The anomalous bandgap bowing in GaAsN

Abstract

The composition dependence of the fundamental bandgap of thin, pseudomorphic GaAs1−xNx layers (0⩽x⩽5%) on GaAs substrates is studied by optical transmission measurements and high resolution x-ray diffraction. We present a very large set of consistent experimental data. An empirical double exponential composition dependence of the bowing parameter is obtained. This expression accurately describes the measured bandgaps, and allows estimations for higher N incorporations. The bowing parameter reaches 40 eV for very low N incorporations (x≈0.1%), and strongly decreases with increasing N molar fraction. We estimate that the bowing parameter would reach a constant value of 7.5 eV for x≳8%, as in an alloy. This bowing would not be sufficient to close the bandgap for higher N incorporations.