Abstract
Material parameters in nitride semiconductors are still controversial. Previously reported values are highly scattered and several parameters have yet to be experimentally deduced. Furthermore, the quasicubic approximation has been conventionally used although its quantitative validity has not been supported. Herein, we performed reflectance spectroscopy under uniaxial stress for nonpolar and semipolar GaN and AlN bulk substrates. All the excitonic deformation potentials were experimentally determined for the first time, and we found that the quasicubic approximation breaks in GaN and AlN.
