Investigation On The Preparation And Optical Properties Of MgZnO Alloy And MgZnO/ZnO Heterostructure

Recently, ZnO-based semiconductors have been attracting increasing attention as promising candidates for optoelectronic applications in ultraviolet (UV) regions. It becomes one of the researches hotspot in the optoelectronic region. In order to obtain the high-performance light-emitting diodes (LED) devices and decrease the threshold of stimulated emission, one of the key techniques is to construct a heterojunction to realize double confinement actions for electrons and photons in optoelectronic devices. Because the ionic radius of Mg²⁺(0.57A) is close to that of Zn²⁺(0.6 (?)), Mg_xZn_1-xO alloy is considered to be a suitable potential barrier material by doping Mg substitute for Zn²⁺ ion in ZnO. Hence, it is necessary to study the structure and characteristic of Mg_xZn_1-xO alloy films and MgZnO/ZnO heterostructures.In this thesis, we investigate the structural and optical properties of MgZnO alloy thin films and MgZnO/ZnO heterostructures prepared by the plasma-assisted molecular beam epitaxy (P-MBE). And the superradiation processes of MgZnO/ZnO single well quantum (SQW) are also studied. The details are as follows:1. Mg_xZn_1-xO alloy thin films were prepared on c-plane sapphire substrates by P-MBE. In the range of x≤0.28, Mg_xZn_1-xO alloy thin films with wurtzite structure were obtained. In the range of 0≤x≤0.65, Mg_xZn_1-xO alloy thin films have completed the transition from wurtzite structure to cubic structure. Effects of phase transition of Mg_xZn_1-xO (0≤x≤0.65) on absorption, photoluminescence and resonant Raman spectra were researched at room temperature (RT).2. Optical properties of Mg_xZn_1-xO (0≤x≤0.20) alloy thin films fabricated on c-plane Al₂O₃ substrates by P-MBE were studied. Reflection high-energy electron diffraction (RHEED) and X-ray double crystal diffraction analyses indicate that the samples are single-crystal films with a hexagonal wurtzite structure. Photoluminescence spectra of Mg_xZn_1-xO alloy thin films show an intense ultraviolet (UV) emission at RT.The origin of this UV emission was attributed to the free exciton emission at RT.3. ZnO /Mg_0.12Zn_0.88O single quantum well (SQW) with different well width were grown by P-MBE. With decreasing of the ZnO layer thickness, the emission band from ZnO layer show a distinct blue-shift due to quantum confinement effect. We observed a process of the carrier injection from Mg_0.12Zn_0.88O capping layer to ZnO layer which attributed to the existent of interface potential barrier. And the carrier injection process becomes weak with decreasing the well width due to the interface improvement.4. The exciton characteristic of ZnO /Mg_0.12Zn_0.88O single quantum well (SQW) with 1.5 nm ZnO well width was investigated. Under the high excitation density, the superradiation process at room temperature is attributed to P-band emission due to exciton-exciton collision.Keywords: plasma-assisted molecular beam epitaxy; MgZnO/ZnO heterostructures; Mg_xZn_1-XO alloy; Superradiation; Photoluminescence...