Abstract
A hybrid film consisting of zinc oxide nanoparticles (ZnO NPs) and carbon nanotubes (CNTs) is formed on a glass substrate using a simple and swift spin coating process for the use in ultraviolet photodetectors (UV PDs). The incorporation of various types of CNTs into ZnO NPs (ZnO@CNT) enhances the performance of UV PDs with respect to sensitivity, photoresponse, and long-term operation stability when compared with pristine ZnO NP films. In particular, the introduction of single-walled CNTs (SWNTs) exhibits a superior performance when compared with the multiwalled CNTs (MWNTs) because SWNTs can not only facilitate the stability of free electrons generated by the O2 desorption on ZnO under UV irradiation owing to the built-in potential between ZnO and SWNT heterojunctions, but also allow facile and efficient transport pathways for electrons through SWNTs with high aspect ratio and low defect density. Furthermore, among the various SWNTs (arc-discharged (A-SWNT), Hipco (H-SWNT), and CoMoCat (C-SWNT) SWNTs), we demonstrate the ZnO@A-SWNT hybrid film exhibits the best performance because of higher conductivity and aspect ratio in A-SWNTs when compared with those of other types of SWNTs. At the optimized conditions for the ZnO@A-SWNT film (ratio of A-SWNTs and ZnO NPs and electrode distance), ZnO@A-SWNT displays a sensitivity of 4.9 × 103 % with an on/off current ratio of ~104 at the bias of 2 V under the UV wavelength of 365 nm (0.47 mW/cm2). In addition, the stability in long-term operation and photoresponse time are significantly improved by the introduction of A-SWNTs into the ZnO NP film when compared with the bare ZnO NPs film.
Highlights
Ultraviolet (UV) photodetectors (PDs) have drawn much attention because of their wide range of applications such as UV monitoring in the environment, flame sensing, missile launch detection, biological sensing, and space communications [1,2,3]
We demonstrate that ZnO@A-single-walled CNTs (SWNTs) exhibits the best performance in terms of sensitivity, photoresponses, and reproducibility in long-term operation when compared with those of other ZnO@carbon nanotubes (CNTs) hybrid films and pristine zinc oxide nanoparticles (ZnO NPs) films
We demonstrated a high-performance ultraviolet photodetectors (UV PDs) using the ZnO@arc-discharged SWNTs (A-SWNTs) hybrid film prepared via a facile and fast spin coating process
Summary
Ultraviolet (UV) photodetectors (PDs) have drawn much attention because of their wide range of applications such as UV monitoring in the environment, flame sensing, missile launch detection, biological sensing, and space communications [1,2,3]. ZnO-based PDs are promising candidates as alternatives for silicon-based PDs because n-type ZnO semiconductors allow an intrinsic visible-blindness (associated with a direct large band gap of 3.3 eV) and room-temperature operation They have the advantages of simple synthetic methods, excellent chemical stability, and environmental friendliness [9,10,11,12,13,14]. The photocurrent generation mechanism is regulated by this O2-mediated free-electron generation when ZnO is used standalone as an active material in UV PD devices regardless of the morphology of and synthetic process for ZnO In this mechanism, the electronegative O2 molecules adsorbed on ZnO surface can be desorbed upon UV light because of the charge neutralization by the generated holes, resulting in the free electrons on ZnO. These types of devices generally suffer from a poor sensitivity (low on–off ratio) and photoresponse behavior (a long rise and decay time) that is associated with the instability of free electrons which can recombine with holes that have not been completely paired with electronegative O2 and slow O2 adsorption/desorption processes, respectively [27]
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