AVS 50th International Symposium
    Electronic Materials and Devices Thursday Sessions
       Session EM-ThM

Paper EM-ThM8
Compositional Shift in Al@sub x@Ga@sub 1-x@N Induced by Reaction with Metallic Thin Films

Thursday, November 6, 2003, 10:40 am, Room 321/322

Session: Materials for Interconnects and Contacts to Semiconductors
Presenter: B.A. Hull, The Pennsylvania State University
Authors: B.A. Hull, The Pennsylvania State University
E.D. Readinger, The Pennsylvania State University
S.E. Mohney, The Pennsylvania State University
U. Chowdhury, The University of Texas at Austin
R.D. Dupuis, The University of Texas at Austin
Correspondent: Click to Email
The increasing use of AlGaN in group III nitride devices calls for further advances in our understanding of the chemistry of contacts to this alloy semiconductor. Interfacial reactions between the metals Ni, Pd or Au and Al@sub x@Ga@sub 1-x@N (0.15 < x < 0.6) have been studied for annealing temperatures of 250 to 900°C. X-ray photoelectron spectroscopy indicates that the Al to Ga ratio within the Al@sub x@Ga@sub 1-x@N directly beneath the contact metal increases, in some cases dramatically. Elemental profiles across the interfaces of annealed Ni/Al@sub 0.47@Ga@sub 0.53@N samples obtained by scanning transmission electron microscopy confirm the Al-enrichment near the interface. The Al-enrichment is consistent with thermodynamic modeling, which indicates that the AlGaN composition is favored to shift towards the more stable of the two binary nitride components (AlN). Less severe annealing conditions result in smaller compositional shifts; however, a very narrow annealing temperature range (750°C to 825°C) was required to induce extensive compositional shifts (greater than 5% increase in x), regardless of the initial Al@sub x@Ga@sub 1-x@N composition, indicating that extensive reaction is limited by the slow diffusion of Ga and Al within the AlGaN rather than the thermodynamic driving force for reaction. These compositional shifts can be expected to significantly impact the electrical properties of contacts annealed at high temperature due to the strong dependence of the band gap and Schottky barrier height on the AlGaN composition. We have correlated these reactions to the electrical characteristics of annealed ohmic contacts to p-type AlGaN as well as the thermal stability of Schottky contacts to n-type AlGaN.