Ultrahigh UV responsivity of single nonpolar a-axial GaN nanowire with asymmetric piezopotential via piezo-phototronic effect: Dependence of carrier screening effect on strain

Here, we report on the ultrahigh UV responsivity of 1.3×10⁵ (A/W) on a single nonpolar a-axial GaN nanowire (NW) based metal-semiconductor-metal (M-S-M) UV photodetector (PD), incorporating the piezo-phototronic effect. An exceptional enhancement of 160% from 5×10⁴ to 1.3×10⁵ (A/W) in the UV responsivity when applying a 0.012% tensile strain is achieved. To the best of our knowledge, this is the best performance gained from a single GaN NW PD without employing additional surface treatment. Moreover, an extraordinary phenomenon in the output current is observed showing that the UV responsivity reaches the maximum only at an optimum applied strain and then falls off. This new nonlinear phenomenon is further verified by showing the shift of the maximum UV responsivity toward the higher tensile stress with increasing carrier concentration, through comprehensive analysis on the dependence of the carrier screening effect on both the strain-induced Schottky barrier height (SBH) effect and gating effect, induced by the unique asymmetric piezopotential distribution in a strained a-axial GaN NW. Therefore, this work provides a new design rule for better utilizing piezopotential in coupling with light to achieve the highest performance in optoelectronic devices incorporating piezo-phototronics.