III-Nitride Based Narrow Band Far-UVC LEDs for Airborne and Surface Disinfection
Authors: Bui Ha Quoc Thang , Velpula Ravi Teja , Jain Barsha , Nguyen Hieu Pham Trung 
Published: December 2020

Narrow-band far-ultraviolet C (200-230 nm) light-emitting diodes (far-UVC LEDs) are strongly detrimental to bacteria and viruses while minimally invasive to human health can be used at human-occupied spaces as a disinfectant to suppress the outbreak of infectious diseases. Here, we investigated a design for a narrow band far-UVC LED with a center wavelength222 nm based on AlGaN nanowires. The LED achieves an ultra-narrow full width at half maximum (FWHM) of ~12 nm after an introduced metal-dielectric Fabry-Perot optical bandpass interference filter with three periods of (Al/MgF2/Al). This narrow-band far-UVC LED is a promising candidate for airborne surface disinfection to prevent the spread of contagious diseases such as COVID-19.

AlGaN nanowires have emerged as a promising candidate for highly efficient UV LEDs due to low threading dislocations, reduced polarization [1, 2], effective strain relaxation, and nearly-free quantum-confined Stark effects [3], compared to thin-film UV LEDs. Herein, using Advanced Physical Models of Semiconductor Devices (APSYS), we numerically demonstrate a far-UVC LED structure. It consists of 300 nm n-AlN/ 40 nm i-AlGaN/ 100 nm p-AlN/ 20 nm p-Al0.95Ga0.05N on a silicon(111) substrate, shown in Figure 1(a). The active region is an Al0.855Ga0.145N single quantum well. Moreover, for efficient airborne surface disinfection, a narrow spectrum is required to effectively trigger biological events for avoiding harmful effects. Toward that end, a far-UVC LED at 222 nm for surface disinfection is preferred because this wavelength is almost harmless to the human body since it is entirely absorbed at the dead skin cell layer [4].

Figure 1(b) presents the narrow electroluminescent spectrum of the far-UVC LED, achieved by the APSYS simulation. The peak emission is at 222 nm with FWHM of ~12 nm. However, the experimentally-obtained far-UVC spectrum from LEDs may be broad, FWHM of larger than 12 nm. Thus, we use OpenFilter [5] to design a 222 nm band-pass filter as a back-up approach for the narrow emission spectrum. Starting with a typical metal-dielectric Fabry-Perot interferometer of three (Al/MgF2/Al) stacks, the layers’ thickness is optimized. A relatively high achieved transmission of up to 50% with a FWHM of ~12 nm is shown in the inset of Figure 1(b). Therefore, the proposed nanowire far-UVC LEDs are substantial potential for disinfection applications [6].

In conclusion, the AlGaN nanowire structure presents a novel and remarkable design for high-efficiency far-UVC LEDs which offer a chemical-free, and convenient approach to disinfection applications in human-occupied spaces, with a negligible health concern.

References:

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[4] D. Welch, M. Buonanno, V. Grilj, I. Shuryak, C. Crickmore, A. W. Bigelow, G. R. Pehrson, G. Johnson & D. J. Brenner, "Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases" Scientific Reports, vol. 8, pp.1-7, 2018

[5] S. Larouche and L. Martinu, "OpenFilters: open-source software for the design, optimization, and synthesis of optical filters," Applied Optics, vol. 47, pp. C219-C230, 2008.

[6] W. Kowalski, Ultraviolet germicidal irradiation handbook: UVGI for air and surface disinfection. Springer science & business media, 2010.

Figure 1