| dc.description.abstract | This thesis primarily focuses on the study of gallium nitride ohmic contacts, discussing the characteristics of graphene and recessed ohmic contacts. The research includes the graphene transfer process and analyzes the effects of different surface treatments and annealing temperatures on graphene using Raman spectroscopy. Additionally, the changes in interface barrier height are examined by employing a transfer length method after inserting a graphene layer. Finally, the combined graphene and recessed ohmic contact AlGaN/GaN HEMT are analyzed for their DC electrical properties and contact resistance improvement.
After oxygen plasma treatment on the graphene surface, the adhesion of metal electrodes is enhanced. Experimental observations reveal a significant increase in graphene′s hydrophilicity after a brief oxygen plasma treatment. However, the Raman spectroscopy analysis shows increased defects following the oxygen plasma treatment. This study also investigates the impact of annealing temperatures ranging from 300 °C to 850 °C on graphene. Through Raman spectroscopy analysis in a nitrogen environment, the temperature-induced defect increase is observed to occur between 400 °C and 500 °C.
Conventional high-electron-mobility transistors based on gallium nitride typically undergo high-temperature annealing to form better ohmic contacts. The specific contact resistivity (ρc) of the conventional specific ohmic contact is 7.3×10-5 Ω·cm2. Introducing graphene into the ohmic contact region can effectively reduce its specific contact resistivity to 8.1×10-6 Ω·cm2. Through transfer length method analysis and fitting observations, the interface barrier height in the thermionic field emission (TFE) model is reduced from 1.02 eV for the traditional ohmic contact to 0.83 eV for graphene insert layer ohmic contacts, explaining the decrease in contact resistance.
Recessed ohmic contacts have also been proven to be an effective method for reducing ohmic contact resistance. In this study, 2×48 μm2 rectangular recesses are introduced, and graphene insert layer, effectively reducing the contact resistance to 1.36 Ω·mm. Compared to the traditional ohmic contact resistance of 4.13 Ω·mm, this represents a 67.1% reduction. Furthermore, introducing oxygen plasma treatment during fabrication effectively removes the additional current paths caused by graphene, allowing the device to achieve good on/off characteristics. | en_US |