Schottky barrier height lowering and contact resistivity reduction via crystalline magnesium oxide interlayer on semiconductor surface

Abstract

The pervasive Fermi-level (FL) pinning at semiconductor surfaces severely limits the reduction of contact resistance, posing a critical challenge to the realization of high-performance nanoelectronic devices. In particular, germanium (Ge) inherently exhibits strong FL pinning, which results in high Schottky barrier height (SBH) and large contact resistance regardless of a metal work function. Here, interfacial dipole engineering for SBH modulation is realized by introducing a metal-interlayer-semiconductor structure employing crystalline magnesium oxide (MgO) as the interlayer. The insertion of MgO suppresses metal-induced gap states (MIGS) and partially reduces interface trap density through GeO2 formation, enabling significant FL unpinning. In addition, an extrinsic interfacial dipole is induced due to the charge neutrality level mismatch between MgO and Ge, further lowering the SBH. Crystallization of MgO enhances the passivation effect by suppressing unstable Ge suboxides and promoting stable GeO2 formation, resulting in an ultra-low SBH (< 0.05 eV), previously unreported. Moreover, with the improved conductivity of the MgO induced by crystallization, a specific contact resistivity as low as 8.38 x 10(-9) Omega<middle dot>cm(2) was achieved, corresponding to a reduction by a factor of 10(4) compared to that of a conventional metal-semiconductor contact. Also, systematic experiments using five different metals and comprehensive chemical analyses verify that both FL unpinning and extrinsic interfacial dipole formation are key mechanisms in SBH modulation. This study establishes a practical and scalable methodology for contact technique through favorable interfacial dipole formation, providing a viable pathway toward integration in next-generation nanoelectronic technologies.