Control of Carrier Polarity and Schottky Barriers in Layered PdSe₂ Field-Effect Transistors

Palladium diselenide (PdSe2) has been discoveredasan intriguing two-dimensional (2D) semiconductor for its unique pentagonalcrystalline structure, electrical and optical anisotropy, thickness-modulatedband gap, robust air stability, and high carrier mobility, demonstratinggreat potential in field-effect transistors (FETs), photodetectors,and thermoelectric devices. Controlling the carrier polarity and electricalcontact Schottky barriers is of great significance for realizing high-performancePdSe(2) optoelectronic devices. Here, by combining work-functionmeasurement and electrical transport, we observe a thickness-modulatedcarrier polarity transition in layered PdSe2 FETs fromn-type unipolar to intrinsic ambipolar and p-type unipolar behaviorby simply varying the number of layers of PdSe2. Due tothe weak Fermi-level pinning in few-layer PdSe2, n-typeand ambipolar FETs are achieved by contacting PdSe2 toSc, Ti, and Pd electrodes, respectively. The Schottky barrier heightsare determined by temperature-dependent transport, showing a 15 meVbarrier for the Sc contact at the electron side and 62 and 93 meVbarriers for Ti and Pd contacts, both at the hole side, respectively.We further demonstrate ozone-treatment-induced hole doping in PdSe2, which effectively converts the PdSe2 FETs fromn-type to p-type. The doping is robust in the ambient environmentover 3 months. In-plane homojunction on a PdSe2 flake isrealized by selective ozone doping, demonstrating typical diode rectifyingbehavior. The ability to control the carrier polarity and Schottkybarriers in layered PdSe2 makes this 2D semiconductor highlyfeasible for complementary metal-oxide semiconductor device integrationand high-performance photodetectors based on atomically thin p-njunctions.