Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 84: Quantum Dots and Wires: Transport Properties III (mainly Thermal Gradients)

HL 84.5: Vortrag

Donnerstag, 29. März 2012, 16:00–16:15, EW 202

Phonon-drag thermopower of a Si/SiGe quantum point contact — •Joeren von Pock¹, Daniel Salloch¹, Ulrich Wieser¹, Ulrich Kunze¹, and Thomas Hackbarth² — ¹Lehrstuhl für Werkstoffe und Nanoelektronik, Ruhr-Universität Bochum, D-44780 Bochum — ²DaimlerChrysler Forschungszentrum Ulm, D-89081 Ulm

We investigate the influence of phonon-drag thermopower on a gate-modulated inertial ballistic rectifier. Our devices are fabricated from a high mobility Si/SiGe heterostructure with an electron mobility of µ_2D = 18.3 m²V⁻¹s⁻¹ and a density of n_2D = 6.3· 10¹⁵ m⁻² at 1.4 K. The confinement is realized by low damage CF₄/O₂ plasma etching. Two quantum point contacts (QPCs) are directed parallel and perpendicular to a heating wire and are electrically isolated from it. A gradient of temperature from the heating wire generates phonons which drag electrons through QPC constriction. In case of the perpendicular QPC the electrons relax behind the constriction and create a measurable thermopower signal of about 10⁻³ times smaller magnitude than hot-electron thermopower. Because of the absence of a gradient of temperature on each side of the constriction, the QPC parallel to the heating wire shows no signal. The measured phonon-drag thermopower is strongly dependent on the phonon priority direction [100] in Si/SiGe. The temperature dependence shows a decrease of the phonon-drag induced thermopower in the region of 4.2 K ≤ T ≤ 30 K which is not yet understood. At 1.5 K no phonon-drag effect is observed as in [1].
[1] W. E. Chickering et al., PRL 103, 046807 (2009).