AVS 52nd International Symposium
    Electronic Materials and Processing Wednesday Sessions
       Session EM-WeA

Paper EM-WeA1
Effect of Si on the Ohmic Behavior of Ti/Al/Mo/Au Metallization for AlGaN/GaN HEMTs

Wednesday, November 2, 2005, 2:00 pm, Room 309

Session: Contacts to Semiconductors
Presenter: F.M. Mohammed, University of Illinois at Urbana-Champaign
Authors: F.M. Mohammed, University of Illinois at Urbana-Champaign
L. Wang, University of Illinois at Urbana-Champaign
H.J. Koo, University of Illinois at Urbana-Champaign
I. Adesida, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
The high breakdown voltage and high saturation current of AlGaN/GaN HEMTs present great potential for applications in power amplification. High performance devices for such application require low parasitic ohmic contact resistance. We present an investigation on the study of the effects of Si incorporation in Ti/Al/Mo/Au metallization scheme. Si is a commonly used n-type dopant in GaN alloys systems, and implantation and diffusion doping are utilized to increase carrier concentration at the surface of epilayers. In Ti/Si-based contact metallizations, the formation of TiSi@sub x@ at the interface is believed to lower the barrier height for conduction of current across the metal/GaN junction. In this study, we have carried out experiments to optimize the thicknesses of Si introduced in the metallization scheme. Impact of the place of insertion within the metallization scheme (e.g. Ti/Si/Al/Mo/Au vs. Ti/Si/Al/Si/Mo/Au) has also been studied. Si incorporation, surface treatment, and annealing are collectively optimized to induce a reduction in contact resistance. An example is the optimized Ti/Si/Al/Si/Mo/Au metallisation annealed at 850 @super o@C for which a contact resistance (R@sub c@) and specific contact resistivity (@rho@@sub c@) as low as 0.16 ± 0.02 @OMEGA@.mm and 6.77 ± 0.7 x 10@super -7@ @OMEGA@.cm@super 2@ were obtained, respectively. This represents a significant reduction when compared to what was correspondingly obtained for Ti/Al/Mo/Au at 0.41 @OMEGA@.mm and 4.78 x 10@super -6@ @OMEGA@.cm@super 2@, respectively. Atomic force microscopy (AFM) and Auger electron spectroscopy (AES) characterization are utilized to reveal the nature of ohmic contact formation and the evolution in surface morphologies of the metallization schemes and epilayers.