Berlin 2005 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 7: Transporteigenschaften

HL 7.9: Vortrag

Freitag, 4. März 2005, 12:45–13:00, TU P-N226

Separating X-valley electrons in AlAs using quantum point contacts — •F. Erfurth, J. Moser, M. Bichler, D. Schuh, G. Abstreiter, and M. Grayson — Walter Schottky Institut, TU-Muenchen, 85748 Garching

We demonstrate the fabrication of one-dimensional (1D) AlAs electron systems used to distinguish between electrons from different conduction band valleys. Split gates are used to create a quantum point contact (QPC) by depleting two-dimensional (2D) electrons in a 15 nm wide quantum well ( n = 3 × 10¹¹ cm⁻², µ = 5.8 m²/Vs). In AlAs, the conduction band X -valley mass is anisotropic ( m_x = 0.19 m₀ , m_y = 1.1 m₀) and doubly degenerate. This degeneracy can be broken at a QPC depending on the QPC alignment relative to the crystal axes. The lateral confinement causes splitting into distinct mass subbands, and by shifting the 1D Fermi level, electrons from a specific valley can be selectively transmitted.
In our experiments we first use a magnetic field to break the valley degeneracy. At the quantum Hall filling factors of ν = 2 , B = 6 T we are able to separate edge channels into one transmitted valley and one reflected valley channel. At ν=3, B=4 T ( ν = 4 , B=3 T) all three (four) channels of alternating valleys can be successively separated. This demonstrates the first successful use of 1D constrictions to distinguish between electrons from different valleys.