Conduction-band-resonant nitrogen-induced levels inGaAs1−xNxwithx<0.03

We report electroreflectance spectra between 1 and 4 eV for ${\mathrm{GaAs}}_{1-x}{\mathrm{N}}_x$ samples with $x<\mathrm{}3\%.\mathrm{}$ In addition to four intrinsic GaAs transitions, three nitrogen-induced optical transitions, $E_{+},$ $E_{+}+{\Delta }_0,$ and $E^{*},$ were observed. The weak and heretofore unknown $E^{*}$ transition was observed in four samples with 0.1 to 2.4 % nitrogen and occurs 0.1 to 0.3 eV below the ∼3 eV intrinsic $E_1$ transition. Opposite to $E_{+}{,E}^{*}$ decreases in energy with increasing nitrogen content. Furthermore, in the dilute limit, both $E_{+}$ and $E^{*}$ appear to converge to the known conduction-band-resonant nitrogen-impurity level ${\mathrm{N}}_x.$