ZnO and MgZnO Nanostructures and Heterostructures
- Publication Type:
- Thesis
- Issue Date:
- 2021
Open Access
Copyright Clearance Process
- Recently Added
- In Progress
- Open Access
This item is open access.
ZnO-based heterostructures and nanostructures have attracted significant interest owing to their wide range of technological applications. The recent achievement of high electron mobility at the MgZnO/ZnO heterointerface has sparked great interest in a multitude of research fields. In order to exploit the extraordinary electron states at the MgZnO/ZnO interface, high quality films with bespoke optical and electronic properties must be achieved. Although the ZnO-based heterostructures have been widely explored for various applications, where the performance is often hindered by intrinsic and extrinsic defects. This work aims to elucidate the physics of defects and the properties of ZnO-based thin films, interfaces and 2D nanosheets.
Oxide-based multiple quantum wells (MQWs) were investigated using cathodoluminescence (CL) and high-resolution electron microscopy techniques. A rapid remote plasma annealing (RRPA) method was used to treat MgZnO/ZnO MQWs in order to modify their defect structure. Following the RRPA in hydrogen, the MQW optical emission increased by more than 10 times after a 40 seconds treatment, while the basal stacking faults (BSFs) and point defects emissions were completely quenched. Furthermore, the RRPA-treated MQWs were found to be highly stable up to a temperature of 400°C.
A major challenge in the development of ZnO-based devices is the lack of reliable p-type material. In this work, chemical and optical signatures of nitrogen in N-doped MgZnO were investigated using near-edge X-ray absorption fine structure (NEXAFS) and photoluminescence (PL). The MgZnO epilayer, grown under nitrogen ambient, exhibits higher resistivity compared with epilayers grown under oxygen or vacuum atmospheres, and displays a dominant donor-acceptor-pair (DAP) peak located at 160 meV below its exciton emission. NEXAFS reveals that nitrogen in the N-doped MgZnO exists in multiple chemical states with molecular N2 and substitutional N on O sites (NO) being the dominant species. The PL emission peak at 3.45 eV in the N-doped MgZnO is attributed to a shallow donor to a deep acceptor recombination, where the compensating acceptor is most likely molecular N₂.
The last part of this thesis reports the luminescence and morphological properties of ZnO 2Dnanosheets, fabricated by chemical exfoliation of ZnO microparticles. High-spatial-resolution CL was employed to acquire the optical properties of individual nanosheets. Combined CL and PL analysis shows strong thickness-dependent quantum confinement of excitons in few-atomic-layer thin nanosheets, which leads to substantial variations in the excitonic and phonon coupling properties. The superior excitonic properties of ZnO nanosheets could potentially lead to the development of efficient nano-optoelectronic devices.
Please use this identifier to cite or link to this item: