P-type ZnO:N thin films for flexible electronics: The effect of controlled bending cycles on flexible micro-p–n junctions

Herein, the fabrication and characterization of flexible micro-p–n diodes using p-type ZnO:N and n-type ZnO films deposited at room temperature by reactive laser ablation and patterned by photolithography are reported. The p-type layer was deposited with 0.1 sccm O2 and 5 sccm N2 fluxes at 5 mTorr working pressure, ablating a zinc metallic target. In situ x-ray photoelectron spectroscopy revealed 49 at. % zinc, 49 at. % oxygen, and 2 at. % nitrogen in ZnO:N thin films. The electrical properties of the p-type ZnO:N were a hole concentration of 1 × 1018 cm−3, a resistivity of 9 Ω cm, and a mobility of 0.5 cm2 V−1 s−1. The diodes were measured on-plane before and after 10 000 bending cycles (BC) at various curvature radii (RC), showing changes in their electrical properties as a function of both BC and RC. The equivalent circuit analysis of the diodes shows a constant built-in potential (Vbi) of 1.1 V at RC of 11 and 15 mm, after 10 000 BC, consistent with the calculated Vbi derived from the semiconductor layer’s properties (Vbi = 1.09 V). The junctions exhibited a direct/reverse current ratio (ID/IR) up to 6 × 103. A critical RC of 7 mm was identified, below which the diode loses its rectification performance.