Electronic properties of wurtzite-phase InP nanowires determined by optical and magneto-optical spectroscopy

Thanks to their peculiar shape and dimensions, semiconductor nanowires (NWs) are emerging asbuilding components of novel devices. The presence of wurtzite (WZ) phase in the lattice structure ofnon-nitride III-V NWs is one of the most surprising findings in these nanostructures: this phase,indeed, cannot be found in the same materials in the bulk form, where the zincblende (ZB) structure isubiquitous, and therefore the WZ properties are poorly known. This review focuses on WZ InP NWs,because growth techniques have reached a high degree of control on the structural properties of thismaterial, and optical studies performed on high-quality samples have allowed determining the mostuseful electronic properties, which are reviewed here. After an introduction summarizing the reasonsfor the interest in WZ InP nanowires (Sec.I), we give an overview on growth process and structuraland optical properties of WZ InP NWs (Sec.II). In Sec.III, a complete picture of the energy and sym-metry of the lowest-energy conduction and valence bands, as assessed by polarization-resolved photo-luminescence (PL) and photoluminescence-excitation (PLE) studies is drawn and compared to all theavailable theoretical information. The elastic properties of WZ InP (determined by PL under hydro-static pressure) and the radiative recombination dynamics of spatially direct and indirect (namely,occurring across the WZ/ZB interfaces) transitions are also discussed. SectionIV, focuses on themagneto-optical studies of WZ InP NWs. The diagram of the energy levels of excitons in WZ materi-als—with and without magnetic field—is first provided. Then, all theoretical and experimental infor-mation available about the changes in the transport properties (i.e., carrier effective mass) caused bythe ZB!WZ phase variation are reviewed. Different NW/magnetic field geometrical configurations,sensitive to polarization selection rules, highlight anisotropies in the diamagnetic shifts, Zeeman split-ting, and field-induced circular dichroism of the emitted light. These characteristics are indeed inherentto the NW crystal symmetry. Such an exhaustive summary of the electronic properties of WZ InPNWs (energy, symmetry, thermal-, and pressure-induced shift of near band gap electronic bands,impurities binding energy, WZ and ZB band-offset values, exciton lifetime, exciton, electron, and holeeffective masses) is valuable in the prediction of fundamental device parameters or as a reference fordetailed band-structure calculations, as summarized in the last section (Sec.V), where also the openissues are critically discussed.Published by AIP Publishing.