Studies On ZnO, ZnMgO Films And ZnMgO/ZnO Quantum Well Structures Grown By PLD

ZnO is a direct wide band-gap semiconductor with E_g = 3.37 eV, and has large exciton binding energy of 60 meV, which assures efficient exciton emission even at high temperatures above room temperature. In addition, ZnO has many advantages involving low epitaxial growth temperature, more resistant to radiation damage, and relatively low cost. Owing to these merits, ZnO has attracted considerable attention as a promising material for optoelectronic devices such as UV light-emitting diodes (LEDs), Laser diodes (LDs) and photodetectors. To realize the potential applications of ZnO based optoelectronic devices, it is necessary for the research of band-gap engineering of ZnO. Zn_1-xMg_xO alloy films can tune the band gap from 3.3 eV to 4.5 eV via substituting Mg on the Zn site in the ZnO films, while maintaining the wurtzite structure. Moreover, it is well matched to ZnO lattice. ZnMgO/ZnO heterosystem allows to realize quantum well (QW) structure, which can improve the emission efficiency of devices and modulate the working waveband.In this thesis, based on the introduction of past and current research on ZnO films and ZnO-based devices, we deposited ZnO and Zn_1-xMg_xO thin films on Si (111) substrates, and grew ZnMgO/ZnO quantum well structures with ZnO buffer layer introduced. The main results were obtained as follows:1. We prepared high-quality c-axis oriented ZnO films on Si (111) substrate by pulsed laser deposition (PLD) and systematically analyzed the influence of experimental parameters on the films quality. The optimal growth conditions were obtained.2. We prepared high-quality c-axis oriented wurtzite structure ZnMgO films on Si (111) substrate by pulsed laser deposition (PLD) using a Zn_0.9Mg_0.1O ceramic target. The optimal growth conditions of ZnMgO films were got and we analyzed the relationship between Mg concentration and the ZnMgO films band gap.3. ZnMgO/ZnO/ZnMgO single quantum well structures were fabricated by PLDon Si (111) substrate with 4 nm well width. The room-temperature photoluminescence results from the quantum well structure showed 40 meV blueshift compared with single layer ZnO film, indicating a quantum confinement effect.4. ZnMgO/ZnO multiple quantum well structure also was grown by PLD on Si(111) substrate, which well layer was 3 nm. The room-temperature photoluminescence results from the multiple quantum well structure showed 70 meV blueshift compared with single layer ZnO film, which indicated the quantum confinement effects in the quantum wells can be observed up to room temperature. The TEM image showed that the interfaces of the multiple layer structure were clear and smooth, confirming we successfully prepared ZnMgO/ZnO multiple quantum well structures.