Quantification of Si dopant in β-Ga₂O₃-based semiconductor gas sensors by total reflection X-ray fluorescence spectroscopy (TXRF)

Developing of chemical sensors is relevant for solving environmental problems of monitoring the atmosphere of cities and industrial zones. Semiconductor sensors based on metal oxides are a promising type of chemical gas sensors due to their high sensitivity, low cost, small size, and low energy consumption. First attempts of pilot operation of atmospheric air monitoring systems based on such sensors revealed an insufficient stability of their response. Doping silicon in the basic material can solve the problem. At the same time, data on the amount and distribution of the dopant in the material are necessary to determine the relationship «synthesis conditions – composition – properties». We propose an approach to the determination of the composition of novel semiconductor materials based on β-Ga₂O₃ with a silicon dopant content from 0.5 to 2 %at. The approach included grinding of samples using a planetary mill and preparation of suspensions in ethylene glycol, followed by TXRF determination of the analytes on sapphire substrates using the method of absolute contents (Si) with S_r 0.08 and the method of external standard (Ga) with S_r 0.04. X-ray fluorescence analysis of the samples was performed on a S2 PICOFOX spectrometer (Bruker Nano GmbH, Germany). MoKα radiation was used to excite X-ray fluorescence. The spectrum acquisition time is 250 sec. It is shown that the homogeneity of the dopant distribution in the material can be estimated using the suspension analysis. The studied materials demonstrate an irreproducible sensory response which we associated with the revealed inhomogeneity of the silicon distribution over the surface of β-Ga₂O₃.

1. Spirjakin D., Baranov A. M., Somov A., Sleptsov V. Investigation of heating profiles and optimization of power consumption of gas sensors for wireless sensor networks / Sens. Actuators A. 2016. Vol. 247. P. 247 – 253. DOI: 10.1016/j.sna.2016.05.049

2. Collier-Oxandale A., Casey J. G., Piedrahita R., et al. Assessing a low-cost methane sensor quantification system for use in complex rural and urban environments / Atmos. Meas. Tech. 2018. Vol. 11. P. 3569 – 3594. DOI: 10.5194/amt-11-3569-2018

3. Snyder E. G., Watkins T. H., Solomon P. A., et al. The changing paradigm of air pollution monitoring / Environ. Sci. Technol. 2013. Vol. 47. P. 11369 – 11377. DOI: 10.1021/es4022602

4. Krivetskiy V., Efitorov A., Arkhipenk, A., et al. Selective detection of individual gases and CO/H-2 mixture at low concentrations in air by single semiconductor metal oxide sensors working in dynamic temperature mode / Sens. Actuators B. 2018. Vol. 254. P. 502 – 513. DOI: 10.1016/j.snb.2017.07.100

5. Solorzano A., Rodriguez-Perez R., Padilla M., et al. Multi-unit calibration rejects inherent device variability of chemical sensor arrays / Sens. Actuators B. 2018. Vol. 265. P. 142 – 154. DOI: 10.1016/j.snb.2018.02.188

6. Pandeeswari R., Jeyaprakash B. High sensing response of β-Ga2O3 thin film towards ammonia vapours: Influencing factors at room temperature / Sens. Actuators B. 2014. Vol. 195. P. 206 – 214. DOI: 10.1016/j.snb.2014.01.025

7. Raphael R., Anila E. I. Investigation of photoluminescence emission from β-Ga2O3: Ce thin films deposited by spray pyrolysis technique / J. Alloys Compd. 2021. Vol. 872. 159590. DOI: 10.1016/j.jallcom.2021.159590

8. Yan X., He J., Evans D. G., et al. Preparation, characterization and photocatalytic activity of Si-doped and rare earth-doped TiO2 from mesoporous precursors / Appl. Catal. B. 2005. Vol. 55. N 4. P. 243 – 252. DOI: 10.1016/j.apcatb.2004.08.014

9. Niu F., Shao Z. -W., Gao H., et al. Si-doped graphene nanosheets for NOx gas sensing / Sens. Actuators B. 2020. 129005. DOI: 10.1016/j.snb.2020.129005

10. Jang J., Yim H., Choi J. Exploration of Si-doped SnO2 composition and properties of oxide/Ag/oxide multilayers prepared using continuous composition spread by sputtering / Thin Solid Films. 2018. Vol. 660. P. 606 – 612. DOI: 10.1016/j.tsf.2018.05.010

11. Yuan H. Structural, electrical and optical properties of Si doped ZnO films grown by atomic layer deposition / J. Mater. Sci. Mater. Electron. 2012. Vol. 23. N 11. P. 2075 – 2081. DOI: 10.1007/s10854-012-0713-x

12. Brundle C. R., Evans Ch. A., Jr., and Wilson S., Eds. Encyclopedia of Materials Characterization: Surfaces, Interfaces Thin Films. — Greenwich: Manning Publications Co., 1992. — 800 p.

13. Bohlen A. von, Fernández-Ruiz R. Experimental evidence of matrix effects in total-reflection X-ray fluorescence analysis: Coke case / Talanta. 2020. Vol. 209. 120562. DOI: 10.1016/j.talanta.2019.120562

14. De La Calle I., Cabaleiro N., Romero V., et al. Sample pretreatment strategies for total reflection X-ray fluorescence analysis: A tutorial review / Spectrochim. Acta Part B. 2013. Vol. 90. P. 23 – 54. DOI: 10.1016/j.sab.2013.10.001

15. Bonizzoni L., Galli A., Gondola M., Martini M. Comparison between XRF, TXRF, and PXRF analyses for provenance classification of archaeological bricks / X-Ray Spectrom. 2013. Vol. 42. N 4. P. 262 – 267. DOI: 10.1002/xrs.2465

16. Theisen M., Niessner R. Sapphire sample carriers for silicon determination by total-reflection X-ray fluorescence analysis / Spectrochim. Acta Part B. 1999. Vol. 54. N 13. P. 1839 – 1848. DOI: 10.1016/S0584-8547(99)00125-1

17. Klockenkämper R., von Bohlen A. Total-Reflection X-Ray Fluorescence Analysis and Related Methods. 2nd Edition. — Wiley, 2015. — 552 p. DOI: 10.1002/9781118985953

18. Pashkova G. V., Revenko A. G. Determination of elements in water using a total reflection X-ray fluorescence spectrometer / Analit. Kontrol. 2013. Vol. 17. N 2. P. 122 – 140 [in Russian]. DOI: 10.15826/analitika.2013.17.2.001

19. Stepanov S. I., Nikolaev V. I., Bougrov V. E., Romanov A. E. Gallium oxide: properties and applications — A review / Rev. Adv. Mater. Sci. 2016. Vol. 44. N 1. P. 63 – 86.