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

The contribution of the fundamental gap ${\text{E}}_{\ensuremath{-}}$ as well as those of the ${\text{E}}_{\ensuremath{-}}+{\ensuremath{\Delta}}_{\text{so}}$ and ${\text{E}}_{+}$ transitions to the dielectric function of ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}(001)$ alloys were determined from variable-angle spectroscopic ellipsometry and modulated photoreflectance spectroscopy analyses. The oscillator strength of the ${\text{E}}_{\ensuremath{-}}$ optical transition increases weakly with nitrogen incorporation. The two experimental techniques independently reveal that the oscillator strength of the ${\text{E}}_{\ensuremath{-}}+{\ensuremath{\Delta}}_{\text{so}}$ transition becomes larger compared to that of the fundamental gap as the N content increases. Since the same conduction band is involved in both the ${\text{E}}_{\ensuremath{-}}$ transition and its split-off replica ${\text{E}}_{\ensuremath{-}}+{\ensuremath{\Delta}}_{\text{so}}$, this result reveals that adding nitrogen in ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}(001)$ alloys affects not only the conduction but also the valence bands.