Linear and Nonlinear Optical Properties of Single GaAs Nanowires with Polytypism

We report the linear and nonlinear optical properties of single GaAs nanowires with polytypism effect. Electron transmission microscopy experiments show that the nanowires contain wurtzite segments as well as zinc blende segments with two different crystallographic orientations. Time-resolved photoluminescence spectroscopy of single nanowires shows ultrafast radiative recombination lifetimes in the range of 20-70 ps as a consequence of the charge scattering in the type-II band alignment between WZ and ZB segments and or by the high surface area of the nanowires. Polarization resolved second harmonic generation in the nanowires found to be highly sensitive to the crystallography of the nanowires. All three crystal axes orientations of the nanowires were determined. Furthermore, the volume fraction of the ZB segments oriented in the [0-11] and in the [01-1] directions was precisely determined for the first time by optical measurement besides the TEM technique.