Observation of intersubband scattering in a 2-dimensional electron system

We observed a strong increase in the low temperature electron scattering rate of a 2-dimensional electron gas in a modulation doped GaAs-(AlGa)As heterojunction at the transition from one-subband to two-subband conduction. Our data provide direct evidence for the occurence of intersubband scattering processes. Electron densities as well as mobilities in each subband are determined separately throughout the transition regime. Mobilities of the ground subband considerably exceed those of the excited subband. All features of the calculated density dependence of the mobilities are qualitatively reproduced by our data.