Berlin 2005 – scientific programme
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HL: Halbleiterphysik
HL 14: Heterostrukturen
HL 14.3: Talk
Friday, March 4, 2005, 15:30–15:45, TU P-N229
Controlled motion of long-living excitons in tunable potential landscapes — •Andreas Gärtner1, D. Schuh2, and J. P. Kotthaus1 — 1CeNS and Department für Physik der LMU, München — 2Walter Schottky Institut, TU München
The experiments to learn more about externally controlling the dynamics of long-living excitons are carried out in epitaxially grown heterostructures at temperatures below 4K. They contain two GaAs quantum wells (QWs) separated by a thin AlGaAs tunnel barrier. Lithographically patterned superficial gate structures allow the application of electrical fields tunable over a wide range.
An electron-hole pair generated optically usually relaxes quickly into a short-living excitonic state. However, in our QW samples spatially indirect excitons can be induced by an external electrical field: the exciton’s constituents are located in adjacent QWs coupled by the tunnel barrier [1]. Experimentally we observe excitonic life times > 100 ns.
The excitonic energy can be controlled externally by applying electrical fields (quantum confined stark effect). Using adequately patterned metal gate structures various lateral excitonic potential landscapes Eexc(r,t) can be formed causing a force F ∝ ∇ Eexc on an exciton [2]. We experimentally demonstrated excitonic drift over distances of several µm in temporally and spatially varying excitonic potential landscapes.
We also create traps for such long-living excitons by introducing additional superficial SiO2 patters.
[1] Butov et al., Nature 417, 47 (2002)
[2] Zimmermann et al., Phys. Rev. B 56, 13414 (1997)