also found the films to be highly resistive, the resistivity increasing with increasing Er-concentration. Intensive structural characterization (double-crys-tal x-ray and transmission electron microscopy) performed by us on GaAs:Er epilayers indicates the presence of high-density nanometer-sized ErAs precipitates in MBE-grown GaAs:Er. These metallic nanoprecipitates probably form internal Schottky barriers within the GaAs matrix, which give rise to Shockley-Read-Hall recombination centers, thus accounting for both the high resistivities and the ultrashort carrier lifetimes. Optoelectronic devices fabricated included novel tunable (in terms of speed and responsivity) high-speed metal-semiconductor-metal (MSM) photodiodes made with GaAs:Er. Pseudomorphic AlGaAs/ InGaAs modulation doped field effect transistors (MODFETs) (for high-speed MSM-FET monolithically integrated optical photoreceivers) were also fabricated using a GaAs:Er buffer layer which substantially reduced backgating effects in these devices.     

Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma-assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved.RTA was carried out at 650℃ and its effect was studied by the comparising the roomtemperature PhotoLuminescence (PL) spectra for the non ion-removed (grown without magnets) sample with for the ion-removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion-removed GaInNAs/GaAs SQW after annealing (compared with those for ion-removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ionremoved GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion-removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect-assisted In-Ga interdiffusion rather than defect-assisted N-As interdiffusion.     

花状纳米结构ZnS:Cu的制备与光学性质研究

采用水热法合成了具有花状纳米结构的ZnS:Cu粉末.利用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)和荧光光谱仪研究了在不同正硅酸四乙酯(TEOS)含量的条件下制备的样品的物相、形貌与光致发光(PL)性质.测试结果表明:制备的ZnS:Cu样品都具有立方相闪锌矿结构;由于TEOS分子...     

核/壳结构ZnS:Mn/ZnS量子点光发射增强研究

利用水溶性前驱体材料在水性介质中制备了ZnS:Mn和ZnS:Mn/ZnS核/壳结构量子点(QDs,quantum dots),并用X射线衍射(XRD)、光致发光(PL)对ZnS:Mn和ZnS:Mn/ZnS核/壳结构QDs的结构和发光性能进行研究.ZnS:Mn和ZnS:Mn/ZnS QDs XRD谱与标准谱吻合,根据De...     

ZnO材料的生长及表征

氧化锌材料是新一代宽禁带光电子半导体材料和场致发射材料，通过等离子体分子束外延设备，在a-plane的蓝宝石衬底上生长了高质量的氧化锌外延材料。在生长过程中用反射高能电子束衍射仪(RHEED)，研究了生长时材料薄膜的表面形貌。为了使材料更好地应用于器件，研究了材料的掺杂性质。研究了给体束缚激子(Donor bound exeiton (DX))、自由激子(Free exciton(EX))和受体束缚激子(Aeeeptor bound exciton (AX))随温度变化的发光过程。用紫外-可见透射光谱研究了ZnO薄膜材料的透射光谱性质。结果表明，用分子束外延生长设备成功地生长了高质量的氧化锌薄膜材料。     

InP衬底上晶格匹配四元系InAlGaAs的气态源分子束外延生长

采用高分辨率X射线衍射摇摆曲线、光致发光以及霍尔测试对采用气态源分子束外延方法生长的四元系In-AlGaAs材料性质进行了表征。摇摆曲线结果表明,根据计算数据所生长的InAlGaAs样品与InP衬底基本匹配.光致发光和霍尔测试结果显示随着Al组分的增加,样品的光致发光强度、电子浓度和迁移率均有所下降.样品的三族元素组分由光致发光及X射线衍射实验获得,测试结果与设计值吻合,Al组分的实验设计值与测试结果的关系提供了一种实用的精确控制组分的方法.     

(113)B和(100)面InAs/GaAs量子点光致发光光谱特性研究

利用分子束外延技术在(100)和(113)B GaAs衬底上进行了有/无AlAs盖帽层量子点的生长,测量了其在4～100 K温度区间的PL光谱。通过对PL光谱的积分强度、峰值能量和半高宽进行分析进而研究载流子的热传输特性。无AlAs盖帽层的(113)B面量子点的PL光谱的热淬灭现象可以由载流子极易从量子点向浸润层逃逸来解释。然而,有AlAs盖帽层的(113)B量子点的PL热淬灭主要是由于载流子进入了量子点与势垒或者浸润层界面中的非辐射中心引起的。并且其PL的温度依存性与利用Varshni定律计算的体材料InAs的温度依存性吻合很好,表明载流子通过浸润层进行传输受到了抑制,由于AlAs引起的相分离机制(113)B量子点的浸润层已经消失或者减小了。(100)面有AlAs盖帽层的PL半高宽的温度依存性与无AlAs盖帽层的量子点大致相同,表明在相同外延条件下相分离机制在(100)面上不如(113)B面显著。     

Photoluminescence and raman scattering characterization of silicon-doped In0.52Al0.48As grown on InP (100) substrates by molecular beam epitaxy

Growth of In_0.52Al_0.48As epilayers on InP (100) substrates by molecular beam epitaxy at different silicon doping levels is carried out. The doped samples show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. There is a reduction in both the AlAs-like and InAs-like longitudinal-optic (LO) phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased. The PL intensity also showed in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.     

多孔硅衬底上ZnS薄膜的白光光致发光

通过脉冲激光沉积（PLD）技术在多孔硅（PS）衬底上制备了ZnS薄膜。用光致发光（PL）的方法观察到白光发射,这个白光是由ZnS薄膜的蓝、绿光和PS的红光叠加形成的。白光光致发光谱是一个从450nm 到700nm的较强的可见光宽谱带。同时研究了激发波长、ZnS薄膜的生长温度、PS的孔隙率和退火温度对ZnS/PS光致发光谱的影响。     

多孔硅衬底上ZnS薄膜的PLD制备和表征

在电化学阳极氧化法制备的多孔硅（porous silicon,PS）衬底上用脉冲激光沉积法（pulsed laser deposition,PLD）在250℃和350℃下生长ZnS薄膜。XRD图样显示,制备的ZnS薄膜沿β—ZnS（111）方向择优生长,较高的生长温度下,衍射峰强度较大。SEM结果表明,250℃生长的Z...     

原位退火对磁控溅射制备的ZnS薄膜微结构和发光性能的影响

采用射频磁控溅射技术在玻璃衬底上制备了系列ZnS薄膜,利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和荧光分光光度计研究了Ar气氛中300～500℃原位退火对薄膜微结构和发光性能的影响.结果表明,退火温度对ZnS薄膜的结晶性能和晶粒大小的影响不大,但会显著影响其发光特性.低温退火处理的薄膜的PL谱具有多个发光峰,...     

ZnS/PS复合体系的制备和性能表征

以电化学阳极氧化法制备的多孔硅（PS）为衬底,用脉冲激光沉积方法分别在200和300℃下制备了ZnS薄膜,得到ZnS/PS复合体系。利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、荧光分光光度计分别对ZnS/PS复合体系的晶体结构、形貌和光致发光（PL）特性进行了研究。XRD结果表明,制备的ZnS薄膜呈立方相晶体结构,沿β-ZnS（111）晶向择优取向生长,生长温度较高的样品的XRD衍射峰强度较大。SEM图像显示,生长温度较高的ZnS薄膜表面较致密平整。室温下的PL谱表明,沉积ZnS薄膜后,PS的发光峰发生蓝移。较高的生长温度下,ZnS的自激活发光强度较大,而PS的红光强度较低且峰位红移。根据三基色叠加的原理,ZnS的蓝绿光与PS的红光叠加在一起,ZnS/PS复合体系呈现出较强的白光发射,为固态白光发射器件的实现开辟了一条新的捷径。     

GaAs-based long-wavelength InAs bilayer quantum dots grown by molecular beam epitaxy

Molecular beam epitaxy growth of a bilayer stacked InAs/GaAs quantum dot structure on a pure GaAs matrix has been systemically investigated.The influence of growth temperature and the InAs deposition of both layers on the optical properties and morphologies of the bilayer quantum dot（BQD） structures is discussed.By optimizing the growth parameters,InAs BQD emission at 1.436μm at room temperature with a narrower FWHM of 27 meV was demonstrated.The density of QDs in the second layer is around 9×10⁹ to 1.4×10¹⁰ cm^-2. The BQD structure provides a useful way to extend the emission wavelength of GaAs-based material for quantum functional devices.