Elektron-Phonon Wechselwirkung in Halbleiter Nanostrukturen

Als zentrale Fragestellung wird die Elektron-Phonon Wechselwirkung, hauptsächlich in Nitrid-Einzelquanten-punkten, untersucht.Dazu werden nanoskopische Methoden wie spitzenverstärkte Ramanspektroskopie, Kathodolumineszenz-Spekroskopie imTransmissionselektronenmikroskop, örtlich- und zeitaufgelöste Photo- und Kathodolumineszenzspektroskopie in Verbindung mitKreuz- und Autokorrelation Experimenten ausgenutzt. Diese einmalige Kombination von hochentwickelten spektroskopischenMethoden ermöglicht es uns, die Elektron-Phonon Wechselwirkung mit einer örtlichen Auflösung besser als 20 nm (5 nm)nachzuweisen. Als Anwendungspotenzial werden Nitrid-Raumtemperatur-Einzelphotonenemitter und Laser im ultravioletten
Spektralgebiet charakterisiert.

Electron-Phonon Interaction in Semiconductor Nanostructures

The main focus of A6 is a deeper understanding of the interaction between the electronic and the phononic
system that governs the device performance of nitride based nanostructures. Our approach is a unique
combination and correlation of nanoscopic methods like tip-enhanced Raman spectroscopy (TERS), μPhotoluminescence (μPL), and scanning transmission electron microscopy (STEM) with Cathodo-luminescence(CL) capability. This phalanx of complementary, advanced spectroscopic techniques enables us to investigatethe electron-phonon coupling with unmatched spatial resolution, providing not only insight into devicelimitations, but also a fundamental understanding of carrier relaxation and dephasing processes.
With TERS we analyze how the tip-induced electric field and the plasmonic coupling between the metal tip
and the (doped) sample influence the Raman signature depending on the carrier concentration. Such measurementsare not only of importance for studying localized phonons in, e.g. nanowires (NWs) and singlequantum dots (QDs), but also for understanding the nature of the enhancement process itself. Hence, TERSis most valuable for the interpretation of μPL and CL results, directly reflecting the coupling between theelectronic and phononic states. Based on our combination of ultraviolet (UV) enhanced μPL and CL, bothproviding the capability for ps time-resolved and correlation spectroscopy, we identify, e.g. single-photonemitters in nitride QDs paving the way towards efficient single- and two-photon emitters. The exceptionallystrong coupling between e.g. excitons and phonons in nitride nanostructures even fosters the generation ofsingle, confined phonons, exploring new device concepts at the interface of photonics and phononics based on single phonon emission and storage. Our recent discovery of hybrid-quasiparticles with unconventionaltotal spin numbers is fundamentally related to phonon-induced spin flip process of carriers benefitting fromsizeable coupling constants in especially nitride-based quantum dots.