Time-resolved Characterization of Non-equilibrium Carrier Dynamics in Gallium Based III-V Materials and Devices

Ga-based III-V materials, such as, GaAs, GaN and AlGaN, have a wide-range of applications in the fields of high-speed, high-temperature, high-power and high-frequency electronic and optoelectronic devices, due to their unique physical properties. This thesis is devoted to the time-resolved characterization of ultrafast, nonequilibrium carrier and phonon dynamics in Ga-based III-V materials and their devices. I present my studies of coherent acoustic phonons (CAPs) and nonlinear optical (NLO) process in GaN and AlGaN single crystals, as well as the ultrafast characterization of epitaxially-grown GaAs meso-structured photodetectors (PDs) and self-switching diodes (SSDs) operating as novel THz emitters and photon sensors. Studies of CAPs and NLO properties in III-Nitrides were accomplished using a femtosecond time-resolved pump-probe spectroscopy. We have experimentally investigated the generation, propagation and detection mechanisms of CAPs and, with the two-side CAPs detection scheme, the intrinsic phonon lifetime was measured to be 80 ns in GaN single crystals at room temperature. The NLO properties of AlGaN single crystals were studied by means of a multi-photon absorption (MPA) technique. My research shows that AlGaN exhibits a large nonlinear correlation factor, with a strong, 310-fs-wide correlation peak. Furthermore, our analysis of the correlation peak amplitude on the pump wavelength allowed us to demonstrate that its spectral dependence agreed very well with the Sheik-Bahae and Hutchings theory for the two-photon absorption (TPA)