A System for Measuring Deep Ultraviolet Cathodoluminescence

Deep ultraviolet (DUV) radiation plays an essential role in several important technologies, including fluorescence, photolithography, and water purification. However, existing methods of producing DUV radiation have limitations: nonlinear processes (such as those used in Nd:YAG lasers) have limited efficiencies because of phase matching requirements and absorption; the efficiencies of state-of-the-art DUV LEDs (typically based on AlGaN) are limited by defects and electron leakage [1]; and mercury-vapor lamps are plagued with health and safety concerns. Scintillation—light emission from transparent materials due to the passage of high-energy particles—could be a viable alternative, particularly if the high-energy particles are electrons (also known as incoherent cathodoluminescence, or ICL). In this case, it has been predicted that direct bandgap emission could be highly efficient compared to the state of the art [2]. Additionally, the emission spectra of scintillators can be tailored by patterning their surfaces with photonic crystals [3], meaning that ICL-based DUV sources could be tunable in ways conventional ones are not. We have built an experimental setup based on a modified scanning electron microscope capable of measuring both ICL and coherent CL in the DUV (&gt; 130 nm). In our setup, the electron beam impinges on the sample at grazing incidence, causing it to emit light. Emission is collected by a DUV coated reflective objective and sent to a UV monochromator and CCD camera, which finally measures the emission spectrum. Our setup has enabled us to measure DUV emission from wide bandgap materials such as diamond and h-BN and can be used to probe samples with patterned surfaces. We anticipate patterning will lead to spectral shaping and enhancement of DUV ICL based on our simulations of an h-BN nanophotonic scintillator, which showed a wavelength-dependent enhancement of the emitted power by nearly three orders of magnitude [3]. Our work enables the advancement of DUV scintillators and highlights the potential of electron beam pumping to lead to more efficient DUV sources, which would be desirable for all the aforementioned applications. This material is based upon work supported by the US Army Research Laboratory and the US Army Research Office through the Institute for Soldier Nanotechnologies under contract W911NF-18-2-0048.<br/><br/><b>References</b><br/>[1] M. Kneissl, J. Rass, Eds., III-Nitride Ultraviolet Emitters (Springer, Cham, 2016).<br/>[2] C. A. Klein, J. Appl. Phys. 39, 2029 (1968).<br/>[3] C. Roques-Carmes, N. Rivera, A. Ghorashi, S. E. Kooi, Y. Yang, Z. Lin, J. Beroz, A. Massuda, J. Sloan, N. Romeo, Y. Yu, J. D. Joannopoulos, I. Kaminer, S. G. Johnson, M. Soljačić, Science 375, eabm9293 (2022).