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

Paper EM-WeA8
Chemically-Induced Point Defects and Schottky Barrier Formation at Metal/4H-SiC Interfaces

Wednesday, November 2, 2005, 4:20 pm, Room 309

Session: Contacts to Semiconductors
Presenter: L.J. Brillson, The Ohio State University
Authors: L.J. Brillson, The Ohio State University
S. Tumakha, The Ohio State University
M. Gao, The Ohio State University
S. Tsukimoto, Kyoto University, Japan
M. Murakami, Kyoto University, Japan
D.J. Ewing, Carnegie Mellon University
L. Porter, Carnegie Mellon University
Correspondent: Click to Email
We have used depth-resolved cathodoluminescence and Auger electron spectroscopies, DRCLS and AES, respectively, to determine the role of chemically-induced defects on 4H-SiC barrier formation on a nanometer scale. DRCLS of 5 nm Au, Ag, Ti, and Ni overlayers reveal formation of mid-gap defect transitions at ~1.8 eV and 2.85 eV extending only nanometers away from the junction. These states vary in their ranges of depth and depend sensitively on interface reactivity and subsequent UHV annealing. Their pervasive appearance near morphological defects and the absence of new gap states indicates that native defects rather than metal-specific states produce the dominant interface levels. For thicker TiAl Ohmic contacts with 5 min 1000 C anneals, cross-sectional scanning electron microscopy, AES, and DRCLS reveal a continuous ternary Ti-Si-C interfacial layer ~100 nm thick, a 1.9 eV sub-band gap transition localized within this depth and a 2.8 eV emission extending into the SiC, indicating both reaction-induced compound and defect formation, respectively. Within annealed NiTiAl Ohmic contacts, Ni silicide and Ti carbide form with a qualitatively different ~ 1.6 eV transition extending beyond the reaction zone. AES showing C movement from SiC into the metal overlayer indicate formation of a C-deficient SiC point defect. Thus the major difference in TiAl and NiTiAl interfacial reactions induces different interfacial gap states. For Ni/SiC reacted diodes, DRCLS and current-voltage measurements show a close correspondence between the Schottky barriers and deep level defect energies from diode to diode. Furthermore, the range of energies bounded by these defects corresponds with Schottky barrier heights reported previously via electrical measurements. This correspondence between chemically-induced deep levels at bulk defect energies and the range of macroscopic Schottky barriers for SiC appears to be a more general phenomenon, extending to other compound semiconductors as well.