Novel growth phenomena observed in axial InAs/GaAs nanowire heterostructures
Novel growth phenomena observed in axial InAs/GaAs nanowire heterostructures
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DOI：
10.1002/smll.200700222
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发表时间：
2007-11-01
期刊：
影响因子：
13.3
通讯作者：
Kim, Yong
中科院分区：
文献类型：
--
作者：
Paladugu, Mohanchand;Zou, Jin;Kim, Yong
半导体纳米线以其独特的物理性质在纳米电子器件和纳米光电子器件中具有许多潜在的应用，在过去的十年里引起了广泛的研究关注。半导体纳米线异质结的发展使得单纳米线器件的展示成为可能，如场效应晶体管、发光二极管[3]和纳米线共振隧穿二极管。到目前为止，系统地研究了GaP/GaAs、[5]InP/InAs、[6]及其相关的三元合金[7]的III-V纳米线轴向异质结构，以了解它们的生长行为、异质界面结构和化学以及它们的性质。作为一种重要的光电子应用半导体异质结系统，InxGa1±xAs/GaAs(X1)量子阱异质结[8]在过去得到了广泛的研究。[9]相比之下，在Hiruma等人首次报道后，对一维InAs/GaAs纳米线异质结的研究较少。大约十年前，尽管它们有很好的物理性能和潜在的光电应用，就像它们的2D同行的情况一样。气-液-固(VLS)机制[12]是半导体纳米线及其异质结生长的一种广泛使用的机制。[5]在典型的气-液-固(VLS)生长中，纳米金属合金液滴形成并催化纳米线的生长，因此纳米线及其相关的轴向异质结构的生长前沿有金属颗粒。[5]在纳米线异质结的VLS生长过程中，偶尔会观察到纳米线生长方向的变化，例如，InAs/InP纳米线异质结构。[13]由于这种变化往往伴随着纳米线的物理性质的变化理解这些变化背后的驱动力在科学上很重要，在技术上也是必要的。我们用透射电子显微镜研究了在GaAs纳米线上生长InAs时，InAs生长方向的变化，并从基本生长机制上解释了这一现象。这种生长方向的改变最终导致了InAs在GaAs纳米线上的轴向生长失败。在横流金属-有机化学气相沉积(MOCVD)反应器中，用名义尺寸为%30 nm的Au粒子催化生长InAs/GaAs纳米线异质结构，生长温度为4508℃，温度为100 mbar。纳米线生长的详细过程和生长参数可以在参考文献[14]中找到。首先，用流动的三甲基镓(TMG)和氢化砷(AsH3)分别以1.2×10±5和5.4×10±4molmin1的流量在{111}B(=11 1)的GaAs衬底上生长了30min的GaAs纳米线。为了研究InAs在GaAs纳米线上的初始生长行为，在保持AsH3流速不变的情况下，关闭TMG流并开启三甲基溴化钠(TMI)流，仅在1min内生长了InAs纳米线。用扫描电子显微镜(SEM，JEOL 890)和透射电子显微镜(Tecnai F30和Tecnai F20配备扫描电子显微镜(STEM)和能谱(EDS)设备)对所制备的纳米线异质结构进行了表征。将纳米线在乙醇中超声10min，然后分散在多孔碳膜上，制备了透射电子显微镜样品。图1a是一张扫描电子显微镜图像，显示了…中InAs/GaAs线异质结的典型形貌
Semiconductor nanowires have many potential applications in nanoelectronic and nano-optoelectronic devices owing to their unique physical properties,[1] which have drawn extensive research attention in the past decade. The growth of semiconductor nanowire heterostructures has enabled the demonstration of single-nanowire devices, such as fieldeffect transistors,[2] light-emitting diodes [3] and nanowire resonant tunneling diodes.[4] Nanowire heterostructures of III–V materials are of particular interest for their optoelectronic applications. So far, III–V nanowire axial heterostructures of GaP/GaAs,[5] InP/InAs,[6] and their related ternary alloys [7] have been studied systematically to understand their growth behavior, hetero-interfacial structure and chemistry, and their properties. As a key semiconductor heterostructure system for optoelectronic applications,[8] twodimensional (2D) InxGa1ÀxAs/GaAs (x 1) quantum-well heterostructures have been studied extensively in the past.[9] In comparison, 1D InAs/GaAs nanowire heterostructures have been less studied [10] after the first report by Hiruma et al. about a decade ago,[11] in spite of their promising physical properties and potential optoelectronic applications, as in the case of their 2D counterparts. The vapor–liquid–solid (VLS) mechanism [12] has been a widely used mechanism for the growth of semiconductor nanowires and their heterostructures.[5] In typical VLS growth, nanosized metal-alloy liquid droplets form and then catalyze nanowire growth, so that the nanowires and their associated axial heterostructures have metal particles at their growth front.[5] During VLS growth of nanowire heteroACHTUNGTRENNUNGstructures, changes in nanowire growth directions have been occasionally observed, for example, in the case of InAs/InP nanowire heterostructures.[13] Since such a change is often accompanied by changes in the physical properties of the nanowire, it is scientifically important and technologically necessary to understand the driving force behind these changes. We use transmission electron microscopy (TEM) to study the changes in the InAs growth direction when it is grown on GaAs nanowires, and we account for this phenomenon in terms of the fundamental growth mechanism. This change in the growth direction ultimately leads to the failure of InAs axial growth on the GaAs nanowires. The growth of InAs/GaAs nanowire heterostructures was catalyzed by Au particles with a nominal size of% 30 nm in a horizontal-flow metal-organic chemical vapor deposition (MOCVD) reactor at 100mbar with a growth temperature of 4508C. The detailed process and growth parameters for the nanowire growth can be found in Ref.[14]. Initially, GaAs nanowires were grown on a {111} B (=(1 1 1)) GaAs substrate for 30min by flowing trimethylgallium (TMG) and AsH3 at flow rates of 1.2 10À5 and 5.4 10À4 mol minÀ1, respectively. To study the initial growth behavior of InAs on GaAs nanowires, InAs nanowire sections were grown for only 1min on the GaAs nanowires by switching off the TMG flow and switching on a trimethylindium (TMI) flow at 1.2 10À5 mol minÀ1 while maintaining the AsH3 flow rate.The fabricated nanowire heterostructures were characterized by scanning electron microscopy (SEM, JEOL 890) and TEM (Tecnai F30 and Tecnai F20 equipped with scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) facilities). TEM specimens were prepared by ultrasonicating the nanowires in ethanol for 10 min followed by dispersal onto holey carbon films. Figure1a is an SEM image showing the typical morphology of the InAs/GaAs nanowire heterostructures …