Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 97: Quantum Dots and Wires: Optical Properties IV (mainly Nitrides)

HL 97.2: Talk

Friday, March 30, 2012, 10:15–10:30, ER 270

Modeling polar exciton-LO-phonon interaction in GaN/AlN quantum dots — •Johannes Settke, Andrei Schliwa, Gordon Callsen, Juri Brunnmeier, Axel Hoffmann, and Christian Thomsen — Institut für Festkörperphysik, Technische Universität Berlin, Germany

Recently, strong exciton-LO-phonon interaction for epitaxial GaN/AlN quantum dots (QD) was observed experimentally by analyzing the LO-phonon sidebands of single-QD excitonic peaks. Depending on the exciton energy, ranging from 3 eV to 4.5 eV, values of the Huang-Rhys parameter S between 0.3 and 0.02 were deduced. Since the polar coupling strength (described by S) for an exciton is proportional to the squared absolute value of the Fourier transformed difference of the probability densities of the electron and hole, S provides a measure for the electron-hole separation.
GaN/AlN QDs are well known for their strong intrinsic piezo- and pyroelectrical fields along the c-axis, giving rise to excitonic charge separation analogous the quantum confined Stark effect. As this charge separation is known to be dependent on the QD height, it should be mirrored by a variation of the parameter S.
Here, we calculate the Huang-Rhys parameter for the ground-state exciton as function of size and composition using a strain dependent 3D implementation of the eight-band k·p model taking into account piezo- and pyroelectric effects in the adiabatic approximation. We discuss the interrelation of QD size, built-in fields, exciton energy, dipole-moment and Huang-Rhys parameter S.