Abstract

Al_xGa_1−xN is a direct-gap III-V material system whose band gap (3.6 eV for x = 0 and 6.2 eV for x = 1) and refractive index (2.52 for x = 0 and 2.2 for x = 1) can be tuned with alloy composition.¹ Because of the highly ionic nature of the Al, Ga, and N bonds, Al_xGa_1−xN is expected to possess high nonlinear optical coefficients, e.g., for second-harmonic-generation (SHG) and the electro-optic effect. The commonly used material for integrated electro-optic modulators, LiNbO₃, suffers from photorefractive damage and increased transmission loss for visible (blue-green) and near-UV applications. Therefore use of the electro-optic effect and waveguiding in GaN epitaxial layers opens up possibilities for integrated-optic modulators for this short-wavelength regime. Previous measurements on the SHG coefficients indicate nonlinear optical coefficients higher than those of KDP and quartz.^2,3 This paper reports what we believe to be the first measurement of the electro-optic effect in GaN and demonstrates preliminary waveguide measurements in single-crystal GaN films.

© 1995 Optical Society of America