Technological Investigation On ZnO-Based Ultraviolet Photoelectric Thin Films And Devices

Zinc oxide (ZnO) is a wide bandgap semiconductor material, the bandgap is 3.37eV at room temperature. The crystal structure and physical properties of ZnO are similar to GaN material which is one of the third generation semiconductor materials. Furthermore, ZnO material has stable chemical properties and strong restitance to high temperties as other oxide material. The resource for fabricate ZnO material is wide, the fabricaiton cost is low and the process is sample. Thus, ZnO material has potential application in ultraviolet emitting and detector devices, and become the research focus after GaN material.In order to fabricate high performance ZnO-base optoeletric device, the fabrication of high qualtity ZnO thin film is most important. At present, high quality ZnO thin film is often grow on sapphire and GaN substrates. These substrates are costly,hard to cleave and incompatible to the integrated microelectronic and optoelectronic fabrication processes.In this thesis, ZnO thin films were grown on Si main substrate and quartz aided substrates using radio-frequency reactive magnetron sputtering method.In this method, metal Zn was used as the sputtering target, the argon and oxygen gases were used as the sputtering gas and reactive gas, respectively. The influences of the sputtering voltage and O/Ar ratio on the structure, luminescence, tramistance, optical bandgap, electricy, thickness, Zn/O ratio of ZnO thin film were mainly investigated. The optimized technological parameters for fabricating ZnO thin film were provied.In order to improve the quality of ZnO thin film grown on Si substrate and solve the problems of the lattice mismatch and stress between Si substrate and ZnO thin film, two improving methods were put forward. One method is to grow a thin layer of aluminum oxide buffer latyer on Si substtate firstly. This aluminum oxide buffer layer was grown by reactive magnetron sputtering methon, and metal Al was used as the sputtering target. The structure, Al/O ratio and morphology of the aluminum oxide buffer laye and also discussed; then the ZnO main layer were grown on aluminum oxide buffer laye also by reactive magnetron sputtering method in the same sputtering vacuum chamber, the influences of the thickness of aluminum oxide buffer layer on the structure and optical properties of ZnO main layer were mainly investigated. It was found that the structure and optical quality of ZnO thin films were improved by introducing aluminum oxide buffer layer and the optimized thickness of aluminum oxide buffer layer was given. The other method to improve the quality of ZnO thin film proved by us firstly in China is to introduce the photolithography techonology in the fabrication process. In this method, lots of "step" were made in the Si substrate by photolithography and etching processes to release stress caused by the lattice mismatch between Si substrate and ZnO thin film and provide more "initial nucleation site" for the subsequent growth of ZnO thin film, then ZnO thin films were grown. Lastly, the influenc of two kinds of "step" shape on the quality of ZnO thin film were studied, it was found that the full-width at half the maxmium of (002) diffration peak for ZnO thin film decreased and the ultraviolet emission intensity increase obviously, thus the quality of ZnO thin films were improved.After successfully fabricated ZnO thin film, the ZnO-based photoconductive and pn junction ultraviolet detectors were investigated in this thesis. The structure of ZnO photoconductive detector was Al/ZnO/Al. This detector’s responsivity was higher in the ultraviolet region, the maximum resonsivity was at 362nm. Due to the fact that ZnO mostly shows n-type conductive and difficult to realize p-type conductive, heterojunction strucuture of ZnO-based pn junction ultraviolets were studied. P-Si/n-ZnO heterojunction detector had responsivity in both visible and ultraviolet region. In order to eliminate the resonsivity in visible region for the detector and realize a single responsivity in the ultraviolet region, the growth of NiO (a p-type wide-bandgap transparent semiconductor material) thin film were firstly studied in China by us using radio-frequency magnetron sputtering method; by adjusting the sputter voltage and O/Ar ratio, the quality of NiO thin films were improved. On the basis of successful growth of n-type ZnO and p-type NiO thin films, p-NiO/n-ZnO ultravilot detector were fabricated by us firstly in China, the maximum responsivity of 0.09 A/W was located at the wavelength of 360nm.At the last of the thesis, the whole conclusion of the thesis were given, ZnO-based thin film and devices were given a prospect.