Spectroscopy of quasi-2D D^- ions in the presence of excess electrons

Far infrared magneto-spectroscopic studies of quasi-2D D^- ions have been carried out in several GaAs Al_0.3Ga_0.7As MQW samples with a wide range of controlled doping in the barrier with constant sheet doping in the well. Temperature, carrier density dependence, and polarization studies of a new confinement-related feature on the low frequency side of cyclotron resonance indicate that this feature is likely due to a D^- triplet transition. The temperature dependence of the relative absorption strength of D^-, D⁰ and CR were also studied and found to be in qualitative agreement with a calculation that includes the probability of both single and double occupancy (the D^- states) of a particular donor site in thermal equilibrium in high magnetic field.