Preparation Of Zno Materials And Study Of Gan-based Led Devices

Zinc oxide (ZnO) and gallium nitride (GaN), the same as wide band gap semiconductor materials, have similar crystal structure and photoelectric properties. There are two parts to make a relevant research to ZnO and the GaN materials (or devices) in this thesis.The First PartAs a novel multi-functional direct wide band gap semiconductor materials, ZnO has excellent optics, electricity, mechanical properties, chemistry stability and thermal stability. Doped ZnO thin films have high transmittance at visible light wavelengths and low resistivity, makes it become a kind of excellent electrode material. The preparation process and properties of ZnO thin films and Y doped ZnO thin films prepared by sol-gel synthesis were preliminary studied in this thesis.In this thesis, ZnO thin films and Y doped ZnO thin films prepared by sol-gel synthesis were studied. Some interesting results are as follows:1. ZnO thin films with good c-axis preferred orientation were obtained in such process parameters in sol-gel synthesis:48h of aging time,300℃of the preheating temperature and 500℃of annealing temperature. The preheating temperature mainly affected the nucleation, and the annealing temperature determined the crystal structure of ZnO. With the increase of coating layers, the growth mode of ZnO thin films changed from layer growth to island growth, resulting the c-axis preferred orientation of ZnO thin films decreased. The light transmission rate of ZnO thin films as-prepared was over 85% in the visible range (λ> 390nm). Band gap of ZnO thin films was 3.26eV, calculated by Tauc mapping. Violet light, blue light, green light, yellow light were observed in the photoluminescence spectra of ZnO thin films. Violet light came from direct radiation of the conduction band and the valence band. Blue light, green light, yellow light were related to defect.2. Y doped ZnO thin films had lower crystal structure and transmittance. Crystal lattice distortion and defects turned up, when Y took the place of Zn in the ZnO lattice.3. There were two competing mechanism in the resistivity of Y doped ZnO thin films. The resistivity of Y doped ZnO thin films was minimum about 30Q.m, when the dopant concentration was between 0.5at% and 1at%.The Second PartThere are still two problems to overcome that semiconductor solid state lighting based on LED replaces traditional light sources on the stage, one is cost, the other is the brightness issue. At present, commercial GaN-based LED devices are primarily grown on heterogeneous substrates by MOCVD, such as sapphire (Al2O3) substrate, silicon carbide (SiC) substrate, silicon (Si) substrate. Owing to the requirements for high-brightness LEDs, it needs to be made into vertical structure devices for the three kinds of substrates technology. In this thesis, Considering the low cost advantages of GaN on Si substrate and the good thermal performance of metallic substrate, GaN based LED grown on Si substrate with vertical-structure and electropalting metallic-substrate were successfully prepared, the photoelectric properties and stress in fabricating were studied. Some interesting results are as follows:1. X-ray diffraction analysis showed that the electropalting metals had preferred orientations, Pt electrode layer, Au and Cu electropalting layer with (111) crystal plane, and Cr electropalting layer with (110) crystal plane.2. X-ray diffraction and photo luminescence spectra analysis about electroplating metallic substrate GaN-based LED films showed that the tensile stress which GaN-based LED films grown on Si substrate were under decreased by transferring to electroplating metallic substrate, even turned compressive stress. The compressive stress was reduced to almost no stress, and the Quantum Confined Stark Effect of InGaN quantum well layer also weakened in subsequent chip fabricating process.3. The test results of photoelectric properties showed that the working voltage was 3.45V, the light output power of Pt electrode LED chip without silicone and lens was 115mW, and that of Ag electrode LED chip was 245mW@350mA in as-prepared electroplating metallic substrate GaN-based blue LED. In our samples, the light output power with the current had good anti-saturation performance and the wavelength with the current had good stability, showing 2nm red-shift in the test range. The yield of electroplating metallic substrate GaN-based LED was about 60%.This work was supported by the National 863 Project and the research foundation of the Education Ministry Innovation Team for Semiconductor Illumination Technology.