Stress enhanced photoelectric response in flexible AlN single-crystalline thin films

The integration of wide-bandgap (WBG) semiconductors with flexible electronics are anticipated to enhance device performance far beyond the limit of the conventional devices. However, it is challenging to attain robust flexibility and single crystallinity in WBG semiconductors. We fabricated a free-standing AlN film, which can be transferred to any host substrates. Based on this outcome, we further investigated the flexibility of the AlN, as well as the strain-induced properties. It is found that the bending strain can effectively reduce the bandgap of AlN film from 6.2 to 4.8 eV, while no obvious fracture effects after several runs of bent-unbent cycles were observed. Moreover, flexible ultraviolet photodetectors as a platform for exploring the effect of bending stress were demonstrated. The as-obtained photodetector divulges improved responsivity of 161% and a faster rise time response of 31% at a bending radius of 0.5 cm, compared with a control sample. This enhanced performance could originate from the modulation of the bandgap or the piezo-phototronic effect, which influences the migration of carriers during the optoelectronic processes. Our work provides a promising approach for the study of the coupling effect between the flexibility and strain-modulated properties in both WBG semiconductors and devices.