Effects of plasma treatment on the Ohmic characteristics of Ti/Al/Ti/Au contacts to n-AlGaN

The effects of surface treatment using Cl-2/BCl3 and Ar inductive coupled plasmas on the Ohmic characteristics of Ti/Al/Ti/Au contacts to n-type AlxGa1- xN (x= 0-0.5)were investigated. Plasma treatment significantly increased the surface conductivity of GaN and Al0.1Ga0.9N, leading to improved Ohmic behaviors of the contacts. However, it reduced the surface doping level in AlxGa1-xN (x >= 0.3) and degraded the contact properties. Following a 900-1000 degrees C anneal, the Ti/Al/Ti/ Au contacts to AlxGa1-xN (x= 0-0.5) became truly Ohmic, with specific contact resistances of (3-7) x 10(- 5) Omega cm(2), whereas the contact to Al0.5Ga0.5N remained rectifying even without the plasma treatment. X-ray photoelectron spectroscopy measurements confirmed that the Fermi level moved toward the conduction band in GaN after the plasma treatment, but it was pinned by plasma-induced deep-level states in Al0.5Ga0.5N. This study emphasizes the need to mitigate plasma damage introduced during the mesa etch step for AlGaN-based deep-UV emitters and detectors. (c) 2006 American Institute of Physics.