Toward Quantitative Measurements of Piezoelectricity in III-N Semiconductor Nanowires

Piezoelectric semiconductor III-nitride nanostructures have received increasing interest as an alternative material for energy harvesters, sensors, and self-sustainable electronics, demanding further clarification of their piezoelectric behavior. Despite the feasibility of piezoresponse force microscopy (PFM) to resolve piezoresponses at the nanoscale, several difficulties arise when the measurements are performed on low piezocoefficient materials due to various artifacts. This work shows that semi-quantitative PFM on low piezocoefficient III-nitrides can be achieved in high-aspect-ratio nanostructures, such as nanowires or nanorods. For conventional bulk and thin films, accurate determination of their piezoresponses is limited because of clamping and bending effects which can occur simultaneously during PFM measurements. While the clamping effect only reduces the piezoresponse amplitude, the bending motion either increases or decreases this amplitude and can also rotate the phase by 180°. Improved electric field distribution in nanowires minimizes both artifacts, allowing correct determination of crystal polarities and piezocoefficients. In contrast to the reports in the literature, we do not observe giant piezoelectricity in III-N nanowires with a diameter in the range of 30-80 nm. This work provides an access to fundamental parameters for developing III-N-based piezoelectric nanodevices.