Transport relaxation time and quantum lifetime in selectively doped GaAs/AlAs heterostructures

Low-temperature dependences of the transport relaxation time ($\tau_{tr}$) and quantum lifetime ($\tau_{q}$) on the density of the two-dimensional electron gas ($n_{e}$) in GaAs quantum wells with AlAs/GaAs lateral superlattice barriers have been studied. An exponential increase in the quantum lifetime with increasing electron density has been observed. It has been shown that the sharp increase in the quantum lifetime correlates with the appearance of X electrons in the AlAs/GaAs lateral superlattice barriers. It has been established that the ratio of the transport relaxation time to the quantum lifetime in the studied structures nonmonotonically depends on the density: the ratio $\tau_{tr}/\tau_{q}$ first increases linearly with $n_e$ and then decreases. This behavior is not described by the existing theories.