Study Of The Interfacial Coupling Between Hexagonal Zinc Oxide And Cubic Oxides

ZnO based semiconductor performs as one of the most potential materials,and improving the crystal quality and doping are still the hot research topics that have attracted research attentions.With the doping of Mg atoms,the band gap of ZnO can be continuously adjustable,which promotes the application of ZnO based materials in ultraviolet(UV)and deep UV electrical devices.Besides,co-doping with multi elemenets has become one of the hot research directions recently.With the request of improving the devices properties and reducing the sizes,coupling at the interface of two materials appears to be the critical issue for investigation.In this work,wurtzite ZnO,MgZnO and N doped MgZnO films were deposited on the substrate of cubic MgO.With the representions of wurzite ZnO and cubic NiO,the kinematic coupling and electronic structures between wurzite oxide and cubic oxide were investigated by in situ synchrotron radiation photoelectron spectra and X-ray absorption spectra as well as ex situ synchrotron radiation X-ray diffraction,and scanning transmission electron microscopy.We have obtained the following results:1."ridge-like" and "particle-like" surface morphologies are observed for the ZnO films grown by tuning the oxygen pressures and activity during the growth processes.From room-temperature photoluminescence(PL)measurements,a strong defect-related green luminescence band appears for the ZnO film with a "particle-like"morphology but was hardly observed in the films with flat "ridge-like" surface morphologies.Our work suggests that the ZnO crystallinity can be improved and defect luminescence can be reduced by designing interfacial layers between substrates and epilayers.2.The optical property of ZnO films grown by MBE was improved by supercritical fluid treatment.Nanostructures generated on the surface of MBE-grown ZnO films using the W-SCCO2 technology without any other catalyst.The self-cataly growth of nanostructures is related to the chemical atmosphere at the interface,and two growth modes were proposed to explain the transformation of ZnO morphologies.The W-SCCO2 was also found to promote the inhibition of the oxygen vacancy defect luminescence by introducing-OH groups onto the films.3.MgZnO films with various Mg contents were prepared on the substrate of MgO(111).The crystal structures of MgZnO films transform from wurtzite to cubic and the crystallinity of the films decreased as the increase of Mg content in the film.The doping of N increase the Mg content in MgZnO film,and on the contrary,the increase of Mg content in MgZnO film promotes the solubility of N atoms.4.A series of NiO films with different thickness were epitaxially grown on the hexagonal substrates of wurtzite ZnO(0001)by molecular beam epitaxy and pulse laser deposition.The ex-situ synchrotron-based XRD and STEM show the highly(100)-oriented texture featuring three domains with a rotation angle of 30�,and the epitaxial relationship at the interface:(110)NiO-? ||(10-10)ZnO,(-1110)NiO-?||(-12-10)ZnO,[001]NiO-?||[0001]ZnO(110)NiO-? ||(0-110)ZnO,(-110)NiO-?||(2-1-10)ZnO?[001]NiO-?||[0001]ZnO(110)NiO-?||(-1100)ZnO,(-110)NiO-?||(-1-120)ZnO,[001]NiO-?||[0001]ZnO The mismathc between wurzite ZnO and cubic NiO was relaxed by forming "T" dislocation at the interface.In-situ synchrotron radiation photoelectron spectroscopy was used to investigate the core level and valence band electronic structures at the interface between NiO film and ZnO substrate,crystal field effect appears at the interface because of the breaking of octahedral symmetry in NiO.The increase of valence state in Ni atom suggests the charge transfer between NiO and ZnO with electrons transfer from NiO to ZnO.By analysing the spectra of synchrotron-based XAS and EELS,there exhibits an increase of 3d unoccupied states in the z plane compared to those in the xy plane as closer to the interface,which proves the charge transfer at the interface.A type-? band alignment with a VBO of 1.4�0.2 eV and a CBO of 1.73�0.2 eV is determined by synchrotron-based ultraviolet photoelectron spectra.The band alignment indicates that the NiO/ZnO structure is capable of electron confinement,an important aspect for the design and application of ZnO-based devices.