AVS 53rd International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuA

Paper EM-TuA6
Boride-based Schottky Contacts to p-GaN

Tuesday, November 14, 2006, 3:40 pm, Room 2003

Session: Materials for Power Electronics
Presenter: L.F. Voss, University of Florida
Authors: L.F. Voss, University of Florida
L. Stafford, University of Florida
J.-J. Chen, University of Florida
S.J. Pearton, University of Florida
F. Ren, University of Florida
Correspondent: Click to Email
An important aspect of the improvement of GaN-based devices for high temperature/high power electronic devices is the development of more reliable and thermally stable Ohmic and Schottky contacts on both n-type and p-type GaN. While the most common Schottky contacts to GaN are based on Ni/Au and Pt/Au, there is an increasing interest for metallization schemes with higher melting temperatures and better thermodynamic stability. In this work, we examine the potential of boride-based Schottky contacts to Mg-doped GaN layers grown by Metal Organic Chemical Vapor Deposition. This investigation is realized using current-voltage (I-V), x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy measurements. It is found that W2B and W2B5-based Schottky diodes exhibit an excellent thermal stability upon annealing up to ~500°C. At higher annealing temperatures, the diodes show deterioration in rectifying behavior due to the onset of metallurgical reactions with GaN. On the other hand, the temperature dependence of the I-V characteristics indicates that tunneling through a Schottky barrier (thermionic field emission) is the dominant transport mechanism of the diodes under forward bias conditions. The characteristic energy related to the tunneling probability is however higher (E@sub0@~80 meV) than that expected from the concentration of Mg acceptors alone (E@sub0@~50 meV). This is found to correlate with the presence of acceptor-like defects in the p-GaN surface vicinity that enhance the tunneling probability (defect-assisted tunneling). This high concentration of defects is also believed to explain the unexpectedly high barrier heights extracted from the tunneling model (~4.5 eV) which is higher than that deduced from the heterojunction band offsets obtained from XPS measurements. The possible mechanisms for reverse-bias current are also discussed.