Strain-Induced Photocurrent Enhancement in Photodetectors Based on Nanometer-Thick ZnO Films on Flexible Polydimethylsiloxane Substrates

Strain-induced modulation of electronic, magnetic, and photonic properties provides additional functionalities to oxide thin film-based electronics as compared to those of conventional rigid electronics. Herein, we introduce a simple transfer process for highly crystalline nanometer-thick films onto flexible polydimethylsiloxane (PDMS) using water-soluble sacrificial NaCl crystals. The c axis of the high-temperature sputtered ZnO thin films grew along a parallel direction to the substrate surface, thereby revealing the (100) reflection on both Si and NaCl substrates, which is desirable for designing photoconductors with a planar geometry. However, films grown at room temperature showed a preferred growth orientation along the vertical direction to the substrate surface. The photodetectors synthesized using ZnO thin films grown directly on PDMS at room temperature exhibited a low current, whereas the photodetectors fabricated using ZnO thin films grown at a high temperature exhibited dramatically increased currents in the dark and under ultraviolet (UV) light. The photodetector performance was further enhanced under external strain due to the piezophototronic effect induced by bending or stretching the photodetectors under UV light. These properties were confirmed by the absorption or desorption of oxygen on the ZnO surface under the applied strains. The proposed strain-induced optoelectronic property modulation of highly crystalline ZnO thin films is promising for the development of future multifunctional flexible, transparent, and wearable electronics.