Local Electronic Structures and Polarity of ZnO Nanorods Grown on GaN Substrates

Abstract

The polarization and surface reactivity of the ZnO nanorods (NRs) grown on the (0001̅) N-polar GaN substrate and the (0001) Ga-polar GaN substrate by hydrothermal process were studied. We found that the polarization direction of the ZnO NRs grown on the GaN substrates depends on the surface polarity of the GaN growth substrates. The surface planes of ZnO NRs on the Ga-polar GaN substrate and the N-polar GaN substrate are the Zn-polar (positive-charged surface) and the O-polar (negative-charged surface) ZnO surface plane, respectively. The O-polar ZnO plane is more chemically stable than the Zn-polar ZnO plane. After the water dissolution process, the Zn-polar ZnO NRs transformed to the tube-like nanostructure and the O-polar ZnO NRs formed hexagonal facets on the top of ZnO NRs. X-ray absorption spectroscopy (XAS) was used to analyze the electronic structures of the growth surface of the ZnO NRs on the two GaN growth substrates. The absorption peaks in the XAS spectral reveal the density of the dangling bonds on the terminal surface of ZnO NRs and the occupancy probability of the hybridized orbitals of the terminal surface of ZnO NRs. With the information on the electronic structure of the surface planes of the ZnO NRs, the surface plane of the ZnO NRs on the different GaN substrates can be verified.

Polarity-Dependent Growth Rates of Selective Area Grown ZnO Nanorods by Chemical Bath Deposition

“…It is worth noticing that polarity is a bulk crystallographic property and differs from surface termination, namely in that the O- and Zn-polar c -planes can both be O- or Zn-terminated. , The polarity in wurtzite semiconducting compounds such as ZnO and GaN has been extensively investigated. − It is known to greatly affect surface stability and configuration, ,,,− ,,,, chemical reactivity, , etching behavior, , growth rate, ,,, morphology, , dopant incorporation, as well as electrical and optical properties. , These polarity-dependent properties have so far been almost exclusively determined in the case of ZnO single crystals and epitaxial films. They are still open to a very large extent in the case of ZnO nanostructures including NRs.…”

“…Overall, the issue of polarity in the field of ZnO nanostructures have been reported depending on the polarity of the ZnO nucleation surface ,,,,− and investigated regarding their polarity itself. The physical and chemical vapor deposition techniques typically results in the formation of Zn-polar ZnO NRs ,,,− or nanostructures following the catalyst-free or self-induced approaches, , regardless of the polarity of the nucleation surface.…”

ZnO Nanocrystals as Anode Electrodes for Lithium-Ion Batteries

“…ZnO has superior advantages such as low cost, facile preparation, morphologic diversity, and high chemical stability. ZnO nanocrystals with different morphologies have some special properties of physics, so intense interests have been devoted to the synthesis of ZnO with various morphologies such as nanowires [10], nanobelts [11], nanorods [12], and nanosheets [13].…”

Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

“…It indicates that when the epi-layers have the same polarity as the substrates do, the interfaces are relatively stable. Both interfaces were also speculated by experimental groups [92]. However, they may not be energetically favorable in all cases, because these interfaces can be negatively or positively charged.…”

“…Next, we considered different interfacial configurations. Experimentally, it is observed that the epitaxial crystal has the same polarity as the substrate without interface modifications and substrate pre-treatment [26,28,92]. Therefore, we first tried all the interface configurations without adlayers.…”