Electro-optic Coefficient Enhancement of Al(x)Ga(1-x)N via Multiple Field Modulations

AlGaN has attracted growing interest for applications in electro-optic devices that generate and process optical signals. To enhance the electric-optic effect with polarity, we designed and grew GaN/AlxGa1-xN quantum structures with x of about 0.5 by metal-organic vapor-phase epitaxy. Spectroscopic ellipsometry measurement and ab initio calculation demonstrated that the stronger polarization fields induced by higher Al contents in the barrier result in larger electro-optic effects. By applying external biases directly on both sides of these quantum structures, a high intensity of external field was achieved, and extraordinary and ordinary refractive indices were characterized by fitting the variable-angle spectroscopic ellipsometry. The values of deduced electric-optic coefficients were significantly enhanced by combining the resonance effect with the internal and external fields. Given the comparable electric-optic coefficients with conventional electro-optic crystals, AlGaN is an attractive candidate for nonlinear optical material, which provides a basis for large-scale integrations of ultraviolet electro-optic devices based on nitride semiconductors.