Contents lists available at ScienceDirect Optik journal homepage: www.elsevier.com/locate/ijleo Original research article Hydrothermally synthesized zinc oxide nanoparticle based photodetector for blue spectrum detection H. Ahmad a,b , M. Tajdidzadeh a , K. Thambiratnam a, ⁎ , M. Yasin b, ⁎ a Photonics Research Centre, University of Malaya, 50603 Kuala Lumpur, Malaysia b Dept. of Physics, Faculty of Science and Technology, Airlangga University, 60115 Surabaya, Indonesia ARTICLE INFO Keywords: Photodetector Hydrothermal synthesis Zinc oxide nanoparticles ITO glass Blue light ABSTRACT A photodetector, based on zinc oxide nanoparticles (ZnO-NPs) is designed and fabricated using the drop casting method. Two glass slides coated with Indium tin oxide (ITO) thin films ap- proximately 2.5 μm thick are used as source and drain electrodes, together with Schottky contacts fabricated with ZnO-NPs for the efficient transfer of photo-generated charge carriers. The pro- posed photodetectors showed significant sensitivity under white light emitting diode (LED) il- lumination at 468 nm, which is near the blue light spectrum. The current–voltage (I–V) char- acteristics of the proposed photodetectors indicate the generation of electron-hole pairs under white LED illumination at 265 μW, and stable photocurrent is achieved at high direct current (DC) bias voltages. Photodector response and recovery times of approximately 66.52 and 134.36 μs respectively are obtained at LED frequency modulation of 100 Hz at a bias voltage of 5 V. This represents an enhancement of the capabilities of ZnO-NPs, which is typically used for detection in the UV region only. 1. Introduction Photodetectors based on wide band-gap materials such as ZnO, SiC and GaN are capable of enhancing sensitivity in the ultraviolet (UV) spectra region [1–3]. Among these materials, ZnO nanostructures in particular are advantageous due to their inherent char- acteristics such as quantum confinement, reduced dark current, increased absorption efficiency and potential for large area and lower cost devices [4]. ZnO has a wide direct band gap of ∼3.37 eV at room temperature and a large exciton binding energy of 60 meV which is sensitive to the UV region [5–7] and is thus a promising material for a wide range of applications such as varistors [8], transistors [9], solar cells [10], sensors [11], and UV-photodetectors [12–15]. As a result of this, the use of ZnO as a base material for photodetectors has seen significant interest and uptake, with numerous works using ZnO as a photosensitive elements component of these devices [16,17]. In this regard, metal–semiconductor-metal (MSM) photodetectors comprise of two interdigitated metal contacts on top of a semiconducting two dimensional (2D) material [18]. In comparison to common PIN photodiodes of similar size, the active region’s dark current is reported to be lower than in MSM photodetectors due to interdigitated electrodes, making them good candidates for high speed photodetection [18–21]. Schottky diodes and MSM photodetectors based on ZnO nanostructures have also been suc- cessfully demonstrated in the UV region [22]. Therefore, higher performance MSM-UV photodetectors can be realized through improvised crystal quality so as to obtain significantly larger Schottky barrier heights at the metal–semiconductor interface. A large barrier height results in less leakage of current and an enhancement in responsivity, which can be obtain using metals with high work https://doi.org/10.1016/j.ijleo.2018.07.002 Received 29 January 2018; Received in revised form 27 April 2018; Accepted 1 July 2018 ⁎ Corresponding authors. E-mail addresses: kavintheran@gmail.com (K. Thambiratnam), yasin@fst.unair.ac.id (M. Yasin). Optik - International Journal for Light and Electron Optics 172 (2018) 35–42 0030-4026/ © 2018 Elsevier GmbH. All rights reserved. T