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    Photonics Materials Topical Conference Thursday Sessions
       Session PH-ThM

Invited Paper PH-ThM4
Single Quantum Dots as Tunable Artificial Atoms

Thursday, November 1, 2001, 9:20 am, Room 120

Session: Photonic Materials: Studies on the Nano Scale
Presenter: D. Hessman, Lund University, Sweden
Authors: D. Hessman, Lund University, Sweden
M. Holm, Lund University, Sweden
J. Persson, Lund University, Sweden
M.-E. Pistol, Lund University, Sweden
C. Pryor, Lund University, Sweden
L. Samuelson, Lund University, Sweden
Correspondent: Click to Email
We present micro-photoluminescence studies of self-assembled InP quantum dots (QDs) embedded in GaInP. The QDs are pyramid shaped and usually about 15 nm high, with a slightly elongated base of about 40 by 50 nm. There are however also smaller QDs with similar lateral extension but with a considerably smaller height. The change in size is, as expected, accompanied by a change in quantum confinement with a corresponding change in emission energy. In addition, there is a transition from a single sharp emission peak for the smallest dots to several 1 meV broad emission lines emitted over a 50 meV energy range for the largest dots. The reason for this behaviour is unintentional doping in the barrier material, resulting in electron accumulation in the QDs. This gives rise to emission in an energy range corresponding to the energy range occupied by these electrons. Larger QDs accumulate more electrons and thus emit over a larger energy range. For the largest dots, the number of electrons is large enough that Coulomb-induced dephasing sets in, resulting in a dramatic line-width broadening. By depositing a semi-transparent Schottky gate on top of the sample, photoluminescence spectra of single QDs can be obtained as a function of bias. Varying the bias, the number of electrons in a large QD is tuned in the range 0-15. For biases such that only a few electrons are present in the QD, the Coulomb-induced dephasing is reduced and the originally 1 meV broad lines split up into sharp lines. We conclude that InP/GaInP is a very interesting system, with QDs acting as tunable artificial atoms, controllable both by size and external bias.