A far infrared modulated photoluminescence (FIRM-PL) study of cyclotron resonance in a 2D electron gas in GaAs/Al_xGa_1-xAs heterojunctions

The new technique of far infrared modulated photoluminescence (FIRM-PL) has been used to study the properties of a high mobility 2D electron gas in a series of GaAs/AlGaAs heterojunctions. When the occupancy of the lowest Landau level is between 1 and 2 very large transfers of PL intensity are observed at the cyclotron resonance condition. The PL intensity is transferred from the E0 line to E1 corresponding to emission from the first two quantized electric subbands. A study of the power dependence of this signal allows us to deduce that the relative recombination efficiencies of the two lines are around five orders of magnitude different in such structures. This difference leads to a very high sensitivity of this technique for the observation of internal excitations within the electron system.