Hiller Kieran P, Winkelmann Aimo, Hourahine Ben, Starosta Bohdan, Alasmari Aeshah, Feng Peng, Wang Tao, Parbrook Peter J, Zubialevich Vitaly Z, Hagedorn Sylvia, Walde Sebastian, Weyers Markus, Coulon Pierre-Marie, Shields Philip A, Bruckbauer Jochen, Trager-Cowan Carol
Advanced Materials Diffraction Lab, Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, UK.
Academic Centre for Materials and Nanotechnology, AGH University of Krakow, Kraków 30-055, Poland.
Microsc Microanal. 2023 Dec 21;29(6):1879-1888. doi: 10.1093/micmic/ozad118.
Extended defects, like threading dislocations, are detrimental to the performance of optoelectronic devices. In the scanning electron microscope, dislocations are traditionally imaged using diodes to monitor changes in backscattered electron intensity as the electron beam is scanned over the sample, with the sample positioned so the electron beam is at, or close to the Bragg angle for a crystal plane/planes. Here, we use a pixelated detector instead of single diodes, specifically an electron backscatter diffraction (EBSD) detector. We present postprocessing techniques to extract images of dislocations and surface steps, for a nitride thin film, from measurements of backscattered electron intensities and intensity distributions in unprocessed EBSD patterns. In virtual diode (VD) imaging, the backscattered electron intensity is monitored for a selected segment of the unprocessed EBSD patterns. In center of mass (COM) imaging, the position of the center of the backscattered electron intensity distribution is monitored. Additionally, both methods can be combined (VDCOM). Using both VD and VDCOM, images of only threading dislocations, or dislocations and surface steps can be produced, with VDCOM images exhibiting better signal-to-noise. The applicability of VDCOM imaging is demonstrated across a range of nitride semiconductor thin films, with varying surface step and dislocation densities.
诸如位错之类的扩展缺陷对光电器件的性能有害。在扫描电子显微镜中，传统上使用二极管对位错进行成像，以监测电子束扫描样品时背散射电子强度的变化，样品的放置方式使得电子束处于或接近某一晶面的布拉格角。在此，我们使用像素化探测器而非单个二极管，具体而言是电子背散射衍射（EBSD）探测器。我们提出了后处理技术，用于从未处理的EBSD图案中的背散射电子强度和强度分布测量中提取氮化物薄膜的位错和表面台阶图像。在虚拟二极管（VD）成像中，监测未处理的EBSD图案中选定部分的背散射电子强度。在质心（COM）成像中，监测背散射电子强度分布中心的位置。此外，这两种方法可以结合使用（VDCOM）。使用VD和VDCOM都可以生成仅包含位错或同时包含位错和表面台阶的图像，其中VDCOM图像具有更好的信噪比。VDCOM成像的适用性在一系列具有不同表面台阶和位错密度的氮化物半导体薄膜中得到了证明。
