The polarization field dependence of Ti/Al based Ohmic contacts on N-type semipolar GaN

Abstract

We report on the polarization field dependence of the Ti/Al based n-type contacts on various polar and semipolar GaN planes. The contact resistance of the metal contacts on N-face GaN could be lowered by photoelectrochemical (PEC) etching, which formed a pyramidal feature on the surface with {101¯1¯} facets. The contact resistance on the semipolar (101¯1¯) surface was 6.3 × 10−5 Ω cm2, showing even lower contact resistance than the PEC etched N-face when annealed at 450 °C. Among few semipolar planes, (101¯1¯), (112¯2¯), and (112¯2), the contact resistance was the lowest with (112¯2¯) plane, which is the plane with the stronger polarization field than (101¯1¯) and more Ga rich surface than (112¯2) plane.