Barrier D ? complexes in a high-mobility two-dimensional electron system

The cyclotron excitation spectrum of selectively doped AlGaAs/GaAs quantum wells with a high (up to 2 × 10⁷ cm²/(V s)) mobility of electrons has been studied by means of the Raman scattering. The lines of the Raman scattering by the excitations of D ^? complexes, the objects in which two electrons localized in a quantum well are coupled to a charged impurity in a barrier, have been detected and identified. Spin-singlet D ^? complexes have been shown to exist in the entire range of the electron filling factor, from v → 0 to v = 2, owing to the specificity of the Coulomb interaction in two-dimensional systems. The excitation energies of the singlet D ^? complexes have been studied as functions of the electron density, quantum well width, and magnetic field.