The role of polarity in nonplanar semiconductor nanostructures

The lack of mirror symmetry in binary semiconductor compounds turns them into polar materials, where two opposite orientations of the same crystallographic direction are possible. Interestingly, their physical properties (e.g., electronic or photonic) and morphological features (e.g., shape, growth direction, and so forth) also strongly depend on the polarity. It has been observed that nanoscale materials tend to grow with a specific polarity, which can eventually be reversed for very specific growth conditions. In addition, polar-directed growth affects the defect density and topology and might induce eventually the formation of undesirable polarity inversion domains in the nanostructure, which in turn will affect the photonic and electronic final device performance. Here, we present a review on the polarity-driven growth mechanism at the nanoscale, combining our latest investigation with an overview of the available literature highlighting suitable future possibilities of polarity engineering of semiconductor nanostructures. The present study has been extended over a wide range of semiconductor compounds, covering the most commonly synthesized III–V (GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb) and II–VI (ZnO, ZnTe, CdS, CdSe, CdTe) nanowires and other free-standing nanostructures (tripods, tetrapods, belts, and membranes). This systematic study allowed us to explore the parameters that may induce polarity-dependent and polarity-driven growth mechanisms, as well as the polarity-related consequences on the physical properties of the nanostructures.
ICN2 acknowledges funding from Generalitat de Catalunya 2017 SGR 327 and the Spanish MINECO coordinated project ENE2017-85087-C3. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science Ph.D. program. S.M.S. acknowledges funding from “Programa Internacional de Becas “la Caixa”-Severo Ochoa”. The HAADF-STEM experiments were conducted in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragon-Universidad de Zaragoza. A.F.i.M. thanks SNSF for funding through the NCCR QSIT. This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 654360 NFFA-Europe. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 823717 – ESTEEM3.
We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).