High-detectivity near-infrared photodetector based on Ag 2 S nanocrystals Hossein Roshan a , Fereshte Ravanan a , Mohammad Hossein Sheikhi a, * , Ali Mirzaei b a Department of Communication and Electronics Engineering, School of Electrical and Computer Engineering, Shiraz University, Shiraz, 51154-71348, Iran b Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz, 71557-13876, Iran article info Article history: Received 10 April 2020 Received in revised form 12 August 2020 Accepted 29 August 2020 Available online 2 September 2020 Keywords: Ag 2 S Near-infrared Photodetector abstract Infrared detection is a key point in optoelectronic systems and thus has attracted considerable attention in recent years. In this paper, a novel, heavy metal-free, and low-cost near-infrared photoconductor based on Ag 2 S nanocrystals (NCs) was realized for the first time. Ag 2 S NCs were synthesized by a facile chemical synthesis method at room temperature and were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and optical absorption. The photoconductor was fabricated by drop-casting Ag 2 S NCs on the interdigitated electrodes which were designed on a printed circuit board. The fabricated photodetector was able to work with a very low bias voltage of 0.05 V. Device performance was evaluated in terms of photosensitivity, responsivity, and detectivity under 750, 850, and 940 nm wavelengths illuminations. The fabricated photodetector exhibited a high detectivity of 2.7  10 10 (more than 10 9 Jones) under 750 nm wavelength illumination at room temperature. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Infrared light is an invisible light that shows many desirable applications in different areas due to its low attenuation in prop- agating media. This spectrum can be divided into three regions; near-infrared (NIR, 0.75 mme2.5 mm), middle infrared (MIR, 2.5e25 mm) and far-infrared (FIR, 25e1000 mm). NIR detectors are highly desirable in many applications including optical telecom- munication systems [1], wireless systems for short-range com- munications [2], health monitoring systems [3,4], infrared imaging in medicine [5,6], biosensors [7], optical gas sensing [8], photo spectroscopy [9], and passive night visions [10]. Infrared detection requires highly sensitive photodetectors with low noise. Mercury cadmium tellurium (HgCdTe) and indium gal- lium arsenide (InGaAs) have been traditionally employed for IR photodetectors [11]. These conventional detectors are very sensi- tive and robust. Nonetheless, complex procedures are needed for fabrication of such detections. Also, they contain heavy metals such as Hg and toxic materials such as Cd and As, that are highly dangerous for human beings [12]. Moreover, they are incompatible with silicon and flexible polymer substrates due to the lattice mismatch considerations. On the other hand, the nanoparticle (NP)-based photodetectors which are fabricated by low-cost chemical synthesis methods have attracted considerable attention for the development of high per- formance photodetectors. Not only they show higher performance than the conventional photodetectors but also they show high compatibility with silicon and flexible substrates. Thanks to the advantages of nanostructured materials, they show a higher ab- sorption coefficient, higher carrier lifetime, and lower dark current, relative to their bulk counterparts. Metal chalcogenides and metal dichalcogenides are categorized in semiconducting materials with tunable bandgap energies [13e15]. They have used as the sensing materials in resistive-based sensors [16e19], photovoltaic devices [20e22], and light-emitting devices [23,24]. Besides, different kinds of narrow bandgap metal chalcogenides such as PbS, PbSe, PbTe, CdTe, HgTe, are used in infrared detection applications due to their excellent optical properties [25e27]. Although these semiconductors are widely used in realization of high performance NIR photodetectors, they contain toxic elements and heavy metals including Pb, Cd, Hg, As, and Te. Progressive concerns about the toxicity of these compounds necessitate employing of nontoxic and environmentally friendly materials in infrared photodetector applications. In this regard, silver chalcogenides with low toxicity, narrow bandgaps, and high infrared absorption properties could be used for realization of infrared detectors [28,29]. * Corresponding author. E-mail address: msheikhi@shirazu.ac.ir (M.H. Sheikhi). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2020.156948 0925-8388/© 2020 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 852 (2021) 156948