Fast switching characteristics of (111) oriented cerium oxide thin film-based metal-oxide semiconductor UV photodetector

Abstract

This work presents the studies of cerium oxide (CeO2) thin films (TFs) with different thicknesses on Si substrates using the electron beam evaporation method for photodetector (PD) application in the UV region. The effect of thickness on the structural, morphological, and optoelectronic properties of the TF was comprehensively studied. The structure and crystallinity of the samples were characterized by x-ray diffraction and all TFs showed highly preferred orientation along the (111) plane. The crystallinity and structural parameters like crystallite size, lattice constant, microstrain and dislocation density were also calculated, and 200 nm film showed the best results. Field emission scanning electron microscopy revealed that the CeO2 TF was smoothly deposited on the substrate. The absorption enhanced with increased thickness and thereby, the bandgap energy decreased to 3.45 eV for 300 nm as compared to 3.65 eV for 100 nm thickness. The electrical performance also proved superior for thicker films with increased photocurrent accompanied by lower dark current. The 200 nm CeO2 TF device showed the fastest switching response with a rise time of 240 ms and a fall time of 152 ms at a bias voltage of −4 V with an on/off ratio of 13.59. Moreover, spectral responses were higher for 200 nm film, thus exhibiting good PD performance. It is believed that this work will be highly useful for use as a sensitive UV PD.