Contact engineering of layered GeAs film for thin channel field-effect devices

A p-type semiconductor for layered materials is yet to be established despite MoS2 being the leading candidate for n-type semiconductors. GeAs (layered IV-V compound) is a stable and pure p-type material with the resistivity of 1-3×10-2 Ωcm. GeAs contains no unusual constituent elements for semiconductor materials, which lowers the barriers to fabricating and utilizing GeAs film. In this study, the device structure of GeAs field-effect transistors (FETs) was investigated in terms of electrical contacts. The resistivity of a two-terminal device fabricated with an exfoliated film was reduced by approximately three orders of magnitude by inserting a metallic NbS2 buffer layer at the electrode interface. The resistivity of the two-terminal device was maintained for the thick and thin films by introducing three-dimensional (3D) contact structures. The FET performances of the GeAs channel were demonstrated in top-gate devices comprising 3D contact structures and high-κ dielectric. Based on these characteristics, the contact resistance was estimated using the Y-function method, which yielded values equivalent to those obtained using advanced contact technologies for WSe2, which is a promising p-type semiconductor. These findings expand the options for p-type semiconductors in two-dimensional materials.