Elsevier

Thin Solid Films

Volume 618, Part A, 1 November 2016, Pages 73-76
Thin Solid Films

Ultraviolet photodetector and gas sensor based on amorphous In-Ga-Zn-O film

https://doi.org/10.1016/j.tsf.2016.05.013Get rights and content

Highlights

  • UV detector and ozone gas sensor based on InGaZnO4 (IGZO) films were investigated.

  • The properties of the two types of sensors depend on the IGZO thickness.

  • The IGZO films can detect ozone at the ppb level.

Abstract

In this study, amorphous indium gallium zinc oxide (IGZO) thin films with thickness ranges from 13 to 160 nm were deposited on glass. The energy gap of the IGZO measured through transmission spectroscopy was approximately 3.45 eV. When irradiated by ultraviolet (UV) light the transition efficiency (ΔI/Idark) of the 115-nm-thick IGZO films were found approximately as 23,924.

The IGZO thin films were also tested for use as gas sensors. When attached by ozone molecules, the resistance of the film altered as a result of electron transfer from the film to the gas molecules. The fabricated IGZO films can detect ozone to the ppb level. Our results showed that IGZO thin films were capable of sensing both ozone gas and UV light with high sensitivity.

Introduction

Air pollution and excessive ultraviolet (UV) radiation pose significant threats on human health today [1]. Ozone causes physical discomfort, fatigue, dyspnoea, and many other health problems. Extensive exposure to UV radiation is associated with skin cancer and cataract. Therefore, it is important to develop an effective sensor for ozone and UV light detection [2], [3], [4] that can be potentially incorporated into wearable devices. A good sensor is characterized by high sensitivity, long operation time, short reaction time, and low manufacturing cost [5], [6].

Current researches on sensors mainly focus on semiconductors because of their high sensitivity and low cost. There are several examples of ZnO, TiO2, and In2O3 on sensors [7], [8], [9], [10], [11]. In the present study, indium gallium zinc oxide (IGZO) thin films are applied for ozone and UV radiation detection [12]. IGZO is an n-type semiconductor with a bandgap at the UV region of the spectrum and is widely used in the manufacture of liquid crystal panels [13]. In our previous work [14], [15], IGZO thin film deposited at different temperature were used as ozone sensor. The films deposited at room temperature or 200 °C were better. After annealing at 200 °C for 1800 s, the sensitivity of the film improved. In this study, we focused on the sensing potential of IGZO for ozone gas and UV light, including photocurrent and gas response.

Section snippets

Experimental procedure

A 5 mm × 5 mm BK7 glass was chosen as the substrate. BK7 glass is a high quality borosilicate crown optical glass. It provides excellent transmittance light with wavelength from 350 nm to 2000 nm. It is widely used in optical experiment as windows and lenses. The glass substrates were placed sequentially in an ultrasonic bath in acetone, isopropyl alcohol, and methanol for 300 s each. The IGZO thin films were prepared using a radio frequency (RF) magnetron sputtering system targeted with IGZO. The

Results and discussion

Fig. 2 shows the transmittance spectrum of the examined samples. The transmittance spectrum was measured by UV–visible spectrophotometer. The light source of the spectrophotometer was halogen lamp, and photomultiplier tube was used as detector. It could provide wavelength range from 340 nm to 900 nm. The 13-nm-thick sample was almost transparent at the visible light region of the spectrum. The thick films absorbed only a small amount of visible light. The maximum absorption of 163 nm thick IGZO

Conclusion

In our experiment, IGZO films were used to detect UV light and ozone gas. The IGZO thin films exhibited good transition efficiency as light sensors and high sensitivity as ozone gas sensors. The responses of UV and ozone sensor based on IGZO film were obviously affected by the film thickness. A light sensor made of IGZO thin films can detect very low intensity of UV light (186 mW/m2 and still has a good transition efficiency (850). As a gas sensor, it can detect ozone up to a level as low as 300 

Acknowledgement

The authors thank the financial supports of the Ministry of Science and Technology, Taiwan (MOST 104-2112-M-005-005).

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