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Strained-Germanium Nanomembranes for Potential Direct-Gap Luminescence

机译：应变锗纳米膜用于潜在的直接间隙发光

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摘要

Inorganic-semiconductor nanomembranes (NMs), i.e., single-crystal sheets with sub-micron thicknesses, have recently emerged as a promising materials platform for a wide range of fundamental studies and device applications. In the context of group-IV semiconductor optoelectronics, a particularly compelling function is the formation of direct-bandgap germanium in mechanically stressed NMs for optical applications. Similar to most other group-IV semiconductors, unstrained Ge has an indirect fundamental energy bandgap, which results in exceedingly low radiative efficiency. Extensive calculations, however, have shown that tensile strain can be used to lower the direct conduction band edge relative to the indirect one, to the point that large optical gain can be established under practical pumping conditions. The fundamental bandgap even becomes direct if the strain exceeds a certain threshold that is generally found to be 1.7%-2% biaxial. In this dissertation, the introduction of 1.8% biaxial strain has been confirmed in sufficiently thin Ge NMs, as well as the emission enhancement and red shift observed in the photolumines-cence measurements. An optical cavity is fabricated and integrated with the Ge NM, in order to enhance the emission intensity in the mid-infrared range. A lateral P-I-N diode is fabricated based on the Ge NMs, to attempt to observe for the first-time electroluminescence as a function of strain in Ge. Finally, I investigate ways to increase the maximum strain that a Ge NM of a given thickness can tolerate. These ways include improving the structural quality of Ge NMs, improving NM releasing methods, and using graphene to protect the Ge NM surfaces from ambient attack. Some improvement in strain tolerance is noted.
机译：无机半导体纳米膜（NMs），即具有亚微米厚度的单晶片，最近已成为用于广泛基础研究和器件应用的有前途的材料平台。在第IV组半导体光电子学的背景下，一个特别引人注目的功能是在机械应力的NM中为光学应用形成直接带隙锗。与大多数其他IV类半导体类似，未应变的Ge具有间接的基本能带隙，导致辐射效率极低。但是，大量的计算表明，可以使用拉伸应变来降低直接导带边缘相对于间接导带边缘的程度，以至在实际泵浦条件下可以建立较大的光学增益。如果应变超过某个阈值（通常发现是双轴的1.7％-2％），则基本带隙甚至变得直接。在本文中，已证实在足够薄的Ge NM中引入了1.8％的双轴应变，以及在光致发光测量中观察到的发射增强和红移。制作了一个光腔并将其与Ge NM集成在一起，以增强中红外范围内的发射强度。基于Ge NM制造横向P-I-N二极管，以尝试观察首次电致发光与Ge中应变的关系。最后，我研究了增加给定厚度的Ge NM可以承受的最大应变的方法。这些方法包括改善Ge NM的结构质量，改进NM释放方法以及使用石墨烯保护Ge NM表面免受环境侵蚀。注意到应变耐受性有所改善。

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  • 作者

    Cui, Xiaorui.;

  • 作者单位

    The University of Wisconsin - Madison.;

  • 授予单位 The University of Wisconsin - Madison.;
  • 学科 Materials science.;Electrical engineering.
  • 学位 Ph.D.
  • 年度 2018
  • 页码 108 p.
  • 总页数 108
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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