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We present a Ge/MoS2 van der Waals heterojunction photodetector with a short active region constructed using a transfer process. The device exhibits broadband, self-powered, superior device performance within the visible to infrared wavelength (500–1700 nm) operated in a photovoltaic mode. Intriguingly, a sharp increased gain of 10 556 (93) with a varied breakdown voltage of −8.02 V (−6.25 V) under the 700 nm (1550 nm) laser illumination was observed, which was interpreted as the synergistic effect of both soft and avalanche breakdown behavior. These results imply disposable high-sensitivity broadband light-detection potentials with a simple Ge/MoS2 heterojunction, exempting it from the complex and strict construction requirement of conventional avalanche photodetectors. [ABSTRACT FROM AUTHOR]

We demonstrated that ternary HfAlO2 amorphous film prepared with common co-sputtering technology can be a suitable gate dielectric for bilayer MoTe2 transistors. The film quality can be improved by optimizing the sputtering process and post-annealing treatment, which is superior to its binary Al2O3 and HfO2 components and satisfies gate dielectric criteria. The bilayer MoTe2 transistors with ∼29-nm-thick HfAlO2 gate dielectric exhibit an Ion/Ioff ratio of over 108 by a low operating voltage, together with a small subthreshold swing ≈ 71.22 mV/dec. These promising characteristics favor the development of high-performance and low-power ultrathin MoTe2-based beyond-silicon electronics. [ABSTRACT FROM AUTHOR]

We demonstrated that the carrier polarity of MoTe2 transistors can be modulated by controlling the channel thickness with NiTe2 semimetal contacts. The multilayer MoTe2 transistors (thickness >7.1 nm) exhibit a symmetric ambipolar conduction, and a transition to unipolar p-type polarity occurs as the channel thickness decreased down to ∼2.3 nm. The position of the semimetal NiTe2 work function was verified to be located at the mid-gap of multilayer MoTe2, and the observed transition was interpreted by a synergistic effect of the channel thickness-dependent band alignment and charge transfer behavior with unique NiTe2 semimetal contacts. [ABSTRACT FROM AUTHOR]

A spin-valve heterojunction plays a vital role in many technologies such as non-volatile magnetic random-access memories (MRAMs) and high-density magnetic recording. In particular, a spin-valve device based on two-dimensional van der Waals (vdW) heterostructures offers an excellent route for low power consumption and miniaturization of spintronic devices. However, the Curie temperature (TC) of 2D vdW ferromagnetic crystals is mostly lower than room temperature, and the spin-valve heterostructures of room-temperature ferromagnetic 2D crystals are rare. It is necessary and very challenging to realize the room-temperature spin-valve heterojunctions of 2D ferromagnetic crystals. We prepare a 2D room-temperature, ferromagnetic crystal based 2D vdW Fe3GaTe2/MoSe2/Fe3GaTe2 ferromagnet/semiconductor 2D van der Waals heterojunction. The magnetoresistance (MR) of this heterojunction device reaches 3.7% at room temperature (T = 300 K) and 37.7% at 2 K. Importantly the spin-valve effect can still operate at bias currents as low as 10 nA at room temperature in the ferromagnet/semiconductor 2D van der Waals heterojunction. We open a realistic path to 2D magnetic tunnel junctions for next generation spintronic applications at room temperature. [ABSTRACT FROM AUTHOR]

The discovery of two-dimensional (2D) van der Waals (vdW) ferromagnets has provided a broad platform for the study of spintronics and many novel physical phenomena. However, vdW ferromagnetic crystals generally have a low Curie temperature and poor air stability and their magnetic properties are difficult to modulate. As a layered Dirac semimetal, NiTe2 has excellent properties such as high electrical conductivity and high air stability. In this work, we report for the first time the introduction of ferromagnetism into NiTe2 single crystals by doping Cr atoms with the Te-flux method. By controlling the Cr content, the Curie temperature can be tuned from 210 K to 248 K and the saturation magnetic moment from 1.54 emu g−1 to 2.27 emu g−1 which is much higher than the defective magnetism caused by doping. The doped nanosheets still have extremely high air stability, in contrast with most vdW 2D ferromagnet crystals. The results provide opportunities for the study of new highly-tunable, air-stable vdW ferromagnets and their potential applications. [ABSTRACT FROM AUTHOR]

We demonstrated that Schottky barrier height (SBH) at the metal/CVD-grown MoTe2 interface can be significantly reduced with tunnel contact by inserting a thin Al2O3 layer regardless of the metal work function. The existence of strong Fermi level pinning (FLP) at the metal/MoTe2 interface was verified, while depinning cannot be achieved with Al2O3 insertion. Thus, the fixed charges inside the Al2O3 were proposed to be responsible for the effective SBH reduction in virtue of the eliminated SBH reduction after the post-annealing treatment. This work provides a feasible way to solve the contact issue and favors for the fabrication of high performance MoTe2-based electronic devices. [ABSTRACT FROM AUTHOR]

Recent investigations reveal elemental semimetal (Bi and Sb) contacts fabricated with conventional deposition processes exhibit a remarkable capacity of approaching the quantum limit in two-dimensional (2D) semiconductor contacts, implying it might be an optimal option to solve the contact issue of 2D semiconductor electronics. Here, we demonstrate novel compound Dirac semimetal ZrTe 2 contacts to MoS 2 constructed by a nondestructive van der Waals (vdW) transfer process, exhibiting excellent ohmic contact characteristics with a negligible Schottky barrier. The band hybridization between ZrTe 2 and MoS 2 was verified. The bilayer MoS 2 transistor with a 250 nm channel length on a 20 nm thick hexagonal boron nitride (h-BN) exhibits an I ON / I OFF current ratio over 10 5 and an on-state current of 259 μA μm -1 . The current results reveal that 2D compound semimetals with vdW contacts can offer a diverse selection of proper semimetals with adjustable work functions for the next-generation 2D-based beyond-silicon electronics.