Effects of W diffusion barrier on inhibition of AlN formation in Ti/W/Al ohmic contacts on N-face n-GaN

Abstract

We investigate the effect of W diffusion barrier in Ti/W/Al ohmic contacts formed on N-face n-GaN. The contacts exhibit contact resistivity of as low as 2.3 x 10(-4) Omega cm(2) and better thermal stability than Ti/Al contacts. Cross-sectional transmission electron microscopy micrographs reveal that in-diffused Al atoms on the n-GaN surface react with N atoms to form an AlN layer in Ti/Al contacts, resulting in upward band bending, and consequently, a high contact resistivity. The use of a 10-nm-thick W layer suppresses the in-diffusion of Al atoms to n-GaN, thereby preventing the formation of AlN and enhancing the thermal stability of Ti/W/Al contacts. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665623]