Nitrogen composition dependence of electron effective mass in GaAs _1-xN_x

We have investigated the N composition, x, and temperature, T, dependence of the electron effective mass, m^*, of GaAs_1-xN _x films with sufficiently low carrier concentration that carriers are expected to be confined to near the bottom of the conduction-band edge (CBE). Using Seebeck and Hall measurements, in conjunction with assumptions of parabolic bands and Fermi-Dirac statistics, we find a nonmonotonic dependence of m^* on x and an increasing T dependence of m^* with x. These trends are not predicted by the two-state band anticrossing model but instead are consistent with the predictions of the linear combination of resonant nitrogen states model, which takes into account several N-related states and their interaction with the GaAs CBE.