Preparation And Properties Of Quaternary MgxZn_1-xO_1-yS_y Alloy Thin Films Grown By PLD

There are two hot research fields of ZnO, those are the energy bandgap engineering and p-type doping of ZnO. Taking advantage of ZnMeO (Me=Mg, Be, etc.) alloy to regulate the band gap of ZnO has been widely studied. Meanwhile, the research of anionic alloyed ZnOX (X=S, Se, etc.) is also arisen. However, the real cationic and anionic codoped ZnMeOX quaternary alloy has not been reported at home and abroad. This thesis presents to form an MgZnOS quaternary alloy through equivalent anonic (S) and cationic (Mg) ion codoping in ZnO, in order to freely modulate the band gap structure and regulate the band gap in a more wide range. At the same time, through the ionic compound modificate action of cation and anion to regulate the electronic band structure of ZnO alloy, so that it is beneficial to p-type doping. This work aims to provide a new idea and data for the band gap engineering research and p-type doping of ZnO. In this thesis, we use homemade MgxZn1-xO1-ySy ceramic as the target material, O2as the reaction gas to deposit film samples with the pulsed laser deposition (PLD) method. The c-plane orientation MgxZn1-xO1-ySy films were prepared on the c-plane sapphire substrate. We systematically studied the influence of substrate temperature and oxygen partial pressure on MgxZn1-xO1-ySy structure and performance, the influence in film performance as Mg and S composition changed were discussed. The main research contents and results are as follows:Firstly, the oxygen partial pressure was fixed at3Pa. High-quality of films with sigle phase were succeccfully prepared through systematically study the substrate temperature. The results showed that c-plane orientated MgxZn1-xO1-ySy films with the best crystalline quality were obtained at a substrate temperature of700℃, and the optical transmittance of the films in the wavelength range of visible light are above80%.Secondly, with the fixed substrate temperature of700℃, the influence of growth O2 pressure on MgxZn1-xO1-ySy film surface morphology, crystal structure, composition, and the optical properties was studied systematically. By changing oxygen pressure, we got a series of single-phase MgxZn1-xO1-ySy films with different sulfur contents. Keeping Mg content in the films at about10%, alloyed thin films present a single wurtzite structure during the whole sulfur content changing range of14%-89%except for the sulfur content is48%. The thin film band gap is the smallest2.78eV especially when the S content is about38%(oxygen pressure for3Pa).Finally, we used targets of different Mg contents to deposite films at the same temperature and oxygen pressure. We got a series of single phase MgxZn1-xO1-ySy films with sulfur content at around80%, but the content of Mg is in the range of7-21%. The results showed that the films’c axis lattice constant decreased slightly with the increase of Mg content. At the same time, the band gap of MgxZn1-O1-ySy quaternary alloy is smaller compared to the corresponding ternary MgxZn1-xO alloy films with same Mg content, but larger than the corresponding ternary ZnO1-ySy alloy films with same S content, and with increasing Mg content, the band gap broaden effect is stronger. For MgxZn1-xO1-ySy films with same Mg content (around10%) and different S content (14%-89%), the c axis lattice constant increased obviously with the increase of S content. Similarly, the band gap of MgxZn1-xO1-ySy quaternary alloy is smaller compared to the corresponding ternary MgxZn1-xO alloy films with same Mg content, but larger than the corresponding ternary ZnO1-ySy alloy films with same S content, and the relationship of the band gap change with content of S in the MgxZn1-xO1-ySy films is consistent with that of the ZnO1-ySy films with the same S content.These results showed the effect of that the Mg element and S elements be doped into ZnO on the phase structure and optical properties of ZnO. It is contributated to help us understand the mechanism that the effect of Mg and S codoping on the modulation of the electronic structure and band structure of ZnO, and make a foundation on the realization of p-type ZnO through theoretical and experimental method in the future.