In this work, we demonstrate the high-quality MBE heterostructure growth of various layered 2D materials by van der Waals epitaxy (VDWE). The coupling of different types of van der Waals materials including transition metal dichalcogenide thin films (e.g., WSe2, WTe2, HfSe2) and topological insulators (e.g., Bi2Se3) allows for the fabrication of novel electronic devices that take advantage of unique quantum confinement and spin-based characteristics. We demonstrate how the van der Waals interactions allow for heteroepitaxy of significantly lattice-mismatched materials without strain or misfit dislocations. Yet, at the same time, the VDW interactions are strong enough to cause rotational alignment between the epi-layer and the substrate, which plays a key role in the formation of grain boundaries.
We will discuss TMDs and TIs grown on atomic layer deposited (ALD) high-k oxides on a Si platform. WSe2 grown by MBE on ALD-grown Al2O3 on Si is demonstrated in field-effect transistors with back-end-of-line (BEOL) compatible fabrication temperatures (< 525 °C). Transistors exhibiting ambipolar behavior with drain currents exceeding 1mA/mm and ON-OFF ratios greater than 104 are demonstrated from the grown films. Field-effect hole mobilities greater than 40 cm2/V-s are measured, which is orders of magnitude higher than other MBE reported TMD mobilities and the highest to date for low-temperature grown TMDs. The achievement of relatively high-mobility transistor channels at BEOL compatible processing temperatures shows the potential for integrating transition metal dichalcogenides (TMDs) into CMOS process flows.
This work is supported in part by the Center for Low Energy Systems Technology (LEAST), one of six centers supported by the STARnet phase of the Focus Center Research Program (FCRP), a Semiconductor Research Corporation program sponsored by MARCO and DARPA. It is also supported by the SWAN Center, a SRC center sponsored by the Nanoelectronics Research Initiative and NIST.