Access Type

Open Access Dissertation

Date of Award

January 2021

Degree Type


Degree Name



Physics and Astronomy

First Advisor

Zhixian Zhou


Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDs) have emerged as a promising candidate for post-silicon electronics. Few-layer tungsten diselenide (WSe2), a well-studied TMD, has sown high hole mobility and ON/OFF ratio in field effect transistor (FET) devices. But the n-type performance of WSe2 is still quite limited by the presence of a substantial Schottky Barrier. Palladium diselenide, (PdSe2) is a newly discovered TMD that is of interest because of its high electron mobility, and moderate ON/OFF ratios. However, despite its relatively small bandgap, the n-type performance of few-layer PdSe2 FETs has also been limited by a Schottky barrier, which is likely due to Fermi-level pinning. In this work, we report high performance n-type FETs enabled by a few-layer WSe2/PdSe2 heterojunction. We show that the current through few-layer WSe2 or PdSe2 alone is quite small, but across the heterojunction WSe2 serves as a “buffer layer” at the drain/source contacts for few-layer PdSe2 FETs. We observe a high ON/OFF ratio of 105, with an electron mobility of ~139 cm2 V-1 s-1. The mobility continues to rise at cryogenic temperatures, indicating a substantial reduction in the Schottky Barrier height. A heterojunction consisting of 3-layer PdSe2 and 3L WSe2 showed an ON/OFF ratio approaching 107, while still maintaining a moderate mobility of ~ 57 cm2 V-1 s-1. We believe the significantly improved device performance enabled by our contact engineering technique will facilitate further study of the intrinsic properties of few-layer 2D materials.