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HL: Halbleiterphysik

HL 17: Poster Ib

HL 17.42: Poster

Freitag, 4. März 2005, 16:30–19:00, Poster TU F

Anomalous temperature-dependence of free-charge-carrier concentration in modulation-doped Al_xGa_1−xAs/GaAs quantum well superlattices studied by far-infrared magnetooptic Mueller-matrix ellipsometry — •Tino Hofmann¹, Claas von Middendorff¹, Gunnar Leibiger² und Mathias Schubert¹ — ¹Fakultät für Physik und Geowissenschaften, Institut für Experimentelle Physik II, Universität Leipzig, Linnéstraße 5, 04103 Leipzig — ²Fakultät für Chemie und Mineralogie, Halbleiterchemie, Universität Leipzig, Linnéstraße 3, 04103 Leipzig

A study of the temperature-dependent free-charge-carrier properties in modulation-doped Al_xGa_1−xAs:Si/GaAs (L, x = 0.45) superlattices is presented. Two different samples with quantum well lengths L = 18 nm and L = 4 nm are investigated using magnetooptic generalized ellipsometry at far-infrared wavelengths (100−650 cm⁻¹) at external magnetic fields B = ±3 T and temperatures ranging from T = 10 to 293 K. The model analysis allows independent determination of the free-charge-carrier parameters density N, mobility µ and effective mass m within the wells dispensing with the need for electrical contacts. Beside a weak anisotropic mobility behavior, a strong increase of the quantum-well free-charge-carrier density with decreasing temperature is observed for L = 4 nm in contrast to the sample with L = 18 nm where the free-charge-carrier density decreases as expected. A simple rate model successfully describes this behavior as a steady state of three condensation processes.