Kazanowska Barbara A, Sapkota Keshab R, Lu Ping, Talin A Alec, Bussmann Ezra, Ohta Taisuke, Gunning Brendan P, Jones Kevin S, Wang George T
University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611, United States of America.
Sandia National Laboratories, Albuquerque, NM 87185, United States of America.
Nanotechnology. 2021 Oct 27;33(3). doi: 10.1088/1361-6528/ac2981.
The controlled fabrication of vertical, tapered, and high-aspect ratio GaN nanowires via a two-step top-down process consisting of an inductively coupled plasma reactive ion etch followed by a hot, 85% HPOcrystallographic wet etch is explored. The vertical nanowires are oriented in the[0001]direction and are bound by sidewalls comprising of{336¯2}semipolar planes which are at a 12° angle from the [0001] axis. High temperature HPOetching between 60 °C and 95 °C result in smooth semipolar faceting with no visible micro-faceting, whereas a 50 °C etch reveals a micro-faceted etch evolution. High-angle annular dark-field scanning transmission electron microscopy imaging confirms nanowire tip dimensions down to 8-12 nanometers. The activation energy associated with the etch process is 0.90 ± 0.09 eV, which is consistent with a reaction-rate limited dissolution process. The exposure of the{336¯2}type planes is consistent with etching barrier index calculations. The field emission properties of the nanowires were investigated via a nanoprobe in a scanning electron microscope as well as by a vacuum field emission electron microscope. The measurements show a gap size dependent turn-on voltage, with a maximum current of 33 nA and turn-on field of 1.92 V nmfor a 50 nm gap, and uniform emission across the array.
探索了通过两步自上而下的工艺可控地制造垂直、锥形和高纵横比的氮化镓纳米线，该工艺包括电感耦合等离子体反应离子蚀刻，随后是85%热磷酸的晶体学湿法蚀刻。垂直纳米线沿[0001]方向取向，并由包含{336¯2}半极性平面的侧壁界定，这些侧壁与[0001]轴成12°角。在60°C至95°C之间进行高温磷酸蚀刻会产生光滑的半极性刻面，没有可见的微刻面，而50°C蚀刻则显示出微刻面蚀刻演变。高角度环形暗场扫描透射电子显微镜成像证实纳米线尖端尺寸低至8-12纳米。与蚀刻过程相关的活化能为0.90±0.09 eV，这与反应速率限制的溶解过程一致。{336¯2}型平面的暴露与蚀刻势垒指数计算一致。通过扫描电子显微镜中的纳米探针以及真空场发射电子显微镜研究了纳米线的场发射特性。测量结果显示开启电压与间隙尺寸有关，对于50纳米间隙，最大电流为33 nA，开启场为1.92 V/nm，并且阵列中发射均匀。
