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.