Hongfei Li1 Yuzheng Guo2 John Robertson1

1, University of Cambridge, Cambridge, , United Kingdom
2, Swansea University, Swansea, , United Kingdom

The high mobility semiconductor Ge is limited by the high resistance of its n-type contacts due to the Fermi level pinning (FLP) of Schottky barriers (SBs) close to the valence band maximum (VBM). It turns out that this pinning occurs only for SBs of elemental metals whereas the compound metals like germanides and silicides have a different experimental behavior [1]. This ‘extrinsic behavior’ in which the Schottky pinning factor, S, depends on both metal and semiconductor facet is potentially very useful and can be exploited to reduce the large n-Ge SBH. We studied this SBH effect using density functional supercell calculations. The S factor is found to vary from 0.5 to 0.3 for silicides on Si(100) to Si (111), and to 0.3 to 0.2 for germanides on Ge(100) to Ge(111), with also a strong dependence of the effective charge neutrality level’ on the facet. This behaviour is found to be consistent with early experimental results for Si(100) and Si(111) of Tung [2]. Interestingly, it contradicts some later experimental data for Ge [3], however the ability to make abrupt epitaxial Ge/germanide interfaces is much more difficult for the germanide system than for silicides [3], and it is proposed that the calculated germanide results are used as guidance for the Ge system.
[1] T Nishimura, T Yajima, A Toriumi, APX 9 085201 (2016)
[2] R Tung, JVST B 11 1546 (1993)
[3] P S Y Lim, Y C Yeo, APL 101 172103 (2012); Y Deng, S Zaima, Thin Solid films 557 84 (2014)