Optical properties of GaAs/sub 1-y/N/sub y/ (y/spl les/0.037)

Abstract

The optical properties of MOVPE GaAs/sub 1-y/N/sub y/ (0/spl les/y/spl les/3.7%) single layers and GaAsN/GaAs superlattices are studied using spectroscopic ellipsometry and Raman spectroscopy. We analyse the dielectric function near the critical points E/sub 0/, E/sub 1/ and E/sub 1/+/spl Delta//sub 1/ using Adachi's critical-point model. For the layers and the GaAsN superlattice sublayers we observe the strong reduction of the band gap. Contrary to the red shift of the gap energy E/sub 0/, the E/sub 1/ and E/sub 1/+/spl Delta//sub 1/ energies are linearly blue shifted with increasing y. For 0/spl les/y/spl les/1.65% the observed blueshift of the E/sub 1/ energy is well explained by the combination of the effects of biaxial [001] strain and alloying. In the Raman spectra the redshift and broadening of the GaAs LO/sub 1/ mode and the existence of the nitrogen local mode LO/sub 2/ near 470 cm/sup -1/ have been detected.