Brubaker Matt D, Roshko Alexana, Berweger Samuel, Blanchard Paul T, Little Charles A E, Harvey Todd E, Sanford Norman A, Bertness Kris A
Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, CO, United States of America.
Nanotechnology. 2020 Jun 24;31(42):424002. doi: 10.1088/1361-6528/ab9fb2.
Lateral piezoresponse force microscopy (L-PFM) is demonstrated as a reliable method for determining the crystallographic polarity of individual, dispersed GaN nanowires that were functional components in electrical test structures. In contrast to PFM measurements of vertically oriented (as-grown) nanowires, where a biased probe tip couples to out-of-plane deformations through the d piezoelectic coefficient, the L-PFM measurements in this study were implemented on horizontally oriented nanowires that coupled to shear deformations through the d coefficient. L-PFM phase-polarity relationships were determined experimentally using a bulk m-plane GaN sample with a known [0001] direction and further indicated that the sign of the d piezoelectric coefficient was negative. L-PFM phase images successfully revealed the in-plane [0001] orientation of self-assembed GaN nanowires as part of a growth polarity study and results were validated against scanning transmission electron microscopy lattice images. Combined characterization of electrical properties and crystallographic polarity was also implemented for two-terminal GaN/AlGaN/GaN nanowires devices, demonstrating L-PFM measurements as a viable tool for assessing correlations between device rectification and polarization-induced band bending.
横向压电力显微镜（L-PFM）被证明是一种可靠的方法，用于确定作为电测试结构功能组件的单个分散GaN纳米线的晶体极性。与垂直取向（生长态）纳米线的压电力显微镜测量不同，在垂直取向纳米线的测量中，有偏置的探针尖端通过d压电系数与面外变形耦合，而本研究中的L-PFM测量是在通过d系数与剪切变形耦合的水平取向纳米线上进行的。使用具有已知[0001]方向的块状m面GaN样品通过实验确定了L-PFM相极性关系，进一步表明d压电系数的符号为负。作为生长极性研究的一部分，L-PFM相图像成功揭示了自组装GaN纳米线的面内[0001]取向，并且结果通过扫描透射电子显微镜晶格图像得到了验证。还对两端GaN/AlGaN/GaN纳米线器件进行了电学性质和晶体极性的联合表征，证明L-PFM测量是评估器件整流与极化诱导能带弯曲之间相关性的可行工具。
