Determining the polarity of droplet epitaxy grown AlGaN nanorods using piezoresponse force microscopy

Al0.97Ga0.03N nanorods are grown by the plasma-assisted molecular beam epitaxy technique under extreme group III rich condition. Droplet epitaxy process is employed for the formation of well-faceted nanorods with smooth morphology. We report the polarity of Al0.97Ga0.03N nanorods oriented in different crystallographic directions by the non-destructive technique of piezoresponse force microscopy (PFM). The phase formation is investigated by the Raman spectroscopic analysis. Spatial distribution of piezoresponse of Al0.97Ga0.03N nanorods is mapped, and the polarities of the different crystalline planes of m and c are determined. The corresponding piezoresponse is explained on the basis of spontaneous polarization in a unit cell of the hexagonal crystal, which is further confirmed using piezoresponse spectroscopy. Piezoelectric coefficient (d33) is measured to be ∼9.0 ± 1 pm/V in Al0.97Ga0.03N nanorods using the PFM technique.