Reduced temperature dependence of the band gap in ${\mathrm{GaAs}}_{1-y}{\mathrm{N}}_y$ investigated with photoluminescence

The effect of the temperature (T) on the band-gap energy ${(E}_g)$ of hydrogenated ${\mathrm{GaAs}}_{1-y}{\mathrm{N}}_y/\mathrm{GaAs}$ quantum wells has been studied by photoluminescence from 10 to 540 K. Nitrogen insertion in GaAs leads to a sizable decrease of $E_g$ and to a flattening of the band-gap dependence on T with respect to that of bare GaAs. Atomic hydrogen irradiation passivates nitrogen in ${\mathrm{GaAs}}_{1-y}{\mathrm{N}}_y$ and leads to an increase of $E_g,$ which is accompanied by an increase in the thermal shrinkage rate (S) of the band gap. Eventually, a strong correlation between S and the concentration of unpassivated N atoms is found. The wide temperature range investigated and the hydrogen induced effects permit to claim that the reduced thermal redshift of the gap in N containing samples: (i) cannot be ascribed to the reduction of the pressure coefficients in Ga(AsN); (ii) can be accounted for, instead, by a cancellation of the Debye-Waller and self-energy terms in the T dependence of the band gap. The latter effect is explained in terms of a recently proposed increase in the localized character of the conduction band edge with increasing N concentration.