High Mobility 2D Palladium Diselenide Field‐Effect Transistors with Tunable Ambipolar Characteristics

Abstract

Due to the intriguing optical and electronic properties, 2D materials have attracted a lot of interest for the electronic and optoelectronic applications. Identifying new promising 2D materials will be rewarding toward the development of next generation 2D electronics. Here, palladium diselenide (PdSe ), a noble-transition metal dichalcogenide (TMDC), is introduced as a promising high mobility 2D material into the fast growing 2D community. Field-effect transistors (FETs) based on ultrathin PdSe show intrinsic ambipolar characteristic. The polarity of the FET can be tuned. After vacuum annealing, the authors find PdSe to exhibit electron-dominated transport with high mobility (µ = 216 cm V s ) and on/off ratio up to 10 . Hole-dominated-transport PdSe can be obtained by molecular doping using F -TCNQ. This pioneer work on PdSe will spark interests in the less explored regime of noble-TMDCs.

Anisotropic Growth and Scanning Tunneling Microscopy Identification of Ultrathin Even‐Layered PdSe2 Ribbons

“…By virtue of the thickness variable feature, Raman measurements were also performed on the transferred PdSe 2 flakes on SiO 2 /Si to establish a one‐to‐one correspondence between thickness and Raman modes. As displayed in Figure e, three notable peaks (at ≈143.2, ≈221.8, and ≈256.1 cm −1 ) are identified as the fingerprints of bulk PdSe 2 , the same as those of the mechanically exfoliated samples . Notably, with the thickness reducing to 2L, the three vibrational modes are shifted to higher frequencies (A g 1 : ≈152.5 cm −1 ; B 1g 2 : ≈229.6 cm −1 ; A g 3 : ≈264.9 cm −1 ), showing remarkable shifts by ≈9.3, ≈7.8, and ≈8.8 cm −1 , respectively.…”

“…Raman spectroscopy was further utilized to determine the formation and air stability of PdSe 2 on Au foils (Figure f). For the freshly grown PdSe 2 sample, the Raman peaks at ≈149.5 and ≈228.1 cm −1 are attributed to A g 1 and B 1g 2 vibrational modes, relating to the movements of Se atoms, while the peak at ≈263.1 cm −1 is assigned to the A g 3 vibrational mode, due to the relative movements between Se and Pd atoms . In contrast to bulk PdSe 2 , a new peak appears at ≈124.2 cm −1 , which is explained to arise from the variation of space group from bulk to few‐layer (from Pbca to Pca2 1 ) .…”

“…Until now, most reported monolayer or few‐layer PdSe 2 samples have been achieved by mechanical exfoliation, molecular beam epitaxy (MBE), and selenization of predeposited Pd layers . Low productivity, high cost, small domain size, and uncontrolled layer thickness were usually resulted, strongly hindering the practical applications of PdSe 2 in related fields.…”

The ambipolar transport behavior of WSe2 transistors and its analogue circuits

“…To evaluate the Schottky barrier height between metal and WSe 2 , I DS could be defined by 2D thermionic emission (Eq. (5)) due to its sufficiently thin channel 41 .…”

“…Figure 3e shows the effective Schottky barrier as a function of the gate voltage of 1L, 7L, and 12L WSe 2 devices. A peak between −10 and 0 V in the 7L WSe 2 device is attributed to the opposite polarities of Schottky contact, which could be tuned based upon the gate voltage 41 . As seen, the effective Schottky barrier for the hole carrier is strongly dependent on the gate voltage compared to that for the electron carrier.…”