Development of Liquid Phase van der Waals Contact Formation between 2D Semiconductor and Metal Electrode

Abstract

Two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) have been studied as promising materials for future electronic and optoelectronic applications. However, physical vapor deposition (PVD) methods, a representative conventional metallization approach, have several problems when applying 2D semiconductors to advanced and novel device applications. First, PVD methods usually involve “high energy” metal atoms or cluster bombardment on the samples, which can damage the atomically thin 2D semiconductors and cause various non-ideal phenomena such as Fermi level pinning. Second, these methods require expensive, dedicated equipment and restrict the use of materials that are vulnerable to heat or vacuum. Third, they have difficulty depositing metals uniformly on complex-shaped 3D surfaces. Here, I present that facile and low-energy integration of metal electrodes with 2D semiconductors can be achieved by an electroless deposition process, which occurs at room temperature and in a liquid phase. Field-effect transistors (FETs) using monolayer MoS2 grown by chemical vapor deposition (CVD) were fabricated through electroless silver deposition, and they clearly showed n-type semiconducting properties of monolayer MoS2 with a field-effect mobility of 7.17 cm2V-1s-1 and an on/off ratio of 10^7. Raman and photoluminescence analyses demonstrated that MoS2 was not significantly damaged during the electroless deposition process. A peel-off test, X-ray photoelectron spectroscopy (XPS) spectra, and cross-sectional transmission electron microscopy (TEM) images confirmed that electroless deposition causes less damage to and chemical interaction with TMDs than evaporation methods and approaches van der Waals contact. I expect that further development of the electroless deposition methods for 2D semiconductor devices will provide a facile way to form van der Waals contacts for advanced and novel applications.