Crystallographic Polarity Measurements in Two-Terminal GaN Nanowire Devices by Lateral Piezoresponse Force Microscopy
Matthew Brubaker, Alexana Roshko, Samuel Berweger, Paul T. Blanchard, Todd E. Harvey, Norman A. Sanford, Kris A. Bertness
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  direction and further indicated that the sign of the d15 piezoelectric coefficient was negative. L-PFM phase images successfully revealed the in-plane  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.
, Roshko, A.
, Berweger, S.
, Blanchard, P.
, Harvey, T.
, Sanford, N.
and Bertness, K.
Crystallographic Polarity Measurements in Two-Terminal GaN Nanowire Devices by Lateral Piezoresponse Force Microscopy, Nanotechnology, [online], https://doi.org/10.1088/1361-6528/ab9fb2
(Accessed November 29, 2023)