Dresden 2006 – scientific programme
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HL: Halbleiterphysik
HL 41: Heterostructures
HL 41.5: Talk
Thursday, March 30, 2006, 12:00–12:15, BEY 154
Resonant impurity states in quantum wells and superlattices — •Dominik Stehr1, Claus Metzner2, and Manfred Helm1 — 1Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, P.O. Box 510119, D-01314 Dresden — 2Technische Physik I, Universität Erlangen, Erwin-Rommel-Str.1, D-91058 Erlangen
Introducing dopant atoms in quantum wells (QWs) and superlattices results in a random impurity potential in addition to the confinement in growth direction. As has recently been demonstrated, their hydrogenic levels form resonant states attached to each QW subband and finally develop into a novel type of impurity band in the case of superlattices[1].
Here we present detailed numerical studies of coupled double and quadruple QW structures with relatively low doping (few 1010cm−2 per layer), which can be seen as precursors to superlattices. By treating impurity and QW potential in a unified framework we exactly diagonalize the fully three-dimensional Schrödinger equation and calculate the infrared absorption spectrum. We find that, by varying the lattice temperature, the absorption spectrum changes dramatically, not only in its energetic resonances but also in its electronic origin. Analyzing the 3D-wavefunctions of the electronic states contributing to the final absorption spectra shows that at room temperature mainly delocalized states (intersubband states) contribute to the spectra, whereas at low temperature they are dominated by strongly localized states (impurity states). Hitherto unexplained experimental data of a quadruple QW sample are nearly perfectly reproduced by our calculation.
[1] D. Stehr et al., Phys. Rev. Lett., in print (2005).