Ultra-low resistance ohmic contacts to GaN with high Si doping concentrations grown by molecular beam epitaxy

Abstract

Ti/Al/Ni/Au ohmic contacts were formed on heavily doped n metal-polar GaN samples with various Si doping concentrations grown by molecular beam epitaxy. The contact resistivity (R C) and sheet resistance (R sh) as a function of corresponding GaN free carrier concentration (n) were measured. Very low R C values (0.09 Ω mm) were obtained, with a minimum R C of 0.035 Ω mm on a sample with a room temperature carrier concentration of ∼5 × 10 19 cm -3. Based on the systematic study, the role of R C and R sh is discussed in the context of regrown n GaN ohmic contacts for GaN based high electron mobility transistors. © 2012 American Institute of Physics.