Theory of electron mobility in dilute nitride semiconductors

The scattering of n-type carriers by three types of nitrogen-associated states (single substitutional N atoms, N–N pairs, and hydrogen passivated N defects) is investigated for the dilute nitride alloy GaNxAs1−x. The connection between the band gap bowing and carrier mobility is derived as a function of temperature and nitrogen concentration. The scattering by substitutional N atoms has been shown to be proportional to the square of the derivative of the band-edge energy with respect to N concentration. In unpassivated samples, the presence of N–N pairs is found to modify the electron mobility by no more than 10%, compared to a model in which scattering by all N atoms is treated independently, in the relevant range of temperatures and N concentration. The temperature dependence of the GaAs conduction band edge gives rise, in conjunction with resonant scattering from weakly temperature-dependent N levels, to an unusually small temperature variation in the defect contribution to carrier mobility. A clear signature of N passivation is predicted to be a simultaneous increase of the band gap and of the carrier mobility.