Crystallographic polarity measurements in two-terminal GaN nanowire devices by lateral piezoresponse force microscopy∗ ∗Contribution of an agency of the U.S. government; not subject to copyright

• Published in: Nanotechnology Vol. 31; no. 42
• Main Authors: Brubaker, Matt D, Roshko, Alexana, Berweger, Samuel, Blanchard, Paul T, Little, Charles A E, Harvey, Todd E, Sanford, Norman A, Bertness, Kris A
• Format: Journal Article
• Language: English
• Published: IOP Publishing 16.10.2020
• Subjects: crystallographic polarity; GaN Nanowires; piezoresponse force microscopy
• ISSN: 0957-4484; 1361-6528
• 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 d33 piezoelectic coefficient, the L-PFM measurements in this study were implemented on horizontally oriented nanowires that coupled to shear deformations through the d15 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 d15 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/Al0.1Ga0.9N/GaN nanowires devices, demonstrating L-PFM measurements as a viable tool for assessing correlations between device rectification and polarization-induced band bending.