Observation of a triplet transition in multiple quantum wells

Far-infrared magnetospectroscopic studies of quasi-two-dimensional donor impurity states have been carried out on several GaAs/(Formula presented)(Formula presented)As multiple-quantum-well samples with different doping densities in the barrier with constant sheet doping in the well. Two distinct features on the low-frequency side of cyclotron resonance (CR) were observed. Extensive temperature- and carrier-density-dependence studies combined with statistical calculations of the occupancy of the various possible states have led to the assignment of these features to a (Formula presented) triplet transition (∼13 (Formula presented) lower than CR) and the (Formula presented) transition (∼9 (Formula presented) lower than CR).