Suppression of geometric induced artifacts in piezoresponse force microscopy of III-N semiconductor nanowires.

This work presents systematic investigations of piezoresponse force microscopy (PFM) on III-N semiconductors. In bulks and thin films, the electrostatic artifacts in the PFM signal were minimized by using a stiff cantilever and a top metallic electrode. Depending on the electrode geometry, the clamping and bending effects can concurrently occur. While the clamping effect only decreases the piezoresponse amplitude, the bending one can either increase or decrease the amplitude and; if it is dominant, the phase signal becomes rotating by 180{\deg}. The reduced lateral dimension of the nanowires can suppress both artifacts by homogenizing the field distribution. The phase of the piezoresponse from GaN, Al0.9Ga0.1N/GaN, and AlN nanowires is always coherent with their polarity, and the extracted d33 values agree with their respective bulk ones. We suggest that the nanowire is a relevant geometry to perform quasi-quantitative PFM, and there is no giant piezoelectric in this type of nanowires as claimed in the literature.