III-nitride piezotronic/piezo-phototronic materials and devices

Benefiting from the unique non-central symmetric crystal structure, groups II-VI and III-V wurtzite semiconductors, for example, ZnO, AlN, GaN, and InN, possess the piezoelectric property. Carrier behaviors, including generation, transport, separation, and recombination, can be effectively modulated/controlled by piezotronic and piezo-phototronic effects, that control the piezoelectric polarization charges generated at the interface via applying external stress on the polarization orientation of these semiconductors, and then form the piezopotential used as a 'gate' to tune and further improve the performance of semiconductor devices. Based on these advanced properties, a large number of piezotronic and piezo-phototronic devices and applications have been researched, like light emitting diodes, solar cells, sensors, human-machine interfaces, nanogenerators, and so on, and suggest the dramatic improvement of operating efficiency compared to that with no external strain. Moreover, piezotronic and piezo-phototronic effects provide a convenient and economical method to effectively relieve various issues of semiconductor devices, instead of the traditional ways, requiring complicated design, high costs, and a long period of time. This brief review mainly concentrates on the fundamental physical mechanism and correlative devices and applications on emerging piezotronic and piezo-phototronic effects, and wishes to provide scientific guidance on potential functional applications for the future.