The effect of N-polar GaN domains as Ohmic contacts

Transfer line method measurements revealed that if the Ohmic contact regions were replaced by N-polar GaN, the contact resistance could be reduced from 0.71 Ω mm (or ρc=4×10−6 Ω cm2) to 0.24 Ω mm for a ∼200 nm thick Si-doped GaN layer. The reduction in contact resistance was largely due to the ∼1019 cm−3 free carriers in N-polar source/drain regions as measured by Hall effect. Secondary ion mass spectroscopy confirmed that oxygen doping in the N-polar region was more than three orders of magnitude greater than that in the Ga-polar region that was explained by the large difference in the adsorption energy for oxygen (∼1.3 eV/atom) between the N- and Ga-polar surfaces during the metalorganic chemical vapor deposition.