Effect of Pd functionalization on optical and hydrogen sensing properties of ZnO: Eu films

Abstract

ZnO: Eu films have been functionalized with Pd nanoparticles of sizes (5–15 nm) synthesized by a chemical solution approach. Morphological and optical characterizations were carried out using SEM and transmission spectroscopy. The effects of Pd functionalization on the ZnO: Eu columnar microstructures have been investigated by analysing the photo response, photoresponsivity, external quantum efficiency (EQE), detectivity, and carrier dynamics rate. The Pd functionalized ZnO: Eu films (Pd40/ZnO: Eu) show a higher photo response (∼33), about three times higher compared to bare ZnO: Eu films (∼12.4) at 100 ℃. This can be explained by photocarrier transfer from the ZnO conduction band to the Fermi level of PdO and electron trapping on the sensing surface due to oxygen adsorption. A remarkable EQE and detectivity were found for both sample sets, Pd40/ZnO: Eu (∼930 %, ∼2˟1013 Jones) and ZnO: Eu (∼2030 %, ∼1.71˟1013 Jones). High UV–visible rejection ratio (R280 nm/R443 nm) of ∼82 is found, indicating good spectral selectivity. The effect of irradiance on photoresponsivity and recovery time has also been investigated and shows that increasing irradiance leads to an increase in electron-hole pair generation at a faster rate, contributing to higher photoresponsivity and faster recovery. Pd-functionalization results in higher gas sensing response of ∼15 and improved selectivity to 100 ppm hydrogen at lower operating temperatures for Pd40/ZnO: Eu films. The proposed columnar microstructures may enable advanced photodetector applications at relatively low bias voltage (∼50 mV). In this work, the importance towards Pd functionalization for H2 gas sensing and UV detection is presented.