Fabrication And Study Of Heterojunction Light-emitting Diodes Based On GaN And ZnO Material

With the development of photoelectronic industry in recent years, Zinc oxide and Gallium Nitride, as representitives of II-VI group and III-V group compound semiconductor materials, have attracked great attention and been greatly researched. Zinc oxide has excellently opticcal and electrical characters due to its wide band-gap of 3.37eV and relatively large exciton binding energy of 60meV at room temperature (RT). Even though unintentionally doped Zinc oxide shows a n-type property, it can not be directly used to form devices. It needs to be intentionally doped to realize p-type conductivity. GaN is also a kind of directly wide band-gap semiconductor material with 3.39eV band-gap energy. Unintentionally doped GaN also shows n-type with more than 1018cm-3 carrier density. It's not hard to achieve n-type doped GaN material, and the technology is relatively mature. But how to get reliable n-type doped GaN material was a hard problem which was just solved in recent years. As mentioned above, some properties of ZnO and GaN are similar. With the further researching in optoelectronic technology, n-ZnO/p-GaN heterojunction has become a new subject. In this work, we studied about n-ZnO/p-GaN related heterojunctions and our work contains two parts:1, The fabrication of n-ZnO/p-GaN heterojunction light-emitting diodes. First, we got p-GaN epitaxy layer on c-aspect sapphire through Metal-Organic Chemical Vapor Deposition (MOCVD) method. Then we use another MOCVD equipment to grow n-type doped ZnO film on p-GaN layer to form n-ZnO/p-GaN heterojunction. With wet-etching method and fabricating of ohmicelectrodes, we got n-ZnO/p-GaN heterojunction light-emitting diodes. Electrical test shows representativeⅠ-Ⅴcharacteristics. We found peak wavelength of 401nm under electroluminescence (EL) emissions test, and we proved that the light emitting happened in p-GaN layer with Anderson model.2, The n-ZnO/AlGaN/p-GaN heterojunction light-emitting diodes. We used the same method with part 1 to produce p-GaN epitaxy layer. Then, we grew 15nm AlGaN on p-GaN as electron blocking layer. Finally, we achieve n-ZnO/AlGaN/p-GaN heterojunction through growing 500nm n-type ZnO film on AlGaN layer. We achieved the Ultraviolet light emitting under electroluminescence (EL) emissions by introducing AlGaN Electron Blocking Layer between n-ZnO and p-GaN. The n-ZnO/AlGaN/p-GaN heterojunction presents a representative current rectification property with the threshold voltage of 15V. The emitting light is relatively strong near-Ultraviolet. Comparing the electroluminescence (EL) spectra of n-ZnO/AlGaN/p-GaN heterojunction and n-ZnO/p-GaN heterojunction, we proved that the introduction of AlGaN layer has effectively restricted the injection of electrons from ZnO layer to GaN layer, which is also theoretically supported by Anderson model.