GaAs纳米线及GaAs/In_xGa_(1-x)As/GaAs纳米线径向异质结构的无催化选区生长的实验研究

利用无催化选区金属有机化学气相沉积(SA-MOCVD)法在GaAs(111)B衬底上分别制备了GaAs纳米线和GaAs/InxGa1-xAs/GaAs纳米线径向异质结构.系统地研究了生长条件对GaAs纳米线生长的影响.实验结果显示,GaAs纳米线的形貌和长度依赖于生长温度、AsH3的分压以及SiO2掩膜表面的圆孔直径.因此可以通过调节以上因素来得到高质量的GaAs纳米线.并且发现扩散是影响无催化选区生长GaAs纳米线的主要机理.微区光致发光谱(μ-PL)表明,GaAs/InxGa1-xAs/GaAs纳米线径向异质结构被成功合成,室温(300 K)下它的发光波长为913 nm.这些结果对于GaAs纳米线及其异质结构制备的进一步研究及其在光电子器件中的应用具有很好的参考价值.     

微槽式光学谐振腔超声传感效应验证*

摘 要：光学微腔的高灵敏度主要源于其结构在时间和空间上对光场的局域增强作用和频率选择作用。其结构在垂直于波导方向上形成了高反射的边界,形成了一种回声腔,使得光在波导内来回反射,从而增强了波导内部的光场强度。当外界存在微小的压力波动时,它将引起波导内部的介电常数和压力场的变化,从而改变了谐振腔内的模式场分布和传输特性,据此可以实现对微小的压力波动进行高灵敏度检测。本文设计了一种高品质因子（Q）的光波导微槽式环形谐振腔超声传感器,完成器件制备并搭建了测试系统,依据倏逝波效应实现了超声探测。测试结果表明,该传感器的品质因子为1.38×107,在800 kHz ~1 MHz范围内响应平坦,在900 kHz的信噪比可以达到27 dB,灵敏度达到 -168 dB。本文设计的传感器可以为水声探测等领域的研究提供关键技术支持。     

Growth and characterization of GaAs/InxGa1-xAs/GaAs axial nanowire heterostructures with symmetrical heterointerfaces

We report on the Au-assisted vapour-liquid-solid （VLS） growth of GaAs/InxGal xAs/GaAs （0.2 ≤ x ≤1） axial double-heterostructure nanowires on GaAs （ 111 ） B substrates via the metal-organic chemical vapor deposition （MOCVD） technique. The influence of the indium （In） content in an Au particle on the morphology of nanowires is investigated systematically. A short period of pre-introduced In precursor before the growth of InxGal xAs segment, coupled with a group III precursor interruption, is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section. The nanowire morphology, such as kinking and tapering, are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.     

利用表面修饰调制GaAs纳米线的电子结构

采用第一性原理的密度泛函方法,研究了利用表面修饰来调制GaAs纳米线的电子结构.在计算中考虑了几种不同的表面钝化材料(H、F、Cl、Br和I)对GaAs纳米线电子结构的影响.计算结果表明,不同的原子修饰GaAs纳米线时对其能带结构的调制主要取决于它们对纳米线表面态的饱和能力.表面修饰不仅可以调节GaAs纳米线的能隙大小,而且也可以调制其能隙类型.GaAs纳米线的电子结构由表面效应和量子限制效应共同来决定.使用不同材料修饰表面的GaAs纳米线的能隙随直径的变化幅度并不相同.表面修饰为实现同种直径和同种结构的GaAs纳米线的能带工程提供了一种新的途径.     

表面悬挂键对GaAs纳米线掺杂的影响及其钝化

利用第一性原理计算方法研究了表面悬挂键对GaAs纳米线掺杂的影响及其钝化．计算结果显示,不论是闪锌矿结构还是纤锌矿结构,GaAs纳米线表面Ga原子上带正电荷的表面悬挂键都是一类稳定的缺陷,并且这种稳定性不会随着纳米线直径的变化而变化．这种表面悬挂键会形成载流子陷阱中心从而从p型掺杂的GaAs纳米线俘获空穴,使得纳米线的掺杂效率下降．和NH₃相比,NO₂ 具有足够的电负性来俘获GaAs纳米线表面悬挂键上的未配对电子,从而有效地钝化GaAs纳米线的表面悬挂键,提高纳米线的p型掺杂效率,并且这种钝化特性不会随着纳米线直径的变化而改变．     

Growth and characterization of GaAs/In_χGa_(1-χ)As/GaAs axialnanowire heterostructures with symmetrical heterointerfaces

We report on the Au-assisted vapour-liquid-solid(VLS) growth of GaAs/InxGa1-xAs/GaAs(0.2 ≤ x ≤ 1) axial double-heterostructure nanowires on GaAs(111) B substrates via the metal-organic chemical vapor deposition(MOCVD) technique.The influence of the indium(In) content in an Au particle on the morphology of nanowires is investigated systematically.A short period of pre-introduced In precursor before the growth of InxGa1-xAs segment,coupled with a group III precursor interruption,is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section.The nanowire morphology,such as kinking and tapering,are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.     

Refocusing and locating effect of fluorescence scattering field

Optical imaging deep inside scattering medium has always been one of the challenges in the field of bioimaging, which significantly drawbacks the employment of con-focal microscopy system. Although a variety of feedback techniques, such as acoustic or nonlinear fluorescence-based schemes have realized the refocusing of the coherent light, the problems of non-invasively refocusing and locating of linearly-excited fluorescent beads inside the scattering medium have not been thoroughly explored. In this paper, we linearly excited the fluorescent beads inside a scattering medium by using our homemade optical con-focal system, collected the fluorescence scattering light as the optimized target, and established a theoretical model of target contrast enhancement, which is consistent with the experimental data. By improving both the cost function and variation rate within the genetic algorithm, we could refocus the fluorescence scattering field while improving the contrast enhancement factor to 12.8 dB. Then, the positions of the fluorescent beads are reconstructed by sub-pixel accuracy centroid localization algorithm, and the corresponding error is no more than 4.2 μ with several fluorescent beads within the field of view. Finally, the main factors such as the number of fluorescent beads, the thickness of the scattering medium, the modulating parameter, the experimental noise and the system long-term stability are analyzed and discussed in detail. This study proves the feasibility of reconstructing fluorescent labeled cells inside biological tissues, which provides certain reference value for deep imaging of biological tissues.     

Fabrication and electrical properties of axial and radial GaAs nanowire pn junction diode arrays

We report on the fabrications and characterizations of axial and radial Ga As nanowire pn junction diode arrays.The nanowires are grown on n-doped Ga As（111）B substrates using the Au-catalyzed vapor–liquid–solid mechanism by metal–organic chemical vapor deposition（MOCVD）. Diethyl–zinc and silane are used as p- and n-type dopant precursors,respectively. Both the axial and radial diodes exhibit diode-like J–V characteristics and have similar performances under forward bias. Under backward bias, the axial diode has a large leakage current, which is attributed to the bending of the pn junction interface induced by two doping mechanisms in Au-catalyzed nanowires. The low leakage current and high rectification ratio make the radial diode more promising in electrical and optoelectronic devices.     

利用表面修饰调制GaAs纳米线的电子结构

采用第一性原理的密度泛函方法,研究了利用表面修饰来调制GaAs纳米线的电子结构. 在计算中考虑了几种不同的表面钝化材料（H、F、Cl、Br 和I）对GaAs纳米线电子结构的影响. 计算结果表明,不同的原子修饰GaAs 纳米线时对其能带结构的调制主要取决于它们对纳米线表面态的饱和能力. 表面修饰不仅可以调节GaAs纳米线的能隙大小,而且也可以调制其能隙类型. GaAs纳米线的电子结构由表面效应和量子限制效应共同来决定. 使用不同材料修饰表面的GaAs纳米线的能隙随直径的变化幅度并不相同. 表面修饰为实现同种直径和同种结构的GaAs纳米线的能带工程提供了一种新的途径.     

表面悬挂键对GaAs纳米线掺杂的影响及其钝化

利用第一性原理计算方法研究了表面悬挂键对GaAs纳米线掺杂的影响及其钝化．计算结果显示,不论是闪锌矿结构还是纤锌矿结构,GaAs纳米线表面Ga原子上带正电荷的表面悬挂键都是一类稳定的缺陷,并且这种稳定性不会随着纳米线直径的变化而变化．这种表面悬挂键会形成载流子陷阱中心从而从p型掺杂的GaAs纳米线俘获空穴,使得纳米线的掺杂效率下降．和NH3相比,NO2 具有足够的电负性来俘获GaAs纳米线表面悬挂键上的未配对电子,从而有效地钝化GaAs纳米线的表面悬挂键,提高纳米线的p型掺杂效率,并且这种钝化特性不会随着纳米线直径的变化而改变．