Highly Sensitive Direct‐Conversion Vacuum Flat‐Panel X‐Ray Detectors Formed by Ga2O3‐ZnO Heterojunction Cold Cathode and ZnS Target and their Photoelectron Multiplication Mechanism

Abstract

AbstractX‐ray detectors are significantly applied in medical diagnoses, industrial inspections, and scientific researches, but the detection sensitivity is limited by the material, device structure, and detection mechanism. This article proposes a direct‐conversion flat‐panel X‐ray detector formed by Ga2O3‐ZnO heterojunction cold cathode and ZnS target to achieve highly sensitive X‐ray detection. The field emission efficiency of Ga2O3‐ZnO heterojunction cold cathode is improved by optimizing the spacing between the adjacent circular pattern in patterned ZnO nanowire arrays. The electron–hole pairs generated by X‐ray photons are multiplied in ZnS target by the electron bombardment induced photoconductivity effect, resulting in a high internal gain (1 × 104%) and a high X‐ray detection sensitivity (7.1 × 102 μCGyair−1 cm−2) for 6 keV X‐ray at 9.2 V μm−1 electric field. In addition, the proposed detector has low dark current density (50 pA mm−2 at 9.2 V μm–1 electric field), good stability (0.2% fluctuation for 60 s), and fast response speed (rise time: 5.3 ms) owing to a built‐in electric field in Ga2O3‐ZnO heterojunction, a ballistic electron transportation in vacuum gap, and a high resistance in ZnS thin film.