原位等离子体逐层氧化a-Si:H/SiO2多层膜的光致发光研究

采用在等离子体增强化学汽相沉积系统中沉积a-Si:H和原位等离子体逐层氧化的方法制备a-Si:H/SiO2多层膜.改变a-Si:H层的厚度，首次在室温下观察到来自a-Si:H/SiO2多层膜较强的蓝色光致发光和从465到435nm的蓝移.x射线能谱证明，SiO2层是化学配比的SiO2；C-V特性表明，a-Si:H/SiO2界面得到了很好的钝化；透射电子显微镜表明，样品形成了界面陡峭的多层结构.结合光吸收谱和光致发光谱的研究，对其发光机理进行了讨论.用一维量子限制模型对光致发光峰随着a-Si:H层厚度的减小 关键词： a-Si:H/SiO2多层膜 光致发光     

不同盖层对InAs/GaAs量子点结构和光学性质的影响

利用金属有机化合物气相沉积设备生长了不同盖层结构的InAs/GaAs量子点,采用原子力显微镜和光致发光光谱仪对量子点的结构和光学性质进行了研究.量子点层之间的盖层由一个低温层和一个高温层组成.对不同材料结构的低温盖层的对比研究表明,In组分渐变的InGaAs低温盖层有利于改善量子点均匀性、减少结合岛数目、提高光致发光强度;当组分渐变InGaAs低温盖层厚度由6.8 nm增加到12 nm,发光波长从1256.0 nm红移到1314.4 nm.另外,还对不同材料结构的高温盖层进行了对比分析,发现高温盖层采用In组分渐变的InGaAs材料有利于光致发光谱强度的提高. 关键词： 半导体量子点 盖层 组分渐变     

Inter-Layer Energy Transfer through Wetting-Layer States in Bi-layer InGaAs/GaAs Quantum-Dot Structures with Thick Barriers

The inter-layer energy transfer in a bi-layer InGaAs/GaAs quantum dot structure with a thick GaAs barrier is studied using temperature-dependent photoluminescence. The abnormal enhancement of the photoluminescence of the QDs in the layer with a larger amount of coverage considering the resonant Forster energy transfer between the at 110K is observed, which can be explained by wetting layer states at elevated temperatures.     

失配应力引起的Ga_xIn_（1－x）P外延层能带隙的移动

本文首次观察了用ＭＯＣＶＤ方法生长的ＧａｘＩｎ１－ｘＰ外延层的能带隙移动，并给出了ＧａｘＩｎ１－ｘＰ外延层光荧光（ＰＬ）峰能量随组分ｘ的变化关系，结果表明ＰＬ是探测混晶组分的简单而有效的方法之一。     

有机阱结构器件在反向偏压调制下光致发光猝灭的研究

实验过程中制备了3种不同周期的有机阱结构器件,分别用N,N’-diphenyl-N,N’-bis(1-napthyl)-1,1’-biphenyll-4,4’-diamine(NPB)和4,4,N,N’-dicarbazolebiphenyl(CBP)作为电子的势阱和势垒。讨论了3个器件在反向偏压调制下的光致发光的猝灭。研究结果显示在作者所制备的器件中NPB层中激子的猝灭速度要比CBP层中的激子猝灭速度快。这主要是因为NPB层中的有效电场要比CBP层中的有效电场强。当所制备的有机阱结构器件的周期数增加时,在相同的反向电场下,NPB和CBP层中的激子猝灭速度会随之增加,因为实验中制备的这3个器件为Ⅱ型量子阱结构,激子在这种阱结构器件中会随着阱周期数的增加而变得越来越不稳定,因此周期数较大的器件猝灭现象比较明显。     

硅基低位错密度厚锗外延层的UHV/CVD法生长

利用超高真空化学气相淀积系统, 基于低温缓冲层和插入应变超晶格的方法, 在Si(100)衬底上外延出厚度约为880 nm的纯Ge层. 采用X射线双晶衍射、高分辨透射电镜、原子力显微镜和光致发光谱分别表征了其结构及光学性质. 测试结果显示外延Ge的X射线双晶衍射曲线半高宽为273", 表面均方根粗糙度为0.24 nm, 位错密度约为1.5×10⁶ cm². 在室温下观测到外延Ge的直接带跃迁光致发光, 发光峰值位于1540 nm. 表明生长的Si基Ge材料具有良好的结晶质量, 可望在Si基光电子器件中得到应用.     

Quantum dot light emitting diodes using size-controlled ZnO NPs

The particle size and trap energy level of ZnO were adjusted by varying the concentration of precursors using a sol–gel process, and the energy transport properties of the electron transport layer in quantum dot light-emitting diodes (QD-LEDs) were analyzed. Thus far, no study has considered the efficient electron transport properties of quantum dot light-emitting devices with respect to trap energy levels owing to the oxygen vacancies of ZnO. The particle size and trap energy levels of ZnO were analyzed based on optical properties such as photoluminescence and absorbance. The optimized device showed excellent performance, with a maximum luminance of 50,120 cd/m², a high efficiency of 5.85 cd/A, and a threshold voltage of 2.5 V. The Y-ZnO (yellow photoluminescence ZnO)-based QD-LEDs not only enhanced the injection efficiency of electrons into the emitting layer but also confined the holes in the emitting layer due to the shallow trap level of Y-ZnO, in contrast to the deep trap levels of G-ZnO (green photoluminescence ZnO) and B-ZnO (blue photoluminescence ZnO). Here, we present the first attempt to analyze the electron transport behavior of the electron transport layer of the resulting device.     

Electrochemical deposition of cerium on porous silicon to improve photoluminescence properties

In this work, we present results for Cerium (Ce) doping effects on photoluminescence (PL) properties of porous silicon (PS). Cerium was deposited using electrochemical deposition on porous silicon prepared by electrochemical anodization of P-type (100) Si. From the photoluminescence spectroscopy, it was shown that porous silicon treated with cerium can lead to an increase of photoluminescence when they are irradiated by light compared to the porous silicon layer without cerium. In order to understand the contribution of cerium to the enhanced photoluminescence, energy dispersive X-ray (EDX) spectroscopy, Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and atomic force microscopy (AFM) were performed, and it was shown that the improved photoluminescence may be attributed to the change of Si–H bonds into Si–O–Ce bonds and to a newly formed PS layer during electrochemical Ce coating.     

Influence of GaAsSb structural properties on the optical properties of InAs/GaAsSb quantum dots

The optical properties of InAs quantum dots with GaAsSb buffer, capping and cladding layers of different alloy compositions are studied by photoluminescence techniques. Fully strained GaAsSb layers show that the inclusion of a buffer layer gives a blue-shift to quantum dot emission, while for quantum dots capped with GaAsSb a clear red-shift is seen. Power-dependent photoluminescence suggests a transition from type-I to type-II can be achieved by GaAsSb at Sb composition between 11–13%, while the transition for the GaAsSb cladding layer occurs at around 11%. At low Sb composition, good crystal quality and energy barrier are detected by temperature-dependent photoluminescence, while high-level dislocation and defects exist under high antimony content, as evidenced by X-Ray Diffraction and Transmission Electron Microscopy.     

Recombination processes in structures with GaN/ALN quantum dots

Mechanisms of the generation and the radiative and nonradiative recombination of carriers in structures with GaN quantum dots in the AlN matrix are studied experimentally and theoretically. Absorption, stationary and nonstationary photoluminescence of quantum dots at different temperatures are investigated. It is found that the photoluminescence intensity considerably decreases with the temperature while the photoluminescence kinetics weakly depends on the temperature. The photoluminescence kinetics is shown to be determined by radiative recombination inside quantum dots. A mechanism of nonradiative recombination is proposed, according to which the main reason for the thermal quenching of photoluminescence is nonradiative recombination of charge carriers, generated by optical transitions between quantum dots and wetting layer states.     

Investigation of populated InAs/GaAs quantum dots by photoluminescence and photoreflectance

We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10 K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state.     

Relationship between the electric performance and the photoluminescence spectra of resonant tunnelling diodes

Resonant tunnelling diodes with different structures were grown. Their photoluminescence spectra were investigated. By contrast, the luminescence in the quantum well is separated from that of other epilayers. The result is obtained that the exciton of the luminescence in the quantum well is partly come from the cap layer in the experiment. So the photoluminescence spectrum is closely related to the electron transport in the resonant tunnelling diode structure. This offers a method by which the important performance of resonant tunnelling diode could be forecast by analysing the integrated photoluminescence intensities.     

Band bending of n‐InN epilayers and exact solution of the classical Thomas–Fermi equation

The exact solution of the Thomas–Fermi equation for a planar accumulation layer of a degenerate semiconductor is presented. The obtained results are compared with theoretical literature data. The applicability of the solution is demonstrated by using results of electrochemical capacitance–voltage measurements and photoluminescence data for n‐InN epilayers. It has been found that the difference between the electron concentrations estimated from the Hall and photoluminescence measurements is a measure of the electron content in the accumulation layer with acceptable accuracy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Identification of excitons,trions and biexcitons in single‐layer WS2

Single‐layer WS₂ is a direct‐gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature‐dependent photoluminescence measurements on mechanically exfoliated single‐layer WS₂, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n‐type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Controllable hydrothermal synthesis of ZnO nanowires arrays on Al-doped ZnO seed layer and patterning of ZnO nanowires arrays via surface modification of substrate

ZnO nanowire (NW) arrays are assembled on the Al-doped ZnO (AZO) seed layer by a hydrothermal process. Effects of the temperature and growth time of the hydrothermal process on morphological and photoluminescence properties of the as-assembled ZnO NW arrays are characterized and studied. Results indicate that the length and diameter of the ZnO NWs increase with a lengthening of the growth time at 80 °C and the hydrothermal temperature has a significant effect on the growth rate and the photoluminescence properties of the ZnO NW arrays. The patterned AZO seed layer is fabricated on a silicon substrate by combining a sol-gel process with an electron-beam lithography process, as well as a surface fluorination technique, and then the ZnO NW arrays are selectively grown on those patterned regions of the AZO seed layer by the hydrothermal process. Room-temperature photoluminescence spectra of the patterned ZnO NW arrays shows that only a strong UV emission at about 380 nm is observed, which implies that few crystal defects exist inside the as-grown ZnO NW arrays.     

Optical and structural investigation of a-plane GaN layers on r-plane sapphire with nucleation layer optimization

Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers:(A) a GaN nucleation layer deposited at low temperature(LT);(B) an AlN nucleation layer deposited at high temperature;or(C) an LT thin AlN nucleation layer with an AlN layer and an AlN/AlGaN superlattice both subsequently deposited at high temperature.The samples have been characterized by Xray diffraction(XRD),atomic force microscopy and photoluminescence.The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A,indicating a reduction in crystal defect density.Furthermore,the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely.The improved optical property,corresponding to the enhanced crystal quality,is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements.     

a-Si:H/a-SiNx:H超晶格薄膜光致发光性质的研究

本文报道了a-Si:H/a-SiNx:H超晶格薄膜光致发光某些性质的研究。实验发现,这种超晶格薄膜光致发光的强度和峰值能量随交替层a-Si:H厚度,测量温度及光照时间等而变化。同时还发现,在阴、阳两极上,利用GD法沉积的样品,发光强度和峰值能量也有所不同。文中对这些实验结果作了初步解释。     

PHOTOLUMINESCENCE AND RAMAN SCATTERING OF PURE GERMANIUM/SILICON SHORT PERIOD SUPERLATTICE

Pure Ge/Si short period superlattice (SPS) samples grown by gas source molecular beam epitaxy (GS-MBE) were studied by photoluminescence and Raman scattering. For SPS samples with Germanium layer thickness (L_Ge) of 1.5 monolayer (ML), a new band of photoluminescence is observed for silicon layer thickness (L_Si) in an intermediate range of 1.9-2.9 nm. In contrast to pure Ge/Si quantum wells, the energy of the new band shows a red-shift with the increase of L_Si. Raman scattering results show that when the intensity of the photoluminescence of the new band reaches a maximum, the Raman shift relating the vibration of Si-Si reaches a minimum. It is therefore considered that the new band of the pure Ge/Si SPS is related with some kind of strain relaxation process.     

分子束外延生长ZnSe自组织量子点光、电行为研究

分别应用光致发光、电容电压和深能级瞬态傅里叶谱技术详细研究ZnSe自组织量子点样品的光学和电学行为.光致发光温度关系表明ZnSe量子点的光致发光热猝火过程机理.两步猝火过程的理论较好模拟和解释了相关的实验数据.电容电压测量表明样品表观载流子积累峰出现的深度(样品表面下约100nm处)大约是ZnSe量子点层的位置.深能级瞬态傅里叶谱获得的ZnSe量子点电子基态能级位置为ZnSe导带下的011eV,这与ZnSe量子点光致发光热猝火模型得到的结果一致.     

用小功率He-Ne激光器测量Ga1-xAlxAs外延片表面组份的均匀性

本文描述了一种简便可靠的分析Ga1-xAlxAs外延片表面组份均匀性的光学方法.在300K下,用小功率He-Ne激光器作光源,对x<0.39的n型和p型外延层进行了光致发光测量.依据光谱峰值获得表面的x值与扫描电镜所得结果相符.通过激发表面不同点处测得的光致发光光谱的位移,可以迅速而直观地分析出x值分布的均匀性.