Ultralow Ohmic Contact in Recess-Free Ultrathin Barrier AlGaN/GaN Heterostructures Across a Wide Temperature Range

‘Ohmic-before-passivation’ process was implemented on ultrathin-barrier (UTB) AlGaN (<6 nm)/GaN heterostructure to further reduce the ohmic contact resistance (R_c). In this process, alloyed Ti/Al/Ni/Au ohmic metal was formed first, followed by AlN/SiN_x passivation contributed to restore two-dimensional electron gas (2DEG) in the access region. Due to the sharp change in the concentration of 2DEG at the metal edge, a reduced transfer length (L_T) consisted with lower R_c are achieved compared to that of ohmic contact on AlGaN (~20 nm)/GaN heterostructure with pre-ohmic recess process. Temperature-dependent current voltage measurements demonstrate that the carrier transport mechanism is dominated by thermionic field emission above 200 K and by field emission below 200 K. The ‘ohmic-before-passivation’ process enables the relative stability of ohmic contacts between 50 K to 475 K and significantly improves the DC characteristics of GaN-MIS-HEMTs, offering a promising means for scaling down and enabling the utilization of low-voltage GaN-based power devices in extreme environmental conditions.