Ultrafast carrier dynamics in single ZnO nanowire and nanoribbon lasers

Time-resolved second-harmonic generation (TRSHG) and transient photoluminescence (PL) spectroscopy are utilized to probe the ultrafast creation and subsequent relaxation of excited carriers immediately following band-gap excitation in single ZnO nanowire and nanoribbon lasers. The TRSHG signal consists of a 1-5 ps recovery present only during strong lasing and a 10-80 ps intensity-dependent component. The transient PL response from single structures exhibits an 80 ps decay component independent of pump power (free exciton PL), and a < 10 ps power-dependent component (stimulated emission) that shifts to earlier delay by ca. 10 ps at high pump fluence.