It is common practice to employ the band structure parameters of bulk materials (e.g., gap energy, effective mass and gyromagnetic factor of carriers, energy of impurity levels) for estimating the electronic properties of quantum heterostructures and nanostructures. However, this approach breaks down in many types of III-V (notably, GaAs and InP) nanowires (NWs), which may grow in the wurtzite (WZ) phase, a crystal structure not existing in the bulk. In fact, even the basic spin and transport properties are unknown in most WZ NWs, thus limiting the design of heterostructured WZ NWs as well as of 1D WZ/zincblende homostructures, in which the crystal phase varies purposely along the NW growth axis while keeping the NW composition uniform and strain negligible. Here, we report on magneto-photoluminescence (up to B=30 T) results of WZ InP NWs grown by selective-area epitaxy that provides pure-phase, perfectly ordered NWs. The analysis of the diamagnetism and Zeeman splitting of exciton and acceptor impurity states as a function of temperature, field orientation, and circular polarization permits to disentangle the dynamics of oppositely charged carriers from the Coulomb interaction, and, thus, to determine the value and anisotropy of mass1 and gyromagnetic factor2 of electrons and holes separately. A theoretical model2,3 based on a 8x8 k⋅p Hamiltonian, including spin-orbit coupling terms, has been develop providing very good agreement with the experimental data. Interestingly, the degree of mass anisotropy found for WZ InP NWs is remarkably similar to that found in other WZ bulk materials (GaN, InN and ZnO). Furthermore, for B parallel to the NW axis and >12 T, the Zeeman splitting is non-linear2,3. This finding is theoretically explained by a field-dependent hole gyromagnetic factor gh(B) due to the mixing between Landau levels originating from the A, B and C valence bands of the WZ lattice. This is a general feature of WZ materials observed also in InGaAs4 and GaAs5 WZ NWs. To conclude, our results highlight peculiar features of WZ NWs and offer pertinent inputs for engineering the electronic properties of NW quantum heterostructures and crystal-phase homostructures.
1 D. Tedeschi et al, Nano Lett. 16 (2016) 6213.
2 D. Tedeschi et al, unpublished.
3 P.E. Faria Junior et al, Phys. Rev. B 93 (2016) 235204; P.E. Faria Junior et al, unpublished.
4 M. De Luca et al, ACS Nano 7 (2013) 10717.
5 M. De Luca et al, unpublished.