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Optical and electrical properties of compound and transition metal doped compound semiconductor nanowires.

机译：化合物和过渡金属掺杂的化合物半导体纳米线的光学和电学性质。

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摘要

Nanotechnology is the science and engineering of creating functional materials by precise control of matter at nanometer (nm) length scale and exploring novel properties at that scale. It is vital to understand the quantum mechanical phenomena manifested at nanometer scale dimensions since that will enable us to precisely engineer quantum mechanical properties to realize novel device functionalities. This dissertation investigates optical and electronic properties of compound and transition metal doped compound semiconductor nanowires with a view to exploiting them for a wide range of applications in semiconductor electronic and optical devices.;In this dissertation work, basic concepts of optical and electronic properties at low dimensional structures will be discussed in chapter 1. Chapter 2 discusses the nanofabrication technique employed to fabricate highly ordered nanowires. Using this method, which is based on electrochemical self-assembly techniques, we can fabricate highly ordered and size controlled nanowires and quantum dots of different materials. In Chapter 3, we report size dependent fluorescence spectroscopy of ZnSe and Mn doped ZnSe nanowires fabricated by the above method. The nanowires exhibit blue shift in the emission spectrum due to quantum confinement effect, which increases the effective bandgap of the semiconductor. We found that the fluorescence spectrum of Mn doped ZnSe nanowires shows high luminescence efficiency, which seems to increase with increasing Mn concentration. These results are highly encouraging for applications in multi spectral displays. Chapter 4 investigates field emission results of highly ordered 50 nm tapered ZnO nanowires that were also fabricated by electrochemical self-assembly. Subsequent to fabrication, the nanowires tips are exposed by chemical etching which renders the tips conical in shape. This tapered shape concentrates the electric field lines at the tip of the wires, and that, in turn, increases the emission current density while lowering the threshold field for the onset of field emission. Measurement of the Fowler-Nordheim tunneling current carried out in partial vacuum indicates that the threshold electric field for field emission in 50-nm diameter ZnO nanowires is 15 V/microm. In this study we identified the key constraint that can increase the threshold field and reduce emission current density. In Chapter 5 we report optical and magnetic measurement of Mn-doped ZnO nanowires. Hysterisis measurements carried out at various temperatures show a ferromagnetic behavior with a Curie temperature of ∼ 200 K. We also studied Mn-doping of the ZnO nanowires. The room temperature fluorescence spectroscopy of Mn-doped ZnO nanowires shows a red-shift in the spectra compared to the undoped ZnO nanowires possibly due to strain introduced by the dopants in the nanowires. Finally, in Chapter 6, we report our study of the ensemble averaged transverse spin relaxation time (T2*) in InSb thin films and nanowires using electron spin resonance (ESR) measurement. Unfortunately, the nanowires contained too few spins to produce a detectable signal in our apparatus, but the thin films contained enough spins (> 10 9/cm2) to produce a measurable ESR signal. We found that the T2* decreases rapidly with increasing temperature between 3.5 K and 20 K, which indicates that spin-dephasing is primarily caused by spin-phonon interactions.
机译：纳米技术是通过精确控制纳米级尺度的物质并探索该尺度下的新特性来创建功能性材料的科学和工程技术。了解纳米尺度上表现出的量子力学现象至关重要，因为这将使我们能够精确地设计量子力学特性，以实现新颖的器件功能。本文研究了化合物和过渡金属掺杂的化合物半导体纳米线的光学和电子性能，以期将其用于半导体电子和光学器件中的广泛应用。第1章将讨论尺寸结构。第2章讨论了用于制造高度有序的纳米线的纳米制造技术。使用这种基于电化学自组装技术的方法，我们可以制造高度有序且受尺寸控制的纳米线和不同材料的量子点。在第三章中，我们报告了通过上述方法制造的ZnSe和Mn掺杂的ZnSe纳米线的尺寸依赖性荧光光谱。由于量子限制效应，纳米线在发射光谱中表现出蓝移，这增加了半导体的有效带隙。我们发现锰掺杂的ZnSe纳米线的荧光光谱显示出高的发光效率，似乎随着锰浓度的增加而增加。这些结果对于多光谱显示器中的应用非常令人鼓舞。第4章研究了也通过电化学自组装制造的高度有序的50 nm锥形ZnO纳米线的场发射结果。在制造之后，纳米线尖端通过化学蚀刻被暴露，这使得尖端呈圆锥形。这种锥形形状将电场线集中在导线的末端，进而增加了发射电流密度，同时降低了场发射开始时的阈值场。在部分真空中进行的Fowler-Nordheim隧穿电流的测量表明，直径为50 nm的ZnO纳米线中用于场发射的阈值电场为15 V /μm。在这项研究中，我们确定了可以增加阈值场并降低发射电流密度的关键约束。在第5章中，我们报告了Mn掺杂的ZnO纳米线的光学和磁性测量。在不同温度下进行的磁滞测量显示出居里温度约为200 K的铁磁行为。我们还研究了ZnO纳米线的Mn掺杂。 Mn掺杂的ZnO纳米线的室温荧光光谱显示，与未掺杂的ZnO纳米线相比，光谱中的红移可能是由于掺杂剂在纳米线中引入的应变所致。最后，在第6章中，我们使用电子自旋共振（ESR）测量报告了InSb薄膜和纳米线中整体平均横向自旋弛豫时间（T2 *）的研究。不幸的是，纳米线的自旋太少，无法在我们的设备中产生可检测的信号，但是薄膜却包含足够的自旋（> 10 9 / cm2），无法产生可测量的ESR信号。我们发现，随着温度在3.5 K和20 K之间升高，T2 *迅速降低，这表明自旋相移主要是由自旋声子相互作用引起的。

著录项

  • 作者

    Ramanathan, Sivakumar.;

  • 作者单位

    Virginia Commonwealth University.;

  • 授予单位 Virginia Commonwealth University.;
  • 学科 Engineering Electronics and Electrical.;Engineering Materials Science.;Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 115 p.
  • 总页数 115
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 无线电电子学、电信技术;工程材料学;
  • 关键词

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