High performance ZnO quantum dot (QD)/ magnetron sputtered ZnO homojunction ultraviolet photodetectors

Abstract

The performance of photodetectors can be simultaneously determined by the photoinduced carrier generation and transportation, and thereby a huge challenge still remains for the fabrication of ultra-sensitive ZnO UV due to the irreconcilable contradiction between high crystallinity and additional adsorption–desorption sites. Here, we demonstrate ZnO quantum dot (QD) / magnetron sputtered ZnO homojunction photodetectors with an excellent performance by systematically varying the thickness ratios between two ZnO layers. With the well-balanced ratio, ZnO QDs offers extra adsorption–desorption sites owing to the increased surface defects, and accelerated carrier transportation is concurrently achieved with the highly crystallized magnetron sputtered ZnO layers. As a consequence, the responsivity and external quantum efficiency of the ZnO homojunction photodetector fabricated at 250 ℃ radically increased to ∼ 551 mA/W and 195.4% under 350 nm light illumination (8.58 mW cm−2) at the bias of 10 V. Depending on the annealing temperature, the responsivity of the ZnO homojunction photodetector is further increased to ∼ 1.3 A/W at 450 ℃ even with an identical ratio on account of the improved crystallinity, which paves the path to overcome the hindrance for the ultra-sensitive UV photodetection.