UV–Visible silicon detectors with zinc oxide nanoparticles acting as wavelength shifters

Abstract

Broad spectral response of photon detectors without cryogenic cooling is of great interest in many fields of application like spectroscopy and high-energy particle physics. In order to achieve broad spectral range, different approaches can be found in literature. One approach is the multijunction detector incorporating different kind of absorbers. The drawback here is the fabrication cost as well as complicated fabrication technique [1]. Another approach is the application of wavelength shifters which absorb the UV light and re-emit it in the lower energy range which preferably matches the peak sensitivity of the detector. The application of chemical wavelength shifters like e.g. Tetraphenyl Butadiene (TPB) has been reported, but they posses some drawbacks like instability in contact with some substances and photo-degradation behavior [2]. There is also a concept of the application of luminescent nanoparticles on top of the detector, which act as wavelength shifters [3]. This approach has several advantages such as little interference in the detector structure (even the UV-blocking window of the detector does not pose a problem), straightforward deposition technique and large possibility of adjustment of the spectral regions depending on the kind of the nanoparticles. Thanks to the quantum confinement related to small size of the particles, the bandgap of the material can be engineered, therefore the absorption and emission properties of the material can be tuned. Other feature which has an impact on the emission and excitation properties are the defects, which can act as luminescent centers. The wavelength shifters considered for this application are two kinds of commercially available zinc oxide (ZnO) nanoparticles. The differences between them lay in the size and the structural quality, which influence their optical properties like emission and excitation spectra as well as photoluminescence quantum yield. For the application they are distributed in the poly (methyl methacrylate) – PMMA - matrix and spin-coated on the detector window. The work consists of the analysis of the parameters of the zinc oxide nanopowders only as well as the nanopowders dispersed in the PMMA matrix. The problem has been investigated both theoretically and experimentally. The experimental part involved examination of the samples deposited on the laboratory glass and finally on the photodetector. Apart from the kind of zinc oxide nanoparticles, the technological parameters which were optimised was the concentration of ZnO in PMMA as well as thickness of the layer. Two types of photodetectors have been considered for modification: silicon photodiodes with broad spectral response from 190 nm to 1000 nm and Multi Pixel Photon Counters (MPPC) sensitive in the range 270 – 900 nm. These latter ones are used for sophisticated applications as well as single-photon detection. The comparison of parameters of the detectors before and after modification is shown. 1.Gessert, T.A., Colegrove, E., Stafford, B., Kodama, R., Gao, W., Moutinho, H.R., Kuciauskas, D., Reedy, R.C., Barnes, T.M., Sivananthan, S. MRS Advances, 1 (50), pp. 3391-3402 (2016) 2.Alvarez, V. et al., Journal of Instrumentation 7, P02010 (2012) 3.Sahi, S., Magill, S., & Ma, L., Xie, J., Chen, W., Jones, B., Nygren, D., Scientific Reports. 8:10515, (2018)