Investigation Of Basic Properties Of Sb Doped ZnO Films And ZnO Homojunction Light Emitting Devices By MOCVD

Zinc Oxide (ZnO) is a new type direct wide bandgap semiconductor which has lower growth cost and higher exciton bonding energy. Due to these properties, ZnO has great potential application in short wavelength light emitting devices, laser devices and detecters etc. Therefore ZnO has become a research hotspot. Although there are some reports about ZnO light emitting diodes (LED) and laser diodes (LD), the properties are still far away from practical application. The p-type doping mechanism is still unclear. It is hard to grow reprduceable, stable and high quality p-type ZnO film. These are still major problems which blocked the application of ZnO.In this thesis, the Sb doped ZnO films were fabricated using Sb metal organic compound as doping source by MOCVD. Firstly, the influence and its mechanism of Sb doping in ZnO have been investigated in different doping concentration ranges. Then the properties of Sb doped p-type ZnO films on c-sapphire as well as its p-type doping mechanism are also investigated. Lastly, ZnO homojunction LEDs are fabricated based on ZnOp-type doping and the electroluminescence (EL) are also observed at room temperature.The surfactant effect of Sb doping in ZnO growth by MOCVD is investigated. Its mechanism is also discussed. Firstly, the Sb doping concentration has been changed in a small range under optimized growth condition. It is found Sb doping could suppress the deep level emissions in photoluminescence (PL) spectra of ZnO. It can also change the surface morphology and increase the grain size of ZnO. After analyzing the data and references, we think the influence of Sb doping on the properties of ZnO could be explained by surfactant effect of Sb in ZnO growth. Sb surfactant could enhance the diffusion of O adatom on the growing surface. This enhancement can lead to influence in two aspects:firstly, it can suppress the formation of interstitial oxygen (Oi) and reduce the deep level emission in PL spectra; secondly, the enhancement of O adatom diffusion could form a zinc rich environment on the growing surface under O rich condition which will increase the lateral growth and improve the surface morphology. The improvement of properties by Sb surfactant could lay the foundation for future application of ZnO.The stress introduced by Sb doping and its influence on ZnO optical properties are investigated. Firstly, the mol flow ratio of Sb doping source and Zn source has been changed drastically. It is found that the Sb doping concentration can not be increased unlimitedly. ZnO film is still fabricated even when the mol flow ratio of Sb doping source and Zn source reach 1:2. No Sb related compound is fabricated. The optical band gap of ZnO showed a blueshift with the increase of Sb doping concentration. The blueshift should be from the stress introduced by Sb doping. The band gap increases linearly with the stress introduced by Sb.Sb doped p-type ZnO films are fabricated on c-sapphire using Sb organic doping source by MOCVD. The p-type formation mechanism is also discussed. The structure, electrical and optical properties of Sb doped ZnO films with different growth temperature are investigated. The growth temperature window for high quality Sb doped ZnO is obtained. Then Sb doped p-type ZnO films are grown on c-sapphire using organic Sb doping. The hole concentration, resistivity and mobility are 1.14×1017/cm3,0.49Ω·cm and 1.80 cm2/V·s, respectively. According to the XPS data, Sb is supposed to subtitude Zn to form a Sbzn-2Vzn accepter complex. Accepter related peaks are observed in low temperature PL measurement. Accepter bonding energy is obtained as 124 meV. In commercial MOCVD technology, onganic source is an efficient and controllable doping source. Realization of ZnO p-type doping in MOCVD using organic doping source paves the way for ZnO future application.Horizontal structure ZnO homojunction LED is fabricated on c-sapphire using organic doping source by MOCVD. Sb doped p-type ZnO layer was grown on high quality undoped n-type layer on c-sapphire. NH4CI is used to etch masked ZnO film to n-type layer to form the step. Au-Zn and Au-Ni alloy electrodes are deposited on n-type and p-type layer, respectively. The forward turn-on voltage and reverse breakdown voltage are 3.3 V and greater than 5.0 V, respectively. Obvious electroluminenscence (EL) spectra with three peaks at 3.0 eV,2.31 eV and 1.74 eV are observed from the device under forward injection current. Realization of ZnO homojunction LED on c-sapphire using organic doping source by MOCVD directly comfirm the application feasibility of ZnO in semiconductor lighting.Vertical structure ZnO homojunction LED is fabricated on P doped n+Si substrate. ZnO p-type layer is formed by diffusion of P from Si substrate. Al back electrode and Au-Zn alloy electrode are deposited on Si and ZnO top surface, respectively. The forward turn-on voltage and reverse breakdown voltage are 4.2 V and greater than 6.0V, respectively. Obvious EL band centered at 470 nm is observed from the device under forward injection current. Si substrate has great application prospect due to its mature technology, lower cost and good electroconductivity and themalconductivity.