Low temperature gate dielectric deposition for recessed AlGaN/GaN MIS-HEMTs

Gate dielectrics are of great interest in AlGaN/GaN transistors to increase the I_on/I_off ratios and to reduce gate leakage. However, integrating gate dielectrics with recessed gates require low temperature dielectric depositions where the gate photoresist is patterned and the gate is recessed before dielectric deposition. This study aims to characterize gate insulators deposited by low temperature atomic layer deposition (ALD) processes. HfO₂ and Al₂O₃ were deposited at temperatures ranging from 80°C to 120°C and annealed under different ambient and temperature conditions. MIS-HEMTs with HfO₂ gates showed excellent I_on/I_off ratios of over 10⁹ and subthreshold slopes of 71 mV/dec, which is superior to reference transistors with Schottky gates. Therefore, low temperature gate dielectrics promise to be an enabling technology for MIS-HEMTs with both recessed and insulating gates.