The photoluminescence (PL) spectrum of modulation-doped GaAs/AlGaAs quantum wells (MDQW) and heterojunctions (HJ) is studied under a magnetic field (B ) applied parallel to the two-dimensional electron gas (2DEG) layer. The effect of B strongly depends on the electron-hole separation (d eh ), and we revealed remarkable B -induced modifications of the PL spectra in both types of heterostructures. A model considering the direct optical transitions between the conduction and valence subband that are shifted in k-space under B , accounts qualitatively for the observed spectral modifications. In the HJs, the PL intensity of the bulk excitons is strongly reduced relatively to that of the 2DEG with increasing B . This means that the distance between the photoholes and the 2DEG decreases with increased B , and that free holes are responsible for the hole-2DEG PL.

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A comprehensive experimental study of the photoluminescence (PL) spectral evolution under a magnetic field (B ^ 25 T) applied perpendicularly to a high-mobility two-dimensional electron gas (2DEG), is performed on modulation-doped GaAs/AlGaAs heterojunctions at TL=0.3 K. The abrupt transfer of the free exciton to hole-2DEG PL occurring at integer and fractional filling factors is analyzed in a phenomenological model, wherein free excitons photogenerated in the GaAs layer dissociate into a 2D electron and 3D hole near the 2D-electron channel. Such magnetic field induced exciton-(2De-h) transitions are able to explain the remark able strong PL anomalies in single hetrojunctions as compared to those observed in modulation-doped quantum wells.

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We report on microwave (mw) radiation induced electric currents in (Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external in-plane magnetic field. The current generation is attributed to the spin-dependent energy relaxation of electrons heated by mw radiation. The relaxation produces equal and oppositely directed electron flows in the spin-up and spin-down subbands yielding a pure spin current. The Zeeman splitting of the subbands in the magnetic field leads to the conversion of the spin flow into a spin-polarized electric current.

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Sharp, near band gap lines are observed in the reflection and photoluminescence spectra of GaAs/AlGaAs structures consisting of a modulation doped quantum well (MDQW) that contains a high density two-dimensional electron gas (2DEG) and is embedded in a microcavity (MC). The energy dependence of these lines on the MC-confined photon energy shows level anticrossings and Rabi splittings very similar to those observed in systems of undoped QW's embedded in a MC. The spectra are analyzed by calculating the optical susceptibility of the MDQW in the near band gap spectral range and using it within the transfer matrix method. The calculated reflection spectra indicate that the sharp spectral lines are due to k{ parallel}=0 cavity polaritons that are composed of e-h pair excitations just above the 2DEG Fermi edge and are strongly coupled to the MC-confined photons.

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