Nitrogen dependence of the GaAsN interband critical points E1 and E1+Δ1 determined by spectroscopic ellipsometry

The effects of the nitrogen concentrations on the E1 and E1+Δ1 transitions of tensile-strained GaAs1−yNy (0.1%⩽y⩽3.7%) grown pseudomorphically to GaAs by metalorganic vapor-phase epitaxy are studied by spectroscopic ellipsometry. Adachi’s critical-point composite model is employed for ellipsometry data analysis. Contrary to the well-known redshift of the band-gap energy E0, we observe linearly blueshifted E1 and E1+Δ1 transition energies with increasing nitrogen composition y. For nitrogen compositions of 0⩽y⩽1.65%, the observed blueshift of the E1 energy is well explained by the sum of the effects of biaxial (001) strain and alloying.