Absolute transmission, reflection, and absorption studies in GaAs/AlAs quantum wells containing a photoexcited electron gas

A study is presented of the absolute reflection, transmission, and absorption of several undoped mixed type-I-type-II GaAs/AlAs multiple quantum wells at T=2 K. These structures consist of alternating GaAs narrow and wide wells separated by AlAs barriers. They are designed so that a two-dimensional electron gas (2DEG) is photogenerated in the wide wells. The density of this gas is varied in the estimated range of 0≤(Formula presented)≤3×(Formula presented) by varying the photoexcitation intensity in the range of 0≤(Formula presented)≤100 mW/(Formula presented). In the presence of a 2DEG the (e1:hh1)1S and (e1:lh1)1S excitonic transitions broaden and weaken with increasing (Formula presented), but their energy is virtually unchanged. The reflection and transmission spectra are analyzed by assuming a Lorentzian oscillator response function for the excitonic transitions and a broadened step function for the free-carrier (e1-hh1) and (e1-lh1) bands. Fitting the calculated optical spectra to the experimental ones (both line shape and absolute intensity) yields the dependence of the following parameters on (Formula presented): exciton energies, exciton-photon interaction strength, exciton damping, and the onset energy of the free e-h interband transitions. It is found that the interaction strength of the (e1:hh1)1S and (e1:lh1)1S excitons with photons decreases and their damping increases with increasing (Formula presented).