Nitrogen dependence of the GaAsN interband critical points E-1 and E-1+Delta(1) determined by spectroscopic ellipsometry

The effects of the nitrogen concentrations on the E-1 and E-1+Delta(1) tran sitions of tensile-strained GaAs1-yNy (0.1%less than or equal to y less tha n or equal to 3.7%) grown pseudomorphically to GaAs by metalorganic vapor-p hase epitaxy are studied by spectroscopic ellipsometry. Adachi's critical-p oint composite model is employed for ellipsometry data analysis. Contrary t o the well-known redshift of the band-gap energy E-0, we observe linearly b lueshifted E-1 and E-1+Delta(1) transition energies with increasing nitroge n composition y. For nitrogen compositions of 0 less than or equal to y les s than or equal to 1.65%, the observed blueshift of the E-1 energy is well explained by the sum of the effects of biaxial (001) strain and alloying. ( C) 2000 American Institute of Physics. [S0003-6951(00)02437-2].