Barrier height determination for n-type 4H-SiC schottky contacts made using various metals

Abstract

We have studied Schottky barrier contacts to n-type 4H-SiC with Cr, Mo, Ta, W, Au, and Ni. We have focused on effects of the metal work function, measurement technique and interface behavior on the Schottky barrier heights (SBHs). The contacts were prepared by metal deposition via high frequency cathodic sputtering on chemical vapor epitaxially grown epitaxial layers with low residual doping (2 × 1015 cm−3). Prior to deposition on Si-terminated surfaces, they were in-situ cleaned by Ar-ion sputtering for 5 and 10 min, respectively. The contacts have been characterized by means of current-voltage, capacitance-voltage (C-V), and internal photoemission (IPE) methods at room temperature. With deep level transient spectroscopy, interface deep electron traps have been detected with thermal ionization energies of 0.68, 0.77, and 1.04 eV, respectively. These traps have been attributed to structural defects formed during epitaxial growth termination. The diodes have relatively low reverse leakage current, but the ideality factor is larger than one. The SBHs have been determined from C-V and IPE measurements. It has been shown that the C-V data may contain errors resulting in a low SBH if electron deep traps are present in the interface region. In general, the SBH of various metals are influenced by the metal work function and also by the semiconductor surface preparation. The interface homogeneity is an important characteristic of the Schottky contacts, which may be improved by an optimized ion sputtering prior to metal deposition. We have considered the SBHs determined by IPE measurements as most reliable.