Defect engineering of second-harmonic generation in nonlinear optical semiconductors

Second-harmonic generation (SHG) plays a key role in developing modern optical devices and quantum optics, as they can expand the wavelength range provided by common laser sources. Conven-tionally, the modulation of SHG in nonlinear optical (NLO) materials heavily depends on various external effects. In this article, by devel-oping the basic rules that comprise the interplay between defects and the SHG effect, we propose an alternative strategy to intrinsi-cally regulate the SHG of NLO materials via defect engineering, which is feasible via controlling the growth conditions. Using first -principles calculations, we demonstrate that the SHG susceptibility of KBe2BO3F2 (KBBF), the only available deep-ultraviolet NLO mate-rial with a weak SHG effect, can be dramatically enhanced by nearly one order of magnitude under specific growth conditions. This is comparable to many other famous narrow-band gap NLO crystals. In general, our developed basic rules and material demonstration could be extended to other NLO systems.