Berlin 2012 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 84: Quantum Dots and Wires: Transport Properties III (mainly Thermal Gradients)
HL 84.5: Talk
Thursday, March 29, 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 µ2D = 18.3 m2V−1s−1 and a density of n2D = 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).