Optical Hall effect studies on modulation‐doped Al_xGa_1–xAs:Si/GaAs quantum wells

Abstract

We study the temperature (10 K … 293 K) dependence of the optical Hall effect (OHE) in modulationdoped Alx Ga1–x As:Si / GaAs (x = 0.45) superlattice structures with different quantum well thickness (dGaAs = 16.9 nm and dGaAs = 3.7 nm) using generalized magnetooptic ellipsometry at far‐infrared wavelengths. Free electrons are identified within the wells, but not within the doped barriers. The observed OHE can be fully explained within the Drude model and thermionic rate equations. The quantum‐well free electron density (N = 1.3 × 1017 cm–3) increases five times upon sample cooling within the wells with dGaAs = 3.7 nm, and remains constant within the wells with dGaAs = 16.9 nm. We describe this behavior as a steady state of three quantum well electron condensation processes: Coulombactivation of electron states at the Alx Ga1–x As/GaAs interface, quantum‐well‐barrier reservoir interaction, and irreversible electron emission into the host crystal. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)