Tuning the Surface Morphologies and Properties of ZnO Films by the Design of Interfacial Layer

Abstract

Wurtzite ZnO films were grown on MgO(111) substrates by plasma-assisted molecular beam epitaxy (MBE). Different initial growth conditions were designed to monitor the film quality. All the grown ZnO films show highly (0001)-oriented textures without in-plane rotation, as illustrated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). As demonstrated by atomic force microscopy (AFM) images, “ridge-like” and “particle-like” surface morphologies are observed for the ZnO films grown in a molecular O2 atmosphere with and without an initial deposition of Zn adatoms, respectively, before ZnO growth with oxygen plasma. This artificially designed interfacial layer deeply influences the final surface morphology and optical properties of the ZnO film. 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.Electronic supplementary materialThe online version of this article (10.1186/s11671-017-2301-8) contains supplementary material, which is available to authorized users.

Epitaxial growth of Zn‐rich (Mg,Zn)O thin films on MgO substrates with different surface orientations

“…Once nucleated, the domain gradually reaches the top surface. The surface energy of the inclined (Mg,Zn)O thin film is between those along the c‐ and m‐planes, which is consistent with the AFM results 32,33 …”

“…The surface energy of the inclined (Mg,Zn)O thin film is between those along the c-and m-planes, which is consistent with the AFM results. 32,33 The electronic structures of the (Mg,Zn)O films were investigated by synchrotron-based XAS. The incident angle was perpendicular to the sample.…”

Development of in situ characterization techniques in molecular beam epitaxy

“…The presence of bright specular stripes at 1.5 × indicates a flat and phase-pure CaTi 5 O 11 surface, while the TiO 2 -B membrane also exhibits distinct and unadulterated 1.5 × stripes. Additionally, recording and analyzing RHEED diffraction patterns enables the optimization of growth conditions of different materials and the realization of high-quality epitaxy [67,72] . As shown in Fig.…”

Structural, Morphological, Optical, Luminescent and Magnetic Properties of Nanostructured ZnO Thin Film

“…As seen from the spectra, ZnO thin film consists of five luminescence peaks at wavelength 360, 390, 411, 494 and 520 nm. The strong peak at 359 nm is due to free exciton (FE) [50] and the 390 nm peak (3.17 eV) corresponds to excitonic emission from near band edge transition of wide band gap of ZnO, i.e, the recombination of excitons through excitonexciton collision process [51]. The strong band edge transition found to be red shifted compared to the bulk ZnO.…”