Theoretical and Experimental Approach to Developing Improved Electrical Contacts to GaN

摘要

The metallurgy and electrical performance of contacts to GaN were examined. Thermodynamic estimates coupled with experimental work revealed clear trends in the nature of the contact metallurgy depending upon the position of the metal in the periodic table. This information was then used to aid in the investigation and design of electrical contacts to GaN. Ohmic contacts to n-GaN, Schottky barriers to n-GaN, and ohmic contacts to p-GaN were fabricated and characterized. These studies resulted in an improved understanding of the mechanism of ohmic contact formation in Al/Ti/n-GaN contacts, along with the development of TiN/Ti/n-GaN and ZrN/Zr/n-GaN ohmic contacts with exceptional thermal stability at 600 deg C and contact resistivities of 6 x 10(exp -6) and 2 x 10(exp -5) ohm.sq cm, respectively, for n = 7 x 10(exp 17) cu cm. Also developed were Re/n-GaN Schottky barrier contacts that were stable upon annealing at 700 deg C with current-voltage and capacitance-voltage barrier heights of 0.82 and 1.06 eV, respectively. For ohmic contacts to p-GaN, a large number of contacts were evaluated. A clear improvement over conventional Au/Ni/ p-GaN contacts was provided by electrodeposited Pt/p-GaN and sputtered Pt/Ni/p- GaN contacts, which provided contact resistivities that were lower than Au/Ni/p- GaN contacts by more than a factor of two. An explanation for this improvement was formulated.