Nanopatterned Contacts to GaN

The effect of nanoscale patterning using a self-organized porous anodic alumina (PAA) mask on the electrical properties of ohmic and Schottky contacts to n-GaN was investigated with the aim of evaluating this approach as a method for reducing the specific contact resistance of ohmic contacts to GaN. The electrical characteristics of contacts to these nanopatterned GaN samples were compared with contacts to planar, chemically prepared (“as-grown”) GaN samples and reactive ion etched (RIE) GaN films without any patterning. The specific contact resistivities to unintentionally doped n-GaN using a Ti/Al bilayer metallization were determined to be 7.4 × 10⁻³ Ω cm² for the RIE sample and 7.0 × 10⁻⁴ Ω cm² for the PAA patterned sample. Schottky metal contacts with Pt and Ni were prepared on the three samples to validate the effects of RIE and nanopatterning on electrical behavior. The effective barrier height was decreased and the reverse current was increased significantly in the PAA patterned sample. The radius of curvature of the nanoscale corrugation in the patterned interface was smaller than the depletion width. The reduction of the depletion width at sharp corners enhanced the local tunneling current, reducing the specific contact resistivity and decreasing the effective barrier height. These results suggest that nanopatterning with PAA on GaN can significantly lower the contact resistance.