Structural properties of Cu2O epitaxial films grown on c-axis single crystal ZnO by magnetron sputtering

Abstract

Epitaxial Cu2O films grown by reactive and ceramic radio frequency magnetron sputtering on single crystalline ZnO (0001) substrates are investigated. The films are grown on both O- and Zn-polar surface of the ZnO substrates. The Cu2O films exhibit a columnar growth manner apart from a ∼5 nm thick CuO interfacial layer. In comparison to the reactively sputtered Cu2O, the ceramic-sputtered films are less strained and appear to contain nanovoids. Irrespective of polarity, the Cu2O grown by reactive sputtering is observed to have (111)Cu2O||(0001)ZnO epitaxial relationship, but in the case of ceramic sputtering the films are found to show additional (110)Cu2O reflections when grown on O-polar surface. The observed CuO interfacial layer can be detrimental for the performance of Cu2O/ZnO heterojunction solar cells reported in the literature.

Epitaxial Strain-Induced Growth of CuO at Cu2O/ZnO Interfaces

“…23 The XRD of the current specimens showed that the cell parameters of the Cu 2 O films were 0.4318 and 0.4301 nm for the O-and Zn-polar substrates, respectively. 12 This shows that the lattice is only 1.1% and 0.7% strained relative to unstrained Cu 2 O (a = 0.427 nm). The twin growth could be assumed to have relaxed the strain induced by epitaxy.…”

“…The Cu 2 O films investigated in the present study were grown by direct current/radio frequency (dc/rf) reactive magnetron sputtering on c-axis-oriented single-crystal ZnO wafers purchased from Tokyo Denpa Co., Ltd. Detailed description of the deposition parameters is reported by Gan et al 12 In brief, the substrate wafers were double-side polished and pretreated to make sure they were free of any contamination before the sputtering deposition. One side of such a prepared wafer served as the Zn-polar substrate while the other side as the O-polar substrate.…”

Metal Oxide Thin-Film Heterojunctions for Photovoltaic Applications

“…For instance, reducing the defect density at the heterojunction interface to a minimum is important in order to avoid recombination losses. Unfortunately, the small enthalpy of formation for Cu 2 O (~170 kJ/mol) makes the interface prone to oxidation, e.g., a few nm thick intermediate CuO layer was reported to form at the ZnO/Cu 2 O interface [5], which may severely affect the current transport in Cu 2 O-based heterojunction devices since the defect density in this thin interface layer is typically much higher than that of the bulk Cu 2 O layer. Furthermore, the relatively low electron affinity of ~3.2 eV for Cu 2 O makes alignment of the energy bands challenging for ZnO/Cu 2 O heterojunction solar cells.…”

Effects of processing force on performance of nano-resonators produced by magnetron sputtering deposition

“…Depending on the processing conditions, materials can be obtained with specific mechanical, magnetic and optical properties, microstructures, and surface textures. For example, Gan et al [21] investigated the structural properties of Cu2O-epitaxial films, Sun et al [22] determined the optical and electrical performance of thermochromic V2O3 thin films, Cao and Zhou [23,24] determined the magnetic properties of CoZrNb and FeNiCr films, Mirzaee et al [25] examined the surface textures of ZnO films, Rode et al [26] studied effects of deposition rate on surface roughness of Al films, Zenkin et al [27] investigated the thickness dependence of wettability and surface properties of HfO2 thin films, Han et al [28] explored the composition and structure of TiHxHe films, Gudla et al [29] investigated the microstructure evolution of AlZr and AlZrSi coatings during heat treatment processes, Kobata and Miura [30] examined the mechanical and thermal properties of TiCuZrNiHfSi thin films, Pshyk et al [31] analyzed the structural, morphological and tribo-mechanical properties of AlNTiB2TiSi2 coatings, and Mazur et al [32] investigated structural, optical, and micro-mechanical properties of (NdyTi1−y)Ox thin films produced by magnetron sputtering. Moreover, effects of the magnetron sputtering processing on the surface roughness of ultra-thin films are investigated in different studies [33][34][35][36][37].…”