Crystal Phase and Facet Effects on the Structural Stability and Electronic Properties of GaP Nanowires

The control of electronic properties of GaP nanowires is of particular importance for their applications in nanoelectronics and optoelectronics. However, a fundamental understanding is still lacking of atomic and electronic properties of GaP nanowires due to the diversity of the crystal phase in the fabricated nanowires. Here we reveal the crucial role of the crystal phase and nanowire facets in the structural and electronic properties of zinc-blende, wurtzite, and polytypic GaP nanowires by using the first-principles calculations. The stability mechanism of GaP nanowires depends on the competition between the crystal phase and facet effects: the former dominates the stability of larger-sized nanowires, but the stability of ultrathin nanowires is mainly determined by the latter. This mechanism can be applied to explain a large amount of experimental observations about the formation of stacking faults and twin defects during the growth of III-V semiconductor nanowires. Likewise, electronic properties of GaP nanowires, including band gap values and the band structure characteristic, are sensitive to not only the nanowire size but also the crystal phase. Moreover, the quantitative relationship between the band gap of GaP nanowire polytypes and their diameter has been established, and the calculated band gaps agree well with the experimental data. Our results can provide a theoretical guidance for engineering electronic structures of GaP nanowires as well as their applications in optoelectronic devices.