Alloy Engineering of a Polar (Si,Ge)₂N₂O System for Controllable Second Harmonic Performance

Although silicon oxynitrides are important semiconductors for many practical applications, their potential second-order nonlinear optical (NLO) regardless of balanced or controllable performance, have never been systemically explored. Using the first-principles calculations, in this article, we discover that sinoite (i.e., typical oxynitride Si2N2O) can simultaneously exhibit wide bandgap, strong second-harmonic generation (SHG) effect, and large birefringence, which further confirmed by our preliminary experimental data. Importantly, propose alloying engineering be applied to control NLO properties Si2N2O system. Combining calculations cluster expansion theory, demonstrate Ge into easily form low formation energy Si2(1-x)Ge2xN2O alloys, turn achieve phase-matching harmonic output with high SHG efficiency at different ranges. Therefore, alloy could provide a unique approach effectively performance Si2(1-x)Ge2xN2O, making polar system holding applications tunable laser frequency conversion all-optical devices.