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Femtosecond optical pump–probe spectroscopy is employed to elucidate the ultrafast carrier nonradiative relaxation dynamics of bare GaAs and a core–shell GaAs/AlGaAs semiconductor nanowire array. Different from the single nanowire conventionally used for the study of ultrafast dynamics, a simple spin coating and peeling off method was performed to prepare transparent organic films containing a vertical oriented nanowire array for transient absorption measurement. The transient experiment provides the direct observation of carrier thermalization, carrier cooling, thermal dissipation and band-gap energy evolutions along with the carrier relaxations. Carrier thermalization occurs within sub-0.5 ps and proceeds almost independently on the AlGaAs-coating, while the time constants of carrier cooling and thermal dissipation are increased by an order of magnitude due to the AlGaAs-coating effect. The concomitant band-gap evolutions in GaAs and GaAs/AlGaAs include an initial rapid red-shift in thermalization period, followed by a slow blue and/or red shift in carrier cooling, and then by an even slower blue shift in thermal dissipation. The evolution is explained by the competition of band-gap renormalization, plasma screening and band-filling. These findings are significant for understanding the basic physics of carrier scattering, and also for the development of flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]

GaAsSb-Based QW structure nanowires play an important role in the field of nano-optoelectronics. In this manuscript, we report the epitaxial growth of GaAs/GaAs0.75Sb0.25/GaAs single quantum well (SQW) nanowires on a Si (111) substrate by solid source molecular beam epitaxy (SS-MBE) and study the morphology, structure and optical properties of the nanowires. Two morphologies of SQW nanowires are observed, essentially caused by Ga droplets at the top of a small number of nanowires which were not completely consumed. The structure of GaAs/GaAsSb/GaAs SQW nanowires was characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDXS). The results show that the nanowires have a zinc blende crystal structure. The photoluminescence (PL) spectrum of GaAs/GaAs0.75Sb0.25/GaAs SQW nanowires shows a peak emission wavelength of ∼1.2 μm at room temperature. Finally, the controllable growth of nanowires was explored by changing the Ga interruption time. This work would have a positive influence on the development of optoelectronic devices based on GaAs/GaAsSb/GaAs quantum well nanowires. [ABSTRACT FROM AUTHOR]