Study on Fabrication of GaN thin films by RF Magnetron Sputtering Using Highly Purified Powders

There are many researches and methods to deposit a thin film of GaN. However, it is difficult to deposit GaN thin films, because high temperature and high vacuum are required. GaN thin film is fabricated usually by MOCVD or... [ view full abstract ]

There are many researches and methods to deposit a thin film of GaN. However, it is difficult to deposit GaN thin films, because high temperature and high vacuum are required. GaN thin film is fabricated usually by MOCVD or MBE as a film-forming method at the temperature of more than 800°C. On the other hand, MOCVD or MBE have a problem such as the safety and low deposition rate. In order to solve these problems, the deposing of GaN thin films by high speed RF magnetron sputtering using highly purified powders of GaN is examined in this study.

GaN powder of 99.999 % purity was used for the sputtering target. The deposition conditions were changed variously. The structural analysis, the observation of surface, and the temperature dependence of resistivity were carried out. The film was deposited on the sapphire single crystal at substrate temperatures between room temperature and 700°C. Both hexagonal and cubic structures were observed in a thin film. The existing ratio of each crystal structure was dependent of the substrate temperature. The crystallinity of hexagonal phase was higher than that for cubic one. Cubic phase was appeared at substrate temperature below 300°C. The both the resistivity and the temperature dependence of thin films was dependent on the substrate temperature. Both the resistivity and the activation energy for thin films deposited at 200°C were higher than those deposited at 700°C as shown in Fig.1. However, the activation energy for 200°C was about 0.75 eV and was ~1/4 of the band gap of GaN. This is caused by the doping of oxygen atoms in plasma in depositing a thin film. The activation energy of resistivity for the Si doped thin films were the same as those without Si, because the effect of oxygen doping was remarkable.