Reduced Contact Resistance and Improved Transistor Performance by Surface Plasma Treatment on Ohmic Regions in AlGaN/GaN HEMT Heterostructures

A significantly reduced contact resistance and an improved DC and RF performance is demonstrated for AlGaN/GaN high electron mobility transistors by surface plasma treatments on ohmic regions in GaN‐based heterostructures. Various plasma processes using BCl3, Cl2, Ar, SF6, and their combinations are considered. While it is known that certain plasma treatments can remove native oxide and thereby reduce the ohmic contact resistance, detailed experiments are performed to further enhance the understanding. In addition, a second aspect of the plasma treatment is shown, where the controlled physical component of the etching process can improve the AlGaN surface morphology. This in turn can reduce the tunneling resistance for the carriers from the alloyed contact to the two‐dimensional electron gas. The contact resistance is found to decrease to 0.10 from 0.65 Ω mm for Ar, Cl2, and BCl3 treated sample in comparison to that of the control sample. The corresponding transconductance, saturation drain current, and unity current gain frequency are found to increase by 30, 37, and 41% for the high electron mobility transistors fabricated on the same sample. The authors report plasma treatments for very low contact resistances of 0.10 Ω mm. Controlled physical etching using Ar reduces the contact resistance when used in combination with other gases. This is due to the effective removal of oxide from the surface without increasing the surface roughness. It is further confirmed by the DC and RF performance improvement on HEMTs as shown in the figure.