Structural and electrical characteristics of Ag/Al_(0.2)Ga_(0.8)N and Ag/Al_(0.3)Ga_(0.7)N Schottky contacts: an XPS study

摘要

The effects of successive Ag depositions on Al_xGa_(1-x)N for x = 0.20 and x = 0.30 grown by metal-organo chemical vapour deposition (MOCVD) have been investigated using X-ray photoelectron spectroscopy (XPS). The interfacial chemistry and electron transport properties have been studied. We report Fermi shifts ΔE_F = -0.3 eV and ΔE_F = -0.4 eV to lower binding energies on Al_xGa_(1-x)N for x = 0.20 and 0.30 respectively, from the clean surface to the last Ag coverage. The effects of ex-situ hydrofluoric acid etch followed by in-situ 600℃ ultrahigh-vacuum (UHV) anneal have also been investigated. We show that a reduction in oxygen concentration at the surface for the two different Al concentrations may affect the surface band bending prior to metallization, hence altering the characteristics of the Schottky barrier. XPS characterization of Ag/Al_xGa_(1-x)N formed after the premetallization surface treatment shows that HF etching followed by UHV annealing produce abrupt, well-defined interfaces. These results are discussed in the context of current models of Schottky barrier formation.