Second-harmonic generation imaging for crystal structure characterization in III-V nanowires

Summary form only given. Semiconductor III-V nanowires are one of the key nanostructures for new generation of optoelectronic and nanophotonic devices. The most unique feature of the III-V nanowires is the possibility to engineer crystal phases that cannot be obtained at normal conditions in bulk III-V materials [1]. For example, it is possible to grow III-V nanowires with pure wurtzite, with combined wurtzite/zinc blende phases and with rotational zinc blende twins along single nanowire. The possibilities to engineer crystal structures of III-V materials make nanowires promising structures for nonlinear photonics application. The most common technique to characterize the crystal structure of nanowires is transmission electron microscopy (TEM), but this technique requires to deposit nanostructures on the special TEM substrates and it cannot be used for a non-destructive analysis of nanowires implemented, for example in lab-on-chip devices or computer components.In our work, we present an optical non-destructive method of nanowires crystal structure characterization, based on polarization-dependent second-harmonic generation (SHG) imaging with per-pixel resolution [2]. This method was applied to resolve the areas with zinc blende, wurtzite and rotational zinc blende twins crystal structures along GaAs nanowires [2]. The TEM image of GaAs nanowire and corresponding SHG intensity images are presented in Fig. 1a and 1b. The polarization-dependent SHG intensity images were recorded at different polarizations from 0° to 360°. The Fig.1b demonstrates the example of normalized SHG images at different polarizations of incoming excitation ⃗(). Per-pixel analysis of the recorded polar SHG responses allows to distinguish areas with different crystal structure along single GaAs nanowires. The variations of polar SHG responses shapes (Fig. 1c and 1e) allow precisely resolve zones with wurtzite and zinc blende crystal structures along a nanowire.