Ballistic Electron Emission Luminescence and Microscopy for Complementary Optical and Electronic Characterization of Buried III-V Semiconductor Heterostructures on the Local Scale

为了提高量子器件的性能，对半导体结构的纳米级表征的需求越来越大。在先前的NSF支持下，PI率先使用弹道电子发射显微镜（BEEM）作为一种强大的新型低能电子显微镜，用于横向成像和光谱（也具有纳米分辨率），用于放置在地表以下10纳米的埋藏结构。他们现在提出了一种新的BEEM变体，通过增加同步BEEM诱导发光（BEEL）的能力来探测基于砷化物，氮化物，磷化物和锑化物的新型光电量子异质结构。BEEM和光子的结合提供了明显的优势。首先，通过探测从BEEM发射的光子，灵敏的光学技术可以用于探测和分析。因此，光子代表了研究半导体异质结构的特别丰富的附加信息通道。其次，通过用BEEM激发光子发射，使用了一个定义明确的光源。它的横向延伸是原子尺寸（~几纳米），它与样品的距离是任何近场技术的关键因素，可以用皮米级精度控制。第三，对BEEM和BEEL进行比较分析，可以同时对埋藏半导体结构的光学和电子特性进行高空间分辨率的空间映射，并研究它们之间的相关性。利用集成的BEEM/BEEL系统，我们将使用BEEM尖端的隧道电子束作为BEEL的局部激发源，研究埋藏半导体结构的光学和输运特性。这样，除了BEEM电流外，他们还将记录BEEL光谱以及BEEL图作为尖端横向位置的函数。为了有效地收集发光信号，同时保持尖端到样品区良好的热隔离和电隔离，他们建议使用靠近样品的高数值孔径光纤。此外，使用金属涂层光纤作为STM尖端将使我们能够利用NSOM和BEEM组合测量的优势。该结构的可选光激发也将使他们能够研究空间分辨光致发光（PL）和PL激发以及BEEM电流的光电调制。使用BEEM/ beel进行的此类研究以前从未做过。通过这样的研究，他们希望推进他们对技术上重要的量子结构（如AlGaN/GaN和GaInP/GaAs量子阱以及InP和GaSb自组装量子点）中的载流子输运和重组动力学的理解，对自发有序的GaInP2、合金中有序的影响，以及GaN中纳米级缺陷和位错的理解

9906047NarayanamurtiTo improve the performance of quantum devices, there is an increasing demand for nanometer-scale characterization of semiconductor structures. Under prior NSF support, The PI's have pioneered the use of the Ballistic electron emission microscopy (BEEM) as a powerful new low energy electron microscopy for lateral imaging and spectroscopy (also with nm resolution) for buried structures placed up to 10 nm below the surface.They now propose a novel variant of BEEM by adding the capability of simultaneous BEEM-induced luminescence (BEEL) to probe novel optoelectronic quantum heterostructures based on arsenides, nitrides, phosphides, and antimonides.A combination of BEEM and photons offers distinct advantages. First, by detecting photons emitted from a BEEM, sensitive optical techniques may be used for detection and analysis. Photons thus represent a particularly rich, additional channel of information to study semiconductor heterostructures. Second, by exciting the photon emission with BEEM, a well-defined source is used. Its lateral extension is of atomic dimensions (~ few nm) and its distance from the sample, a crucial factor in any near-field technique, may be controlled with picometer precision. Third, a comparative analysis of BEEM and BEEL would allow simultaneous spatial mapping of both optical and electronic properties of buried semiconductor structures with high spatial resolution and to study their correlation.The optical and transport properties of the buried semiconductor structures will be studied by using the integrated BEEM/BEEL system, wherein we will use a tunneling-electron beam from the tip of BEEM as a local excitation source of BEEL. In this way, in addition to BEEM current, they will record BEEL spectra as well as maps of BEEL as a function of lateral position of the tip. To collect effectively the luminescence signal while conserving a good thermal and electrical isolation of the tip-to-sample zone, they propose to use high numerical-aperture fibers spaced close to the sample. In addition, the use of a metal-coated optical fiber as a STM tip will allow us to take an advantage of the combined NSOM and BEEM measurements. Optional photoexcitation of the structure will also allow them to study spatially-resolved photoluminescence (PL) and PL excitation as well as the BEEM current photomodulation.Such studies using BEEM/BBEEL have never been done before. Through such studies, they expect to advance their understanding of carrier transport and recombination dynamics in technologically important quantum structures such as AlGaN/GaN and GaInP/GaAs quantum wells as well as InP and GaSb self-assembled quantum dots, of the effect of ordering in spontaneously ordered GaInP2, alloys, and of the nano-scaled defects and dislocations in GaN.***