Low temperature infrared measurements and photo-induced persistent changes of intersubband transitions in GaAs/AlGaAs multiple quantum wells

Utilizing infrared absorption and Hall measurements, a detailed study is presented of the temperature dependence (10 K smaller than T smaller than 300 K) of the intersubband transition and related doping behaviour in GaAs/Al0.32Ga0.68As multiple quantum well structures with Si doping concentrations between 1 x 10 high 18 cm high -3 in the quatum wells. The intersubband transition frequency increases with decreasing temperature, which can be adequately modelled by considering the different effective masses and the thermal populations of the two electron subbands. This model also accounts for the decrease in linewidth of the infrared absorption resonance upon cooling. In Hall measurements a persistent photo-induced decrease in the free electron concentration within the GaAs quantum wells is observed for Si doping levels exceeding 5 x 10 high 18 cm high -3. Corresponding decreases are observed both in the integrated absorption and the absolute frequency of the intersubband transition, the latter arising from a reduction in the depolarization shift. The spectral dependence of the photo-induced changes over the energy range 1.2 eV smaller than ev smaller than 2.5 eV, along with thermal regeneration over the temperature range 70 K smaller than T smaller than 150 K, have been studied.