Mo-based van der Waals heterojunction p-n diodes with p-type α-MoTe2 and n-type MoS2 are fabricated on glass, and demonstrate excellent static and dynamic device performances at a low voltage of 5 V, with an ON/OFF current ratio higher than 10(3) , ideality factors of 1.06, dynamic rectification at a high frequency of 1 kHz, high photoresponsivity of 322 mA W(-1) , and an external quantum efficiency of 85% under blue-light illumination.

Two-dimensional (2D) molybdenum disulfide (MoS₂) field-effect transistors (FETs) have been extensively studied, but most of the FETs with gate insulators have displayed negative threshold voltage values, which indicates the presence of interfacial traps both shallow and deep in energy level. Despite such interface trap issues, reports on trap densities in MoS₂ are quite limited. Here, we probed top-gate MoS₂ FETs with two- (2L), three- (3L), and four-layer (4L) MoS₂/dielectric interfaces to quantify deep-level interface trap densities by photo-excited charge collection spectroscopy (PECCS), and reported the result that deep-level trap densities over 10(12) cm(-2) may exist in the interface and bulk MoS₂ near the interface. Transfer curve hysteresis and PECCS measurements show that shallow traps and deep traps are not that different in density order from each other. We conclude that our PECCS analysis distinguishably provides valuable information on deep level interface/bulk trap densities in 2D-based FETs.

Two-dimensional (2D) semiconductor materials with discrete bandgap become important because of their interesting physical properties and potentials toward future nanoscale electronics. Many 2D-based field effect transistors (FETs) have thus been reported. Several attempts to fabricate 2D complementary (CMOS) logic inverters have been made too. However, those CMOS devices seldom showed the most important advantage of typical CMOS: low power consumption. Here, we adopted p-WSe2 and n-MoS2 nanosheets separately for the channels of bottom-gate-patterned FETs, to fabricate 2D dichalcogenide-based hetero-CMOS inverters on the same glass substrate. Our hetero-CMOS inverters with electrically isolated FETs demonstrate novel and superior device performances of a maximum voltage gain as ∼27, sub-nanowatt power consumption, almost ideal noise margin approaching 0.5VDD (supply voltage, VDD=5 V) with a transition voltage of 2.3 V, and ∼800 μs for switching delay. Moreover, our glass-substrate CMOS device nicely performed digital logic (NOT, OR, and AND) and push-pull circuits for organic light-emitting diode switching, directly displaying the prospective of practical applications.

Molybdenum ditelluride (α-MoTe2) is an emerging transition-metal dichalcogenide (TMD) semiconductor that has been attracting attention due to its favorable optical and electronic properties. Field-effect transistors (FETs) based on few-layer α-MoTe2 nanosheets have previously shown ambipolar behavior with strong p-type and weak n-type conduction. We have employed a direct imprinting technique following mechanical nanosheet exfoliation to fabricate high-performance complementary inverters using α-MoTe2 as the semiconductor for the p-channel FETs and MoS2 as the semiconductor for the n-channel FETs. To avoid ambipolar behavior and produce α-MoTe2 FETs with clean p-channel characteristics, we have employed the high-workfunction metal platinum for the source and drain contacts. As a result, our α-MoTe2 nanosheet p-channel FETs show hole mobilities up to 20 cm(2)/(V s), on/off ratios up to 10(5), and a subthreshold slope of 255 mV/decade. For our complementary inverters composed of few-layer α-MoTe2 p-channel FETs and MoS2 n-channel FETs we have obtained voltage gains as high as 33, noise margins as high as 0.38 VDD, a switching delay of 25 μs, and a static power consumption of a few nanowatts.

Recently, α-MoTe , a 2D transition-metal dichalcogenide (TMD), has shown outstanding properties, aiming at future electronic devices. Such TMD structures without surface dangling bonds make the 2D α-MoTe a more favorable candidate than conventional 3D Si on the scale of a few nanometers. The bandgap of thin α-MoTe appears close to that of Si and is quite smaller than those of other typical TMD semiconductors. Even though there have been a few attempts to control the charge-carrier polarity of MoTe , functional devices such as p-n junction or complementary metal-oxide-semiconductor (CMOS) inverters have not been reported. Here, we demonstrate a 2D CMOS inverter and p-n junction diode in a single α-MoTe nanosheet by a straightforward selective doping technique. In a single α-MoTe flake, an initially p-doped channel is selectively converted to an n-doped region with high electron mobility of 18 cm V s by atomic-layer-deposition-induced H-doping. The ultrathin CMOS inverter exhibits a high DC voltage gain of 29, an AC gain of 18 at 1 kHz, and a low static power consumption of a few nanowatts. The results show a great potential of α-MoTe for future electronic devices based on 2D semiconducting materials.

3146 wileyonlinelibrary.com disulfi de (MoS 2 ) and tungsten dislenide (WSe 2 ) are typesetting materials showing n-and p-type dominant conductions, respectively. [7][8][9][10][11] As one of quite recent 2D TMD materials, molybdenum ditelluride (α-MoTe 2 ) has also been attracting attention due to its optical and electrical properties. Monolayer α-MoTe 2 exhibits a direct optical bandgap of 1.10 eV, while its bulk form becomes an indirect semiconductor with the band gap of 0.85-1.0 eV. [12][13][14] Interestingly, it is reported that MoTe 2 shows structural and electronic phase transition. The structural phase transition from hexagonal (2H) phase to monoclinic (distorted octahedral or 1T) phase is reversible at a high temperature. [ 15 ] According to literatures, [16][17][18][19][20] few-layered α-MoTe 2 fi eld effect transistors (FETs) showed ambipolar type conduction with broad range of mobilities in 0.2-30 cm 2 V −1 s −1 for both electrons and holes, depending on the source/drain (S/D) contact electrodes, gate dielectrics, and their process conditions. Contact resistance and dielectric/ MoTe 2 channel interface are certainly affecting factors for the electrical performances of a few-layer α-MoTe 2 FETs.In the present work, we have fabricated all-2D α-MoTe 2 -based FETs on glass, using a few tens nm-thin hexagonal boron nitride (h-BN) and a few layer-thin graphene in consideration of good dielectric/channel interface and S/D contacts, respectively. Very few but similar attempts for all 2D FETs were conducted with MoS 2 and WSe 2 nanosheets. [ 21,22 ] Here, distinguished from previous works, our all-2D FETs with α-MoTe 2 nanofl akes are dual-gated for driving higher current, using two h-BN layers for top and bottom dielectrics. Moreover, for our 2D dual gate FET fabrications on glass, all thermal annealing and lithography processes were intentionally exempted. This means that our dual gate 2D FETs may be formed in a fully non-lithographic method by using only van der Waal's forces. Our dual-gate α-MoTe 2 FET displays quite a high hole and electron mobility over ≈20 cm 2 V −1 s −1 along with ON/OFF ratio of ≈10 5 in maximum as an ambipolar FET and also demonstrates drain current as high as a few tens-to-hundred µA at a low drain voltage of −2 V, which appears enough to switch organic light emitting diodes (OLEDs) for blue light. Non-Lithographic Fabrication of All-2D α-MoTe 2 Dual Gate TransistorsKyunghee Choi , Young Tack Lee , Jin Sung Kim , Sung-Wook Min , Youngsuk Cho , Atiye Pezeshki , Do Kyung Hwang , * and Seongil Im * As one of the emerging new transition-metal dichalcogenides materials, molybdenum ditelluride (α-MoTe 2 ) is attracting much attention due to its optical and electrical properties. This study fabricates all-2D MoTe 2 -based fi eld effect transistors (FETs) on glass, using thin hexagonal boron nitride and thin graphene in consideration of good dielectric/channel interface and source/drain contacts, respectively. Distinguished from previous works, in this study, all 2D FETs with α-MoTe 2 na...

High‐performance, air‐stable, p‐channel WSe2 top‐gate field‐effect transistors (FETs) using a bilayer gate dielectric composed of high‐ and low‐k dielectrics are reported. Using only a high‐k Al2O3 as the top‐gate dielectric generally degrades the electrical properties of p‐channel WSe2, therefore, a thin fluoropolymer (Cytop) as a buffer layer to protect the 2D channel from high‐k oxide forming is deposited. As a result, a top‐gate‐patterned 2D WSe2 FET is realized. The top‐gate p‐channel WSe2 FET demonstrates a high hole mobility of 100 cm2­ V−1 s−1 and a ION/IOFF ratio > 107 at low gate voltages (VGS ca. −4 V) and a drain voltage (VDS) of −1 V on a glass substrate. Furthermore, the top‐gate FET shows a very good stability in ambient air with a relative humidity of 45% for 7 days after device fabrication. Our approach of creating a high‐k oxide/low‐k organic bilayer dielectric is advantageous over single‐layer high‐k dielectrics for top‐gate p‐channel WSe2 FETs, which will lead the way toward future electronic nanodevices and their integration.

A 1D-2D hybrid complementary logic inverter comprising of ZnO nanowire and WSe2 nanosheet field-effect transistors (FETs) is fabricated on glass, which shows excellent static and dynamic electrical performances with a voltage gain of ≈60, sub-nanowatt power consumption, and at least 1 kHz inverting speed.