The extraordinary properties of two dimensional (2D) materials, such as the extremely high carrier mobility 1,2 in graphene and the large direct band gaps in transition metal dichalcogenides MX 2 (M = Mo or W, X = S, Se) monolayers 3 , highlight the crucial role quantum confinement can have in producing a wide spectrum of technologically important electronic properties. Currently one of the highest priorities in the field is to search for new 2D crystalline systems with structural and electronic properties that can be exploited for device development. In this letter, we report on the unusual quantum transport properties of the 2D ternary transition

1 of 7) 1606469 electrical and optical properties. [1][2][3][4] Unlike graphene with zero bandgap, transition metal dichalcogenides (TMDs) such as MoS 2 and WS 2 show bandgaplayer-dependent properties, e.g., bulk or multilayer MoS 2 is a semiconductor with an indirect bandgap of 1.2 eV, while single-layer MoS 2 shows a direct bandgap of 1.8 eV. Among TMD family members, MoS 2 -and WS 2 -based field effect transistors (FETs) have been intensively studied in the research community over the years. MoS 2 -or WS 2 -based FETs with excellent electrical characteristics have been demonstrated, such as high current on/ off ratio (10 6 -10 8 ), low subthreshold swing (≈70-80 mV per decade), and mobility up to ≈140-200 cm 2 V −1 s −1 (in highk/MoS 2 /high-k structure). [5][6][7] These results demonstrate a bright future for the applications of TMDs in electronics and optoelectronics. In order to fully harvest the 2D materials for the applications, sizable and tunable bandgap is essential. Although as-existing TMD family members have such bandgap selectivity separately, such as WS 2 ≈ 2.0 eV, WSe 2 ≈ 1.65 eV, MoS 2 ≈ 1.8 eV, and MoSe 2 ≈ 1.55 eV, [8][9][10] along with efforts in the yield of the bandgap tuning by strain, electrical gating, etc., [11][12][13][14] systematical engineering in bandgap in the distinct development of an intact material system is still very important in the real commercialization of 2D materials. Alloying is a good protocol to realize the tunability of bandgap in one material system. Boron nitride was reported to become alloyed into graphene in order to tune the bandgap of the mixed graphene materials, but it resulted in isolated domains in two kinds of phases due to the immiscible nature of each one. [15,16] Owing to the similarity in structure of TMD family members, ternary or even quaternary material systems are very promising. Depending on the density functional theory (DFT) calculation, ternary 2D alloys show better thermal stability than those of pure binary materials, due to lower internal mixing energy. [17] Recently, W x Mo 1−x S 2 [18][19][20][21] and MoS 2(1−x) Se 2x [22] are successfully synthesized by chemical vapor deposition (CVD) techniques. However, the alloying quality of these ternary materials is still limited in the status of mixed phases of WS 2 and MoS 2 , far from the intact ternary system, hence in the absence of predominant investigation of electronic properties based on their field effect transistors.Monolayer W x Mo 1−x S 2 -based field effect transistors are demonstrated for the first time on the monolayer W x Mo 1−x S 2 flake, which is grown by the chemical vapor deposition method under an atmospheric pressure. Detailed material studies using Raman and photoluminescence measurements have been carried out on the as-grown monolayer W x Mo 1−x S 2 . Electronic band structure of monolayer W x Mo 1−x S 2 has been calculated using first-principle theory. The thermal stability of monolayer W x Mo 1−x S 2 has been evaluated using Raman-temperature measurement. Carrier transpor...

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The energy band alignment between HfO2/multilayer (ML)-MoS2 was characterized using high-resolution x-ray photoelectron spectroscopy. The HfO2 was deposited using an atomic layer deposition tool, and ML-MoS2 was grown by chemical vapor deposition. A valence band offset (VBO) of 1.98 eV and a conduction band offset (CBO) of 2.72 eV were obtained for the HfO2/ML-MoS2 interface without any treatment. With CHF3 plasma treatment, a VBO and a CBO across the HfO2/ML-MoS2 interface were found to be 2.47 eV and 2.23 eV, respectively. The band alignment difference is believed to be dominated by the down-shift in the core level of Hf 4d and up-shift in the core level of Mo 3d, or the interface dipoles, which caused by the interfacial layer in rich of F.

Black phosphorus (BP) has emerged as a promising two-dimensional (2D) material for next generation transistor applications due to its superior carrier transport properties. Among other issues, achieving reduced subthreshold swing and enhanced hole mobility simultaneously remains a challenge which requires careful optimization of the BP/gate oxide interface. Here, we report the realization of high performance BP transistors integrated with HfO2 high-k gate dielectric using a low temperature CMOS process. The fabricated devices were shown to demonstrate a near ideal subthreshold swing (SS) of ~69 mV/dec and a room temperature hole mobility of exceeding >400 cm2/Vs. These figure-of-merits are benchmarked to be the best-of-its-kind, which outperform previously reported BP transistors realized on traditional SiO2 gate dielectric. X-ray photoelectron spectroscopy (XPS) analysis further reveals the evidence of a more chemically stable BP when formed on HfO2 high-k as opposed to SiO2, which gives rise to a better interface quality that accounts for the SS and hole mobility improvement. These results unveil the potential of black phosphorus as an emerging channel material for future nanoelectronic device applications.