Flexible Transparent ZnO:Al/ZnO/CuAlO x :Ca Heterojunction Diodes on Polyethylene Terephthalate Substrates

Transparent flexible n ⁺-ZnO:Al (100 nm)/n-ZnO (40 nm)/p-CuAlO _x :Ca (100 nm, 200 nm, 300 nm) diodes were fabricated on polyethylene terephthalate substrates at room temperature using a sputtering technique. No additional heat treatment was performed on the fabricated devices. Increase of the diode layer thickness reduced the on-current and leakage-current levels simultaneously, which led the rectification ratio to first increase and then decrease as the p-layer thickness increased. The ultraviolet (UV) response of the diode was also investigated under irradiation at 365 nm. The n ⁺-ZnO:Al (100 nm)/n-ZnO (40 nm)/p-CuAlO _x :Ca (200 nm) diode exhibited photocurrent/leakage current ratio of 1.03 × 10³ and responsivity of 0.64 A/W at reverse bias of ?6 V when measured in flat status. The corresponding photocurrent/leakage current ratio and responsivity were 7.99 × 10² and 0.65 A/W, respectively, for an outwardly bent diode with 5.5 cm radius of curvature. The increases of current levels under bending are attributed to the decreases of series resistance for the diode under tensile strain.