Realization of Fermi level unpinning and high-quality p-type contacts for 2D β-TeO2 by a built-in intercalation

Abstract

Contriving an industry-compatible method for fabricating purely high-quality p-type two-dimensional (2D) field effect transistors (FETs) has been proved to be pressing but challenging due to the strong interfacial coupling and thus tight Fermi level pinning (FLP). Herein, by employing density functional theory calculations, a straightforward but effective strategy is proposed to achieve high-quality p-type contact in few-layer TeO2–Pt junction by using a build-in intercalation to suppress the FLP and shield the damage from electrodes to the excellent electrical properties of TeO2 such as its ultra-high hole mobility. Specifically, the increase of TeO2 layer number will make the charge distribution of VBM and CBM be more lumped in the inner core layer, as a result, the outlying Te–O sublayer can act as an inserting layer like BN to protect the semiconducting electronic states and avoid gap-state pinning. Thus, as the TeO2 layer increases from 1 L to 3 L, (Ⅰ) strong FLP in metal-TeO2 interfaces is gradually unpinned; (Ⅱ) the polarity of Pt–TeO2 contact reverses from n-type to p-type; (Ⅲ) the excellent electrical properties of TeO2 such as hole effective mass is preserved as original despite strong charge transfer occurring at the interface. Besides, the tunnelling barrier at the interface is close to zero. This is quite different from introducing an extern BN intercalation, in which case the tunnelling through BN will prominently reduce the overall hole current. In addition, the contacts between 2D metal electrodes and monolayer TeO2 are found to obey the Schottky-Mott rule, and thereby p-type Ohmic contacts can be obtained at TeO2-VS2, -NbS2 interfaces. Whereas, a relatively large tunnelling barrier exists at the 2D metal-TeO2 interfaces. Our findings are quite essential and beneficial for designing high-performance p-type 2D FETs.