The applications of surface plasmons in Ga2O3 ultraviolet photodetector


J W Ritter discovered that certain chemical reactions were catalyzed by exposure to non-visible radiation with a shorter wavelength than violet in 1801. The “chemical rays” found by him were afterwards called ultraviolet radiation. At present, The electromagnetic spectrum of ultraviolet radiation, defined most broadly as 10–400 nanometers, can be divided into a number of spectral regions: UVA (for wavelengths between 400 and 320 nm), UV-B (for wavelengths between 320 and 280 nm), UV-C (for wavelengths between 280 and 200 nm), and far UV (for wavelength between 200 and 10 nm, which reaches the X-ray spectral low energy frontier. UV radiation only accounts for less than 10% of the total solar radiation and most can be absorbed by stratospheric ozone. Although only a few arrives the earth’s surface, this part of UV radiation has a profound impact on the survival and development of humankind and the balance of the ecosystem. Recently, anthropogenic-induced decline in stratospheric ozone concentration, concurrently intensifying the UV radiation, has become alarming, and the ‘ozone hole’ over Antarctica has become larger. So UV detecting and zone monitoring has been the focus of attention and study.
    The research team of professor Qian from State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, devote themselves to the study of wide-band semiconductor beta-Ga2O3 thin film ultraviolet photo-detector. In recent years, Ultraviolet (UV) detectors have wide applications in civil and military areas, such as missile early warning systems, flame detection, environmental monitoring, optical communication and UV radiation calibration and monitoring and so on, so it has attracted considerable research interests. Many kinds of wide bandgap semiconductors, including ZnMgO, diamond, AlGaN, Ga2O3 (α, β, γ, δ, ε) etc., have been developed and applied in fabrication of UV photodetectors. Among these wide bandgap semiconductors, beta-Ga2O3(β-Ga2O3) is particularly suitable for solar-blind photo-detection, due to its wide band gap of ~4.9 eV making it highly transparent from the visible to UV wavelength of 280 nm. In addition, beta-Ga2O3 possesses high chemical and thermal stability. So it has been considered as an attractive and promising material for deep UV photo-detector. Recently, Localized Surface Plasmon Resonance (LSPR) supported by metal nanoparticles provides a new method to enhance the properties of beta-Ga2O3 solar-blind UV photodetector. Noble metal nanoparticles have been widely employed in various optoelectronic devices, but it just achieves LSPR in the visible-infrared region. Besides, aluminum (Al) can excite LSPR from 200 nm to just below 800 nm and its position of the LSPR excitation maximum is sensitive to the size, shape, inter-particle spacing, dielectric environment and dielectric properties of the nanoparticle. So Al is capable of achieving LSPR in the deep ultraviolet region and being applied to deep UV photo-detector. In this work, the effect on both the Al nanoparticles fabricated by rapid thermal annealing and the characteristics of related UV photodetector is investigated. The average particles diameters are 23 nm. The study finds that beta-Ga2O3 based deep UV Photodetector with Al nanoparticles can effectively increase the responsivity and detectivity, as well as reduce the device’s background noise. The main reason is that the increased optical absorption induced by scattering into photo-detector due to the presence of Al nanoparticles. In addition, the enhanced electromagnetic field surrounding the Al nanoparticles accelerates the separation of electron-hole pairs in the surface of beta-Ga2O3 epilayer. Besides, the beta-Ga2O3 surface is passivated by these surface-oxidized Al nanoparticles so that reducing the device’s background noise

The schematic illustration of the MSM solar-blind ultraviolet photodetector

About team
The UV photo-detection technology team coming from State key laboratory of electronic thin films and integrated devices, University of Electronic Science and Technology of China, mainly research wide-band semiconductor materials and fabricating of the related device, which include the grown of beta-Ga2O3 by molecular beam epitaxy and the fabricating of solar-blind UV photo-detector, beta-Ga2O3 based high-voltage power device, as well as amorphous oxide thin film transistor and so on. Our research team members include Professor Liu Xingzhao, Assistant Professor Qian Lingxuan, Doctor Zhang Yiyu and master Shi Xionglin. The team has published over 100 papers in the authorative journals of the relevant area and had one Chinese authorized patent of invention. Moreover, the research team has attained the first prize of the national defense science and technology in 2002, the second prize of the national technological invention in 2003 and the first prize of Ministry of education technology invention in 2005.

Shi X L, Liu H Y, Hou S, et al. The applications of surface plasmons in Ga2O3 ultraviolet photodetector[J]. Opto-Electronic Engineering, 2018, 45(2): 170728.