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

Abstract

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.

Kinetics-Driven Crystal Facets Evolution at the Tip of Nanowires: A New Implementation of the Ostwald-Lussac Law

“…Controlled growth of crystals is crucial to designing and obtaining the extraordinary physical, chemical, electronic, and mechanical properties of nanomaterials. − Among many endeavors toward controlled synthesis of nanostructures, manipulating the crystal facets has been one of the most intensively studied aspects in materials science. Because of the distinguishing chemical activity on different facets, the exposed crystal facets are always the dominating factor that determines the materials’ geometry, catalytic activity, structural stability, and toxicity. − In principle, a stable crystal system tends to expose the facets with the lowest surface energy. For example, metal nanoparticles with a face-centered cubic lattice, such as Au and Pt, typically exhibit a truncated-octahedron shape exposing their {111} and {100} facets. , Rutile TiO 2 , a common paint and catalytic material, typically shows a rectangular geometry covered by the {001} and {110} facets .…”

Exploring Au Droplet Motion in Nanowire Growth: A Simple Route toward Asymmetric GaP Morphologies

“…50−53 Wurtzite III−V nanowires grown in the ⟨0001⟩ direction usually exhibit low surface energy {101̅ 0} or {112̅ 0} planes as sidewalls, which results in a regular hexagonal cross-section. 54,55 TEM images (Figure 3D) of our asymmetric GaP nanowires present an irregularly shaped cross section, which can be interpreted as two juxtaposed hexagons with intermediary facets between them. The main facets correspond to {112̅ 0} family planes, according to the SAED pattern indexed in the [0001] zone axis (inset, Figure 3D); however, the overall morphology shows a quasi 2-fold symmetry.…”

“…The overall morphology of metal-catalyzed nanowires is determined by the balance of axial VLS and the VS growth on the exposed sidewalls. When nanowires expose facets with different polarities and hence distinct VS growth rates, the overall morphology can be quite distinct from the metal-catalyzed nanowire core. − Wurtzite III–V nanowires grown in the ⟨0001⟩ direction usually exhibit low surface energy {101̅0} or {112̅0} planes as sidewalls, which results in a regular hexagonal cross-section. , TEM images (Figure D) of our asymmetric GaP nanowires present an irregularly shaped cross section, which can be interpreted as two juxtaposed hexagons with intermediary facets between them. The main facets correspond to {112̅0} family planes, according to the SAED pattern indexed in the [0001] zone axis (inset, Figure D); however, the overall morphology shows a quasi 2-fold symmetry.…”

GaAs Nanowires Grown by Catalyst Epitaxy for High Performance Photovoltaics

“…Most NWs are synthesized epitaxially on a single crystalline GaAs wafer via VLS or VSS growth mechanisms by molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) techniques [90][91][92]. Apart from the absence of expensive epitaxial substrates, catalyst epitaxy by metal nanoparticles (NP, such as Au, Ni, Ag, and Pd for GaAs NW) has been verified a cost-effective and versatile manipulating strategy for synthesizing NWs on amorphous SiO 2 or glass substrates [93,94].…”