Novel Al-ZnO/i-ZnO/ZnCo₂O₄ heterojunction design for high-performance ultraviolet photodetectors

Abstract

This work presents the fabrication and investigation of heterojunction devices based on Al-doped ZnO (AZO), intrinsic ZnO (i-ZO), and ZnCo₂O₄ (ZCO) thin films using the spray pyrolysis technique, evaluating their structural, electrical, and optical properties. Hall Effect measurements were used to estimate the depletion widths of the junctions, revealing that the introduction of an intrinsic ZnO interlayer is crucial for controlling the space-charge distribution across a heterojunction. While the AZO/ZCO diode exhibited rectifying behavior without a significant photocurrent under UV irradiation, the AZO/i-ZO/ZCO photodiode demonstrated an enhanced optical response. A maximum photocurrent (32 mA) was observed at 396 nm, corresponding to the fundamental band gap of ZnO, confirming efficient carrier generation and separation. Photocurrent–intensity measurements revealed a linear relationship, validating the device’s sensitivity and reliability as a UV detector. This study demonstrates that inserting an i ZnO layer enables controlled tuning of the depletion region and suppresses interface defects, leading to enhanced UV sensitivity.