n- GaN surface treatments for metal contacts studied via x-ray photoemission spectroscopy

The surface chemistry and electronic properties of n-GaN surfaces were studied via x-ray photoemission spectroscopy before and after wet chemical treatments. Shifts of the surface Fermi level were measured with the change in position of the Ga 3d core level peak. HCl treatment of n-GaN led to a 0.9 eV shift of the surface Fermi level toward the conduction band minimum, while KOH treatment led to a 0.3 eV shift of the surface Fermi level toward the valance band maximum. These shifts lead to a reduction in the surface barrier for HCl-treated n-GaN and for KOH-treated p-GaN, potentially improving contact resistance. The changes in surface chemistry indicate that a N (or Ga) deficiency with HCl(KOH) treatment alters the surface state density through the formation of donor (acceptor)-like states.