Impact of Rapid Thermal Annealing Temperature of Cu-based ohmic stack on Performance of GaN MIS-HEMTs

In this study, we discuss the performance of Al2O3/AlGaN/GaN MIS-HEMTs with Cu/Al/Mo/Au ohmic stacks processed at different rapid thermal annealing (RTA) temperatures ranging from 600 to 800 °C. Substituting copper (Cu) for titanium (Ti) as the first metal in contact with the AlGaN layer, we explore the possibility of obtaining good ohmic contact at these relatively lower RTA temperatures. Lowering the RTA temperature leads to MIS-HEMTs exhibiting less hysteretic behavior, better stability and more positive threshold voltage. However, these improvements came with a downside, i.e., higher contact resistance, leading to lower maximum drain current. Our results, therefore, suggest trade-off between stability and power capability for GaN MIS-HEMTs employing Cu-based ohmic stack and could provide process guidelines for obtaining devices with desired characteristics.