Time-Resolved Surface Photoelectron Spectroscopy of Photoexcited Electron and Hole Dynamics on GaAs Using 92 eV Laser Harmonic Source

We have developed a time-resolved surface photoelectron spectroscopy system based on a 1.5 eV laser-pump and 92 eV high-order harmonic probe configuration that enables us to measure the electron and hole dynamics on a semiconductor surface. Core-level photoelectron spectra of GaAs(001) were successfully obtained with a single 59th harmonic, which was selected by using a pair of Mo/Si multilayer mirrors with a narrow reflection bandwidth. We observed transient energy shifts of the Ga 3d core level photoelectron peak of approximately 200 meV towards a higher binding energy, indicating that the surface potential changed due to the spatial separation of electron--hole pairs generated by the laser irradiation. The relatively slow recovery of the Ga 3d core level shift with a time constant of a few ns is dominated by the recombination process of the excess surface charges generated by the laser irradiation.