JTu3A.31.pdf FiO/LS 2014 © OSA 2014 Humidity Sensing Using SbSI Nanophotodetectors Krystian Mistewicz, Marian Nowak, Piotr Szperlich, Andrzej Nowrot Solid State Physics Section, Institute of Physics - Center for Science and Education, Silesian University of Technology, Krasinskiego 8, 40-019 Katowice, Poland Author e-mail address: krystian.mistewicz@polsl.pl Abstract: This paper shows usability of antimony sulfoiodide (SbSI) nanowires as photo- conductive humidity sensors. Qualitatively different photoconductivity transient characteristics for low, and high humidity have been observed. Desorption of H 2 O from SbSI nanowires surface is reported. OCIS codes: (040.5160) Photodetectors; (160.4236) Nanomaterials; (260.5150) Photoconductivity 1. Introduction Nowadays, we can observe great demand for low power humidity sensors. Due to the large surface-to-volume ratio, nanomaterials are appropriate candidates for gas sensors. Adsorption of molecules at surface of nanomaterial influences substantially its electrical properties. The antimony sulfoiodide (SbSI) is a semiconducting [1] ferroelectric with Curie temperature T C = 292 K [2]. Strong influence of water vapor on the AC electrical response of SbSI gel made up of large quantity nanowires has been studied in [3]. Recently [4], the examination of SbSI gel in ferroelectric phase as photoconductive humidity sensor and photodetector has been performed. The aim of the present paper is to investigate photoelectric properties of SbSI gel over the Curie temperature to explore its application as a humidity sensor. 2. Experiment, Results and Discussion SbSI gel was produced sonochemically according to technology described in [5]. The sample was cut from SbSI xerogel into cuboid with following dimensions: 5.70(1) mm × 6.5β(1) mm × γ.45(1) mm. The smallest opposite surfaces of the sample were covered with silver paste (SPI Supplies). 0 20 40 60 0,0 0,1 0,2 0,3 0,4 I PC , nA t, min a 0 20 40 60 -2 0 2 I PC , nA t, min b Fig. 1. Photoconductivity transient characteristics of SbSI gel in (a) dry N2 (RH = 2%) and (b) moist N2 (RH = 49%). Experiment conditions: T = 304 K; p = 4∙10 4 Pa; E = 3 kV/m; λ = 488 nm; I0 = γ.1∙10 21 photon/(m 2 s). Arrows indicate moments, when illumination was switched on (↑) and switched off (↓). Red solid curves represent the best fitted dependences described by Eq. (1). Electric measurements were performed in nitrogen at pressure p = 4∙10 4 Pa. Different humidities were maintained by passing the N 2 to the test chamber over water in special container. The humidity was determined using HIH-40003 sensor (Honeywell) with Keithley 196 multimeter. In order to control temperature of the sample Pt-100 sensor was placed near to the investigated SbSI gel and connected to the 211 temperature monitor (Lake Shore). The photoconductivity transient characteristics were registered using Keithley 6517A electrometer. Argon laser (model Reliant 50s, Laser Physics) with wavelength λ = 488 nm was employed for sample illumination. Shape of photoconductivity transient characteristic depends essentially on the value of relative humidity (RH). For low humidity (Fig. 1a) positive photoconductivity is observed. I PC increases monotonically after illumination switching on and drops monotonically after illumination switching off. Rise of photocurrent due to illumination switching on is caused by photogeneration of excess carriers. When illumination is switched off, recombination of the excess carriers occurs and it results in reduction of photocurrent. For RH higher than critical value RH C ≈ 44%