The Research On Characterization Method And Process Dependency Of GaN MOSFET

GaN has larger bandgap, breakdown voltage, electron saturation velocity which made it have great potential to be applied for high temperature, high power and high frequency electronics compared to traditional Si. AlGaN/GaN HFET have been developed, but its normally-on operation made its power consumption higher. As GaN MOSFET can realize normally-off operation, it has become one of the most attractive research topic in latest years. However, the channel mobility of GaN MOSFETs are still very low. Also, problems of misestimate on mobility still exist. In this condition, to optimize the fabrication process of GaN MOSFETs and characterize the mobility properly is one important research topic.In my study, there are two parts, the study of mobility characterization and the study of process dependency. In characterization process, a phenomenon of parallel channel caused by worse field isolation was found in bar-type GaN MOSFETs. It will result a phenomenon of two-piece mobility and overestimation of the mobility extracted by C-Gm method. On the other hand, the channel length would be larger than the designed size by dry recess process. It will lead an obvious underestimation on mobility. We have presented an improved method to characterize the mobility of the short channel MOSFETs. The mobility of152.3cm2V-1s-1extracted by our method agreed quite well with that of a long channel ring type MOSFET which was thought to be reasonable. In the fabrication process, different kinds of device structure and process conditions were utilized. The results showed that GaN MOSFET on n-type doped heterostructure has higher mobility and lower interface state density which demonstrate that it is a better candidate for realizing GaN MOSFET. Also, dry recess experiment with different ICP etching conditions was done. Trenching effect at the bottom of sidewall was observed and analyzed. Optimum ICP condition was found to gain a better recess profile with uniform depth. Also, GaN MOSFET fabricated by optimized ICP condition have maximum mobility of151cm2V-1s-1and the minimum interface state density of1.31×1011cm-2eV-1.The results of this study demonstrate that, the mobility characterization method presented in our study can properly extract the mobility in device with dimensional variation. Also, with optimized device structure and ICP dry recess condition, the channel mobility was improved.