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. Conventionally, the modulation of SHG in nonlinear optical (NLO) materials heavily depends on various external effects. In this article, by developing the basic rules that comprise the interplay between defects and the SHG effect, we propose an alternative strategy to intrinsically 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 material 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.