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利用金属有机化学气相沉积(MOCVD)技术,在Si(111)衬底上外延生长不同厚度的GaN。外延层薄的GaN表面存在大量的V缺陷,并且V缺陷的两侧有相互平行的带状高坡;外延层厚的GaN表面没有V缺陷,表面平整且晶体质量高。位错处存在晶格畸变,杂质易于在此处聚集,达到一定浓度就会抑制晶体在此处生长而形成V缺陷。受位错附近应力场与气流的影响,V缺陷两侧出现带状高坡。生长时间延长,GaN表面的V缺陷就会被填满,带状高坡横向生长合并成为平整的表面。用m(KOH)∶m(H2O)=1∶10的KOH溶液腐蚀后,平整的表面出现六角腐蚀坑,密度与原生坑密度相近,认为是原生坑被填满的位置腐蚀后再次出现。 相似文献
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为了研究共掺Ce对Nd,Eu∶ZnWO4激光晶体的敏化作用,采用提拉法生长了无宏观缺陷的一系列Nd∶ZnWO4,Ce∶ZnWO4,Eu∶ZnWO4,Ce∶Nd∶ZnWO4和Ce∶Eu∶ZnWO4晶体,并进行了X射线衍射(XRD)、吸收光谱和荧光光谱的测试.测试结果表明,在ZnWO4晶体中Ce3 离子在324 nm附近有很强的吸收,可以有效地吸收抽运能量;Ce3 离子与Nd3 离子和Eu3 离子间存在明显的能量转移,使Nd3 离子在474 nm,572 nm的上转换荧光以及Eu3 离子在613 nm处的荧光强度明显增强,并提出了敏化机制和能量转移过程.结果说明,共掺Ce对Nd,Eu∶ZnWO4激光晶体有较好的敏化作用,有助于提高激光晶体的发光强度. 相似文献
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采用光调制反射光谱(PR)研究了(0001)晶向蓝宝石村底上MOCVD方法生长的单晶六角GaN薄膜的室温光学性质。测得六角GaN薄膜的禁带宽度为3.400eV,对PR谱的调制机理进行了分析,发现信号来自缺陷作用下的表面电场调制。光吸收增和光反射谱的测量,得到3.39eV的光学吸收边和3.3eV的反射峰,证实了光调制反射光谱的结果。 相似文献
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通过改变AlN形核层的生长温度分别在Si(111)衬底上生长了两个GaN样品,并对GaN外延材料表面的六角形缺陷进行了分析研究。通过显微镜和扫描电镜(SEM)观测发现,AlN形核层在高温下生长时,GaN材料表面会产生大量六角形缺陷。通过电子能谱(EDS)分析得出GaN六角形缺陷中含有大量的Si元素以及少量的Ga和Al元素,其中Si元素从Si衬底中高温扩散而来。在降低AlN形核层的生长温度后,GaN材料表面的六角形缺陷随之消失。表明AlN形核层在较低的温度下生长时可以有效地抑制Si衬底表面Si原子的扩散,减少外延层中由于衬底Si反扩散引起的缺陷。 相似文献
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用透射电子显微镜对Si衬底生长GaN/InGaN多量子阱材料进行横断面测试,在衬底和缓冲层区域进行高分辨电子显微成像(HRTEM)、电子衍射衬度成像、选区电子衍射成像,在量子阱附近区域进行了双束近似电子衍衬像对其位错特性进行研究;用场发射扫描电子显微镜对饱和KoH溶液腐蚀前后材料成像.结果发现,AIN缓冲层具有多孔结构,高温GaN层位错平均密度达108cm-2,同扫描电子显微镜得到的六角腐蚀坑密度一致,量子阱以下发现大量位错发生90°弯曲,而使穿过量子阱位错密度大大降低.在线位错中,以刃位错居多,其次是混合位错,所观察区域几乎未见螺位错. 相似文献
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用透射电子显微镜对Si衬底生长GaN/InGaN多量子阱材料进行横断面测试,在衬底和缓冲层区域进行高分辨电子显微成像(HRTEM)、电子衍射衬度成像、选区电子衍射成像,在量子阱附近区域进行了双束近似电子衍衬像对其位错特性进行研究;用场发射扫描电子显微镜对饱和KoH溶液腐蚀前后材料成像.结果发现,AIN缓冲层具有多孔结构,高温GaN层位错平均密度达108cm-2,同扫描电子显微镜得到的六角腐蚀坑密度一致,量子阱以下发现大量位错发生90°弯曲,而使穿过量子阱位错密度大大降低.在线位错中,以刃位错居多,其次是混合位错,所观察区域几乎未见螺位错. 相似文献
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利用深能级瞬态谱( D L T S)和瞬态光电阻率谱( T P R S)研究了利用金属有机物化学气相沉淀( M O C V D)方法生长的未有意掺杂的 In1- x Gax P中缺陷对载流子的俘获和发射过程。利用 D L T S测量观测到了一个激活能为035 e V 的缺陷,由 T P R S测量确定该缺陷的俘获势垒值介于180 m e V 到240m e V 之间。该缺陷的俘获势垒值的大的分布解释为缺陷周围原子重组的微观波动。同时在 T P R S测量中观测到俘获势垒为006 e V 和040 e V 的两个缺陷。 相似文献
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对Si掺杂和Zn掺杂p型GaAs液相外延材料进行光致发光研究。用发射波长为510.6nm和578.2nm的溴化亚铜激光器为激发光源,样品的低温由氦循环致冷机提供,样品室温度在10~300K中可调。在所选取的狭缝宽度下谱仪的分辨率大致为2nm,所提供的数据全部经过系统灵敏度校正并进行分峰拟合。对Si掺杂p型GaAs样品PL谱中一些主要特征进行讨论,认为A_1,A_2,A_3三个发射带分别对应着导带“尾”态中电子向价带和两个浅受主能级的跃迁,它们随温度变化的情况,和带隙宽度及电子填充状态随温度变化有关。此外,我们还观察了掺Zn的p型GaAs样品的PL谱,与掺Si样品比较,具有明显不同的特征,谱线在长波端(~950nm)的上扬趋势表明在低能区域可能存在一个与深能级复合有关的宽发射带。 相似文献
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In Situ Study of Nanostructure and Electrical Resistance of Nanocluster Films Irradiated with Ion Beams
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Weilin Jiang Jennifer A. Sundararajan Tamas Varga Mark E. Bowden You Qiang John S. McCloy Charles. H. Henager Jr. Robert O. Montgomery 《Advanced functional materials》2014,24(39):6210-6218
An in situ study is reported on the structural evolution in nanocluster films under He+ ion irradiation using an advanced helium ion microscope. The films consist of loosely interconnected nanoclusters of magnetite or iron‐magnetite (Fe‐Fe3O4) core‐shells. The nanostructure is observed to undergo dramatic changes under ion‐beam irradiation, featuring grain growth, phase transition, particle aggregation, and formation of nanowire‐like network and nanopores. Studies based on ion irradiation, thermal annealing and electron irradiation have indicated that the major structural evolution is activated by elastic nuclear collisions, while both electronic and thermal processes can play a significant role once the evolution starts. The electrical resistance of the Fe‐Fe3O4 films measured in situ exhibits a super‐exponential decay with dose. The behavior suggests that the nanocluster films possess an intrinsic merit for development of an advanced online monitor for fast neutron radiation with both high detection sensitivity and long‐term applicability, which can enhance safety measures in many nuclear operations. 相似文献
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G.A. Umana-Membreno G. Parish N. Fichtenbaum S. Keller U.K. Mishra B.D. Nener 《Journal of Electronic Materials》2008,37(5):569-572
Electrically active defects in n-GaN films grown with and without an Fe-doped buffer layer have been investigated using conventional and optical deep-level
transient spectroscopy (DLTS). Conventional DLTS revealed three well- defined electron traps with activation energies E
a of 0.21, 0.53, and 0.8 eV. The concentration of the 0.21 and 0.8 eV defects was found to be slightly higher in the sample
without the Fe-doped buffer, whereas the concentration of the 0.53 eV trap was higher in the sample with the Fe-doped buffer.
A minority carrier trap with E
a ≈ 0.65 eV was detected in both samples using optical DLTS; its concentration was ∼40% higher in the sample without the Fe-doped
buffer. Mobility spectrum analysis and multiple magnetic-field measurements revealed that the electron mobility in the topmost
layer of both samples was similar, but that the sample without the Fe-doped buffer layer was affected by parallel conduction
through underlying layers with lower electron mobility. 相似文献
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Stephanie Raabe Daniel Mierwaldt Jim Ciston Matthé Uijttewaal Helge Stein Jörg Hoffmann Yimei Zhu Peter Blöchl Christian Jooss 《Advanced functional materials》2012,22(16):3378-3388
Fundamental studies of catalysts based on manganese oxide compounds are of high interest since they offer the opportunity to study the role of variable valence state in the active state during O2 evolution from H2O. This paper presents a study of doping dependent O2 evolution electrocatalysis of Pr‐doped CaMnO3 via in situ environmental transmission electron microscopy (ETEM) combined with ex situ cyclic voltammetry studies. ETEM studies of heterogeneous catalysis are a challenge, since the reactions in the H2O vapor phase cannot directly be observed. It is shown that the oxidation of silane by free oxygen to solid SiO2‐x can be used to monitor catalytic oxygen evolution. Electron energy loss spectroscopy (EELS) as well as the in situ X‐ray absorption study of near edge structures (XANES) in H2O vapor reveals that the Mn valence is decreased in the active state. Careful TEM analysis of samples measured by ex situ cyclic voltammetry and an in situ bias‐controlled ETEM study allows us to distinguish between self‐formation during oxygen evolution and corrosion at the Pr1‐xCaxMnO3‐H2O interface. Including density functional theory (DFT) calculations, trends in O2 evolution activity and defect chemistry in the active state can be correclated to doping induced changes of the electronic band structure in A‐site doped manganites. 相似文献
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Measurements of the microphotoluminescence (microPL) spectra of InGaN/GaN:Sm and InGaN/GaN:Eu quantum well (QW) structures show that the action of a magnetic field gives rise to Van Vleck paramagnetism for Eu3+ and Sm3+. The macrophotoluminescence (macroPL) spectra recorded after measuring the microPL spectra of InGaN/GaN QW structures doped with Sm or Eu + Sm at a high excitation level (>1023 photons cm?2 s?1) in magnetic fields contain no QW emission lines which are present in the macroPL spectra recorded before these microPL measurements. This is indicative of the presence of photoinduced defects. Annealing of the InGaN/GaN:Sm and InGaN/GaN:(Eu + Sm) structures reduces the concentration of photoinduced defects. 相似文献
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V. Mahalingam M. Tan P. Munusamy J. B. Gilroy M. Raudsepp F. C. J. M. van Veggel 《Advanced functional materials》2007,17(17):3462-3469
In this article we demonstrate the synthesis of Eu2+‐doped GaN/SiO2 nanocomposites using a simple solid state reaction and their use in light‐emitting devices. The nanocomposite exhibits a bright blue luminescence when excited in the UV region (quantum yield = 23 %). The origin of the blue emission is attributed to the presence of europium ions in the +2 oxidation state in the GaN/SiO2 nanocomposites. Analysis of the EPR spectrum of europium‐doped GaN/SiO2 nanocomposites confirms the existence of Eu2+ in the nanocomposites. Various control experiments show that the blue emission arises from these europium ions and that the interface of GaN and silica plays a crucial role. The Eu2+‐doped GaN/SiO2 nanocomposite also exhibits a bright blue electroluminescence. Furthermore, the nanocomposites can be coated with a polymer to tune their dispersibility in organic medium. 相似文献