Enhanced hot-electron injection across Au/GaN heterojunction by the piezo-phototronic effect for efficient sub-bandgap photodetection

Performances of plasmon mediated optoelectronic devices are mainly limited by the hot carrier injection efficiency in metal-semiconductor plasmonic heterojunctions. Herein, the piezo-phototronic effect was used to promote hot-electron injection in Au/GaN plasmonic heterojunction, and the dynamics of hot-electron transport were investigated. The lateral and vertical Au/GaN plasmonic heterojunction devices were fabricated based on freestanding GaN film. The comparisons of hot-electron transport behaviors and photoresponse performances between lateral and vertical Au/GaN plasmonic heterojunction devices for sub-bandgap photodetection were systematically investigated. The photoresponse current of vertical heterojunction device is three orders of magnitude higher than lateral heterojunction device owing to the shortened electron transport path. The height of Schottky barrier at the heterojunction interface was tuned by the piezo-phototronic effect to enhance the injection efficiency of hot-electron. Optimized by the piezo-phototronic effect, the photoresponse current increases by nearly 89% under an applied compressive strain of 0.57% and the hot-electron injection efficiency was increased from 37.50% to 90.45%. The manipulating dynamic transport process of hot-electron under the regulation of applied strain is further confirmed by using transient absorption (TA) spectral measurement. This work provides a new architecture for efficient sub-bandgap photodetection based on GaN, and provides insight into the hot-electron dynamics in metal–semiconductor heterostructures.