Optimized photoresponse performances in vertical and horizontal photodetectors based on freestanding GaN membranes

GaN has become an important material in the optoelectronics due to its suitable band gap and excellent physical and chemical properties, however, the grown substrates limit device geometry owing to their poor electrical and thermal conductivity. Herein, horizonal and vertical GaN ultraviolet photodetectors (UV PDs) were fabricated using the freestanding GaN membranes obtained by an epitaxial lift-off technique. The photoresponse behaviors in the fabricated PDs were then optimized by the piezo-phototronic effect. Owing to the synergistic effect of spontaneous polarization and asymmetric electrodes, the vertical UV PD exhibits unique self-powered characteristics with the light on/off of 3.3 x 103 and the responsivity (R) of 114 mA/W at the bias of 0 V. Optimized by the piezo-phototronic effect, the R increases to 168 mA/W at a tension strain of 0.25 %. In comparison, the R of horizontal UV PD decreases, regardless of the compression or tension. Physical mechanisms of the performances optimization in the vertical and horizontal UV PDs are proposed and analyzed. This study opens a pathway to fabricate GaN UV PDs with different device configurations and provides fundamental support for their performance modulation by the piezo-phototronic effect. (c) 2023 Elsevier B.V. All rights reserved.