Effect of Cl[sub 2] Plasma Treatment on Metal Contacts to n-Type and p-Type GaN

The effect of surface treatment using Cl 2 inductively coupled plasma on ohmic contacts to both n-type and p-type GaN was investigated via synchrotron photoemission spectroscopy. Compared to HCl treatment, the Cl 2 plasma treatment led to a shift of the surface Fermi level by 1.0 eV toward the conduction band maximum for n-type GaN and by 0.8 eV toward the valence band minimum for p-type GaN. N vacancies were produced near the surface by the plasma treatment, playing a role in reducing the surface band bending of n-type GaN, and thereby causing a dramatic decrease in contact resistivity. A significant degradation in the ohmic contact to p-type GaN could be attributed to an n-type layer formed near the surface region of the p-type GaN after the plasma treatment. The n-p junction formed below the surface led to an increased Schottky barrier for the transport of holes.