Improved ultraviolet photodetection and oxygen gas sensing performance using CeO2 rare-earth oxide thin films deposited on GaN

Abstract

In recent years, high-k dielectric oxide-based metal-insulator-semiconductor (MIS) heterojunctions gain increasing attention due to their potential for dual functionality in ultraviolet (UV) photodetectors (PDs) and gas sensors, offering promising applications in next-generation optoelectronic and sensing technologies. This work presents the fabrication and performance of a vertical Au/CeO₂/GaN heterojunction device for both UV photodetection and oxygen sensing applications. Grazing incidence X-ray diffraction (GIXRD) confirms the formation of cubic-phase CeO₂, while field emission scanning electron microscopy (FESEM) reveals a uniform distribution of CeO₂ clusters on the GaN substrate, indicating a well-developed surface morphology. X-ray photoelectron spectroscopy (XPS) verifies the elemental composition and chemical states of Ce³⁺ and O²⁻. The photodetection properties are evaluated through I-V (dark and UV-illuminated), external quantum efficiency (EQE), detectivity (D∗), responsivity and time-resolved (I-t) measurements. Under 365 nm illumination at 3 V bias, the Au/CeO₂/GaN device post-annealed at 500 °C exhibits a responsivity of 13 A/W, an EQE ranging from 4.8 × 10² to 1.1 × 10³ % and a D∗ of 1.4 × 10¹⁴ Jones. Time-resolved measurements at 0 V show a response time of 80 ms and a recovery time of 480 ms for the 500 °C post-annealed device. For gas sensing, the same heterojunction undergoes exposure to 100 % O₂, 100 % CO₂, 1000 ppm NO and 500 ppm SO₂. The 500 °C post-annealed device demonstrates enhanced sensitivity to oxygen with response values of 0.47, 0.72, 0.77 and 0.82 for 25 %, 50 %, 75 % and 100 % O₂ concentrations, respectively. Time-dependent measurements under 3 V bias yield a response time of 40 s and a recovery time of 47 s. These results confirm the effectiveness of the cost-efficient conventional e-beam evaporation method in producing high-performance CeO₂-based Au/CeO₂/GaN heterojunctions, highlighting their potential for integrated UV photodetection and oxygen gas sensing applications.