Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 96: Ultrafast Electron Dynamics at Surfaces and Interfaces

O 96.3: Vortrag

Freitag, 20. März 2015, 11:15–11:30, MA 004

Charge Transfer Dynamics at the Buried GaP/Si(001)-Interface Studied by Means of Time-Resolved SHG — •Alexander Lerch, Kristina Brixius, Andreas Beyer, Kerstin Volz, Wolfgang Stolz, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität,D-35032 Marburg

Epitaxially grown GaP on Si(001) is a technologically important and structurally well characterized model system for a polar/nonpolar semiconductor interface. We have employed time-resolved optical second-harmonic generation (SHG) to investigate the ultrafast carrier dynamics at the buried GaP/Si interface. The experiments were conducted using 800-nm 45-fs pump and probe pulses in a non-collinear geometry where the SHG response of bulk GaP is suppressed. The samples exhibit characteristic SHG transients on a 5-ps time-scale which are attributed to the build-up of an electric field via charge transfer across the interface. From the linear dependence of the transients on the pump fluence we exclude direct excitation of both GaP and Si bulk with direct band gaps of 2.8 eV and 3.4 eV, respectively. Instead we propose a direct excitation of electronic states at the interface by the 1.55-eV pump pulses which is consistent with a rise-time of the SHG signal faster than 30 fs. We also show, how different SHG components of the interface can be distinguished phase-sensitively by utilizing interference between SHG from GaP bulk and the transients, and discuss the influence of the lattice temperature on the dynamics via electron-phonon scattering.