Chemically Tuned p‐ and n‐Type WSe₂ Monolayers with High Carrier Mobility for Advanced Electronics

Abstract

Monolayers of transition metal dichalcogenides (TMDCs) have attracted a great interest for post‐silicon electronics and photonics due to their high carrier mobility, tunable bandgap, and atom‐thick 2D structure. With the analogy to conventional silicon electronics, establishing a method to convert TMDC to p‐ and n‐type semiconductors is essential for various device applications, such as complementary metal‐oxide‐semiconductor (CMOS) circuits and photovoltaics. Here, a successful control of the electrical polarity of monolayer WSe2 is demonstrated by chemical doping. Two different molecules, 4‐nitrobenzenediazonium tetrafluoroborate and diethylenetriamine, are utilized to convert ambipolar WSe2 field‐effect transistors (FETs) to p‐ and n‐type, respectively. Moreover, the chemically doped WSe2 show increased effective carrier mobilities of 82 and 25 cm2 V−1s−1 for holes and electrons, respectively, which are much higher than those of the pristine WSe2. The doping effects are studied by photoluminescence, Raman, X‐ray photoelectron spectroscopy, and density functional theory. Chemically tuned WSe2 FETs are integrated into CMOS inverters, exhibiting extremely low power consumption (≈0.17 nW). Furthermore, a p‐n junction within single WSe2 grain is realized via spatially controlled chemical doping. The chemical doping method for controlling the transport properties of WSe2 will contribute to the development of TMDC‐based advanced electronics.

Low‐Power Complementary Inverter with Negative Capacitance 2D Semiconductor Transistors

“…As the thickness of the dielectric and the channel of FETs is approaching a few nanometers, electrostatic gate control of nanoscale FETs becomes ineffective, giving rise to the increase of the subthreshold slope (SS) and leakage current and undesirable excessive power dissipation. [ 6–11 ] It is essential to reduce the SS and achieve efficient gate control of the channel for realizing low‐power electronic devices. However, the SS of FET is limited by the Boltzmann distribution from reaching 60 mV dec −1 at room temperature, and therefore precludes the reduction of the supply voltage and the overall power consumption.…”

“…CMOS logic dissipates less static power than transistor‐transistor logic or NMOS logic because of the low static current, and is one of the most used technologies in VLSI chips. [ 5,8,19–21 ] The construction of complementary circuits requires both n‐ and p‐type unipolar FETs. However, most of TMD semiconductors (MoS 2 , WS 2 , etc.)…”

“…[ 21–28 ] Even for tungsten diselenide (WSe 2 ) with balanced conduction and valence band edges, it usually exhibits ambipolar transport characteristics without doping. [ 2,5,8,29 ] Thus, it is of great importance to fabricate unipolar p‐type TMD semiconductors FETs to achieve complementary NCFET in a controllable manner. At the same time, the switching behavior mainly occurs at the subthreshold region.…”

Ambipolar 2D Semiconductors and Emerging Device Applications

“…Lim et al obtained MoTe 2 CMOS inverters with a high DC voltage gain of 29 and an AC voltage gain of ≈18 at 1 kHz, where the P-FET was realized with Pt electrical contact and the N-FET was of Ti/Au contact and ALD-driven Al 2 O 3 H-dopants. [261] Recently, Park et al proposed a prototype homogeneous CMOS PMMA, [221] BV, [222] Cs 2 CO 3 , [255] K, [263] Si x N y [264] Contact Pd [45,109] Ti, [45] Ni [109] MoS 2 Dopant Nb,* [212] P,* [215] AuCl 3 [217,218] BV, [218] K [256] Contact Pt(transferred), [123] Au, [126] Pd [126,160] Mo, [114] Sc, [114] Ti [161] MoSe 2 Dopant Nb* [213] -Contact --WSe 2 Dopant NO 2 , [185] 4-NBD, [253] MoO 3 , [258] F 4 TCNQ-PMMA [260] CTAB, [219] DETA, [253] K, [256,257] AlO x [260] Contact Pd [44,185] Ni, [44] Ag, [183] Ti [185] MoTe 2 Dopant -BV, [254] Al 2 O 3 inverter by depositing Al 2 O 3 film on the CVD-MoTe 2 to convert it from P-type to N-type, offering a possibility for future large scale CMOS circuit applications. [259] BP is expected to be a good candidate for electronic circuits owning to its tunable direct bandgap and high carrier mobility, which is recognized as an ambipolar s...…”

Reconfigurable Multifunctional Ambipolar Polymer Transistors with Improved Switching-off Capability Upon Non-Uniformly Distributed Compensation Potential

“…Several methods aiming at either modifying the ambipolar materials or optimizing the device structures were proposed to promote the applications of ambipolar materials for high performance transistors and CMOS-like circuits, and among them are two representative examples: 1) Converting ambipolar to unipolar (p-type or n-type) during device fabrication or post-processing to improve the off-state. Particularly, contact engineering, chemical doping and modification of dielectrics are adopted to suppress the ambipolar transport [25][26][27][28][29][30][31] , which sacrifice the multifunctional operation characteristics of ambipolar transistors. 2) Suppressing the injection and accumulation of electrons (holes) from the drain electrodes in p-type (n-type) working mode through modified device construction and additional control signals to gain a high on/off ratio.…”