Al ohmic contacts to HCl-treated MgxZn1-xO

The Al nonalloyed ohmic contacts were fabricated on MgxZn1 O-x (0 <= x <= 0.2) thin films. HCl surface treatment significantly reduced the specific contact resistances to value around 10(-4) Omega cm(2). X-ray photoelectron spectroscopy (XPS) analysis revealed that the HCl treatment increased the oxygen vacancy density and introduced chlorine to the semiconductor surface, resulting in a thin conductive layer and thus reduced specific contact resistance. A subsequent oxygen plasma treatment reduced the oxygen vacancy density, and correspondingly increased the specific contact resistance. Al-ZnO contacts were insensitive to the HCl treatment, due to the formation of a highly conductive At-doped thin interface layer.