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The terahertz radiation in GaAs/AlGaAs quantum wells with different types of doping was experimentally studied under interband optical excitation of nonequilibrium charge carriers. The structures doped only with donors, and the structures with a high degree of compensation of donors by acceptors were studied. The spectra of terahertz radiation associated with charge carrier transitions with the participation of shallow impurity states were obtained and analyzed. It was shown that the compensation of donors by acceptors leads to a significant increase in the intensity of terahertz photoluminescence. The spectra of near-infrared photoluminescence with the participation of donor and acceptor states were also studied and analyzed. [ABSTRACT FROM AUTHOR]

Terahertz emission in GaAs/AlGaAs quantum well structures doped with shallow impurities was studied in conditions of interband optical excitation for n-doped structures and impurity breakdown in the lateral electric field for p-doped structures. Emission spectra were obtained. It was shown that the observed emission is related to optical transitions of charge carriers between impurity levels and to impurity-band transitions. The depopulation of the final states under interband optical pumping was realized with recombination of non-equilibrium holes and electrons localized at neutral donors. [ABSTRACT FROM AUTHOR]

Optical phenomena in quantum dot and quantum well nanostructures aimed at the development of mid-infrared lasers based on intraband electron transitions are investigated in the conditions of interband optical pumping. Evolution of photoluminescence spectra and interband light absorption with intensity of interband optical excitation is investigated in InAs/GaAs quantum dot structures. Optically induced intersubband mid-infrared light absorption is studied in undoped tunnel-coupled GaAs/AlGaAs quantum wells. The stabilization of the electron concentration at the ground level of tunnel-coupled quantum wells under increasing pumping level is established. [ABSTRACT FROM AUTHOR]

The Γ[sub 2]-X[sub z1] intersubband dynamics in GaAs/AlAs quantum-well structures is investigated by time-resolved infrared pump and probe experiments. In the studied structure, the second Γ level in GaAs is nearly resonant to the first X[sub z] level in AlAs, resulting in elastic Γ-X scattering. A biexponential behavior of ground-state recovery has been found with a time constant in the order of 1 ps for the Γ[sub 2]-Γ[sub 1] relaxation and a time constant of 7 ps (at 10 K), which represents the X[sub z]-Γ[sub 2] transfer. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The circular photogalvanic effect (CPGE) has been observed in (100)-oriented p-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It is shown that monopolar optical spin orientation of free carriers causes an electric current which reverses its direction upon changing from left to right circularly polarized radiation. CPGE at normal incidence and the occurrence of the linear photogalvanic effect indicate a reduced point symmetry of studied multilayered heterostructures. As proposed, CPGE can be utilized to investigate separately spin polarization of electrons and holes and the symmetry of quantum wells. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]