The line shape of electromodulation in uniform electric field of delta-doped GaAs has been calculated and compared with the experiments. The calculations show that the Franz-Keldysh oscillations (FKO) beats observed in experiments are contributed form the interference of heavy-hole and light-hole transitions. The calculations also show that the linear equation of extrema is a good approximation to analyze the electric field from the FKO line shape, although the equation only considers the heavy-hole transition.
