Effect of Substrate and Thickness on the Photoconductivity of Nanoparticle Titanium Dioxide Thin Film Vacuum Ultraviolet Photoconductive Detector.

Marilou Cadatal-Raduban,Kohei Yamanoi,Yusuke Horiuchi,Jiří Olejníček,Tomoki Kato,Shingo Ono,Michal Kohout

doi:10.3390/nano12010010

Abstract

Vacuum ultraviolet radiation (VUV, from 100 nm to 200 nm wavelength) is indispensable in many applications, but its detection is still challenging. We report the development of a VUV photoconductive detector, based on titanium dioxide (TiO2) nanoparticle thin films. The effect of crystallinity, optical quality, and crystallite size due to film thickness (80 nm, 500 nm, 1000 nm) and type of substrate (silicon Si, quartz SiO2, soda lime glass SLG) was investigated to explore ways of enhancing the photoconductivity of the detector. The TiO2 film deposited on SiO2 substrate with a film thickness of 80 nm exhibited the best photoconductivity, with a photocurrent of 5.35 milli-Amperes and a photosensitivity of 99.99% for a bias voltage of 70 V. The wavelength response of the detector can be adjusted by changing the thickness of the film as the cut-off shifts to a longer wavelength, as the film becomes thicker. The response time of the TiO2 detector is about 5.8 μs and is comparable to the 5.4 μs response time of a diamond UV sensor. The development of the TiO2 nanoparticle thin film detector is expected to contribute to the enhancement of the use of VUV radiation in an increasing number of important technological and scientific applications.

Highlights

High energy radiation in the vacuum ultraviolet (VUV) region that spans the wavelength range from 200 nm down to 100 nm is indispensable in numerous technological applications, such as surface treatment, photochemical processing, optical cleaning of semiconductor substrates, and sterilization of medical apparatus; in addition, it is crucial for scientific research, primarily in gas chromatography and molecular spectroscopy, for example, to probe carbon–carbon and nitrogen–nitrogen triple bonds in alkynes
We investigate the improvement of its photoconductivity in the VUV region using TiO2 thin films deposited on high resistivity undoped silicon (Si), quartz glass (SiO2 ), and soda lime glass (SLG) substrates with thicknesses of 80 nm, 500 nm, and 1000 nm
Our results show that TiO2 thin films in general—but especially TiO2 thin films deposited on SiO2 substrate with a thickness of 80 nm exhibit higher photoconductivity, with photocurrents reaching the milli-Ampere range, compared with our previous works using wide band gap fluorine-based insulator thin film photoconductive detectors [26,27] and gamma-ray irradiated detectors, based on amorphous TiO2 on SLG substrate [28]

Summary

Introduction

High energy radiation in the vacuum ultraviolet (VUV) region that spans the wavelength range from 200 nm down to 100 nm is indispensable in numerous technological applications, such as surface treatment, photochemical processing, optical cleaning of semiconductor substrates, and sterilization of medical apparatus; in addition, it is crucial for scientific research, primarily in gas chromatography and molecular spectroscopy, for example, to probe carbon–carbon and nitrogen–nitrogen triple bonds in alkynes. The applications of VUV light sources are increasing owing to its higher photon energy compared with the ultraviolet (UV) region, from 400 nm down to 200 nm. Alongside the increasing importance of VUV radiation in various applications, there has been rapid development of VUV light sources [1,2,3]. Various reports focused on the detection of VUV light through scintillation in rare earth-doped wide band gap insulators [4,5,6] and wide band gap semiconductors [7,8,9]. Scintillation relies on the excitation and de-excitation of an activator ion (in rare earth-doped insulators), or the generation and recombination of electron and hole

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