Piezophototronic\nEffect Enhanced Flexible Tunneling\nDevices by Separating the Photosensitive Layer and the Piezoelectric\nModulation Layer

The piezo-phototronic effect uses the piezoelectric potential/piezoelectric\ncharge generated by the piezoelectric semiconductor material to regulate\nthe energy band structure and photogenerated carrier behavior at the\ninterface/junction, thereby modulating the device’s performance.\nThe positive/negative piezoelectric charges generated at the interface\nof piezoelectric semiconductors can reduce the electron/hole barriers\nand thus enhance the transport of photogenerated carriers. However,\nelectron/hole potential wells are formed when the electron/hole potential\nbarrier caused by positive/negative piezoelectric charges is lowered\ntoo much, hindering the transport of photogenerated carriers. It is\ndifficult to balance the relationship between potential barriers and\npotential wells while introducing the piezo-phototronic effect. In\nthis work, a physical mechanism by separating the photosensitive layer\nand the piezoelectric modulation layer is proposed to deal with the\nabove-mentioned issue in flexible tunneling devices. The piezoelectric\nmodulation layer is solely used to adjust the electron/hole barriers,\nwhile the photosensitive layer is used to absorb photons and generate\nphotogenerated carriers. This avoids the limitation on the transport\nof photogenerated carriers caused by potential wells in the piezoelectric\nsemiconductor, thereby significantly increasing the adjustable range\nof the barriers. Experimental results show that the photoresponsivity\nof the flexible p-Si/Al<sub>2</sub>O<sub>3</sub>/<i>n</i>-ZnO tunneling device is optimized from 5.5 A/W to 35.8 A/W by the\npiezo-phototronic effect after separating the piezoelectric charges\nand photogenerated carriers. In addition, finite element analysis\nis used to simulate the influence of piezoelectric charges on the\nenergy bands to corroborate the accuracy of the theoretical mechanism\nand experimental results. This work not only presents an optoelectronic\ndevice with excellent performance but also offers novel guidance for\nimproving the performance of optoelectronic devices using the piezo-phototronic\neffect.