Ultrafast dynamics in semiconductor devices

This research focuses on three types of GaAs-based semiconductor devices, namely oxide confined vertical-cavity surface-emitting lasers (VCSEL), GaAs/AlGaAs quantum dots and GaAs microdisk lasers. An individual transverse mode distribution in a VCSEL has been resolved by a scanning confocal microscope in connection with an optical spectrum analyzer. With resonant femtosecond pulse injection, we directly perturb the cavity field of a VCSEL. After the injection, the lasing and nonlasing mode dynamics are measured. Spatio-temporal resolution of the VCSEL's modes helps us to understand how to lock transverse modes and work toward a new type of mode-locked pulse laser. By injecting cross-polarized laser pulses into a VCSEL cavity, we also studied the ultrafast polarization effects of a single-mode VCSEL. Based on time-resolved microscopic photoluminescence (μPL) from single self-assembled GaAs/AlGaAs quantum dots, we unambiguously identify one of the emission lines as arising from positive trions (two holes and one electron) in these nominally undoped quantum dots. The trion is formed via tunneling of one electron out of the dot after optical excitation of a biexciton. The rise time of the trion emission line matches the decay time of the biexciton due to electron tunneling. Time-resolved whispering-gallery modes (WGMs) of GaAs microdisk lasers show a redshift in time. After the fs laser pulse pump, there is a turn-on delay of the microdisk laser lasing emission. With the increasing pump power, the WGMs shift to shorter wavelength