Evidence of valence band perturbations in GaAsN/GaAs(001): A combined variable-angle spectroscopic ellipsometry and modulated photoreflectance investigation

The contribution of the fundamental gap E_ as well as those of the E_ + Delta(so) and E+ transitions to the dielectric function of GaAs1-xNx alloys near the band edge were determined from variable-angle spectroscopic ellipsometry and modulated photoreflectance spectroscopy analyses. The oscillator strength of the E_ optical transition increases weakly with nitrogen incorporation. The two experimental techniques independently reveal that not only the oscillator strength of the E+ transition but also that of E_ + Delta(so) become larger compared to that of the fundamental gap as the N content increases. Since the same conduction band is involved in both the E_ transition and its split-off replica, these results reveal that adding nitrogen in GaAs1-xNx alloys affects not only the conduction but also the valence bands.