Decoding Glamorous Piezoelectricity and Pyroelectricity of Truncated Tapered GaN Nanowires: A Bond Relaxation Insight

From the notion of atomic bond relaxation, an analytical correlation for position-, size-, and shape-dependent piezoelectric/pyroelectric potential of truncated tapered GaN nanowires is developed. Quantitative analyses have uncovered that surface broken bond-motivated atomic coordination number lowering, bond shortening and hardening, and surface-to-volume ratio rising are common physical origins of position, size, and shape effects of piezoelectric/pyroelectric potential. The position, size, and shape dependencies of piezoelectric potential are equal to those of pyroelectric potential. Concretely, the piezoelectric/pyroelectric potential ratio shows marked strengthening with the change in position from bottom to top of truncated tapered nanowires, while those of traditional columnar nanowires are independent of position. Piezoelectric/pyroelectric potential is bottom radius- and half cone angle-dependent, which rises with decreasing bottom radius in a hyperbolic form and rises with increasing half cone angle in a slightly nonlinear way. The truncated tapered nanowires can produce much higher piezoelectric/pyroelectric potential than their columnar nanowire counterparts owing to their larger surface-to-volume ratio. At the same equivalent bottom radius, with the decrease in the number of sides for truncated tapered polygonal nanowires, the surface-to-volume ratio rises, and the piezoelectric/pyroelectric potential heightens. The present formulation goes beyond the range of existing methods, which not only unveils quantitative information but also displays a penetrative perception of mechanisms for piezoelectric/pyroelectric potential in response to position, size, and shape.