Dataset Information

Layer-by-layer epitaxy of multi-layer MoS₂ wafers.

ABSTRACT: The 2D semiconductor of MoS₂ has great potential for advanced electronics technologies beyond silicon. So far, high-quality monolayer MoS₂ wafers have been available and various demonstrations from individual transistors to integrated circuits have also been shown. In addition to the monolayer, multilayers have narrower band gaps but improved carrier mobilities and current capacities over the monolayer. However, achieving high-quality multi-layer MoS₂ wafers remains a challenge. Here we report the growth of high-quality multi-layer MoS₂ 4-inch wafers via the layer-by-layer epitaxy process. The epitaxy leads to well-defined stacking orders between adjacent epitaxial layers and offers a delicate control of layer numbers up to six. Systematic evaluations on the atomic structures and electronic properties were carried out for achieved wafers with different layer numbers. Significant improvements in device performances were found in thicker-layer field-effect transistors (FETs), as expected. For example, the average field-effect mobility (μ _FE) at room temperature (RT) can increase from ∼80 cm²·V^-1·s^-1 for monolayers to ∼110/145 cm²·V^-1·s^-1 for bilayer/trilayer devices. The highest RT μ _FE of 234.7 cm²·V^-1·s^-1 and record-high on-current densities of 1.70 mA·μm^-1 at V _ds = 2 V were also achieved in trilayer MoS₂ FETs with a high on/off ratio of >10⁷. Our work hence moves a step closer to practical applications of 2D MoS₂ in electronics.

SUBMITTER: Wang Q

PROVIDER: S-EPMC9232293 | biostudies-literature | 2022 Jun

REPOSITORIES: biostudies-literature

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Publications

Layer-by-layer epitaxy of multi-layer MoS2 wafers.

Wang Qinqin Q Tang Jian J Li Xiaomei X Tian Jinpeng J Liang Jing J Li Na N Ji Depeng D Xian Lede L Guo Yutuo Y Li Lu L Zhang Qinghua Q Chu Yanbang Y Wei Zheng Z Zhao Yanchong Y Du Luojun L Yu Hua H Bai Xuedong X Gu Lin L Liu Kaihui K Yang Wei W Yang Rong R Shi Dongxia D Zhang Guangyu G

National science review 20220421 6

The 2D semiconductor of MoS2 has great potential for advanced electronics technologies beyond silicon. So far, high-quality monolayer MoS2 wafers have been available and various demonstrations from individual transistors to integrated circuits have also been shown. In addition to the monolayer, multilayers have narrower band gaps but improved carrier mobilities and current capacities over the monolayer. However, achieving high-quality multi-layer MoS2 wafers rema ...[more]

PMID: 35769232

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Project description:Two-dimensional (2D) layered materials offer unique properties that make them attractive for continued scaling in electronic and optoelectronic device applications. Successful integration of 2D materials into semiconductor manufacturing requires high-volume and high-precision processes for deposition and etching. Several promising large-scale deposition approaches have been reported for a range of 2D materials, but fewer studies have reported removal processes. Thermal atomic layer etching (ALE) is a scalable processing technique that offers precise control over isotropic material removal. In this work, we report a thermal ALE process for molybdenum disulfide (MoS2). We show that MoF6 can be used as a fluorination source, which, when combined with alternating exposures of H2O, etches both amorphous and crystalline MoS2 films deposited by atomic layer deposition. To characterize the ALE process and understand the etching reaction mechanism, in situ quartz crystal microbalance (QCM), Fourier transform infrared (FTIR), and quadrupole mass spectrometry (QMS) experiments were performed. From temperature-dependent in situ QCM experiments, the mass change per cycle was -5.7 ng/cm2 at 150 °C and reached -270.6 ng/cm2 at 300 °C, nearly 50× greater. The temperature dependence followed Arrhenius behavior with an activation energy of 13 ± 1 kcal/mol. At 200 °C, QCM revealed a mass gain following exposure to MoF6 and a net mass loss after exposure to H2O. FTIR revealed the consumption of Mo-O species and formation of Mo-F and MoF x =O species following exposures of MoF6 and the reverse behavior following H2O exposures. QMS measurements, combined with thermodynamic calculations, supported the removal of Mo and S through the formation of volatile MoF2O2 and H2S byproducts. The proposed etching mechanism involves a two-stage oxidation of Mo through the ALE half-reactions. Etch rates of 0.5 Å/cycle for amorphous films and 0.2 Å/cycle for annealed films were measured by ex situ ellipsometry, X-ray reflectivity, and transmission electron microscopy. Precisely etching amorphous films and subsequently annealing them yielded crystalline, few-layer MoS2 thin films. This thermal MoS2 ALE process provides a new mechanism for fluorination-based ALE and offers a low-temperature approach for integrating amorphous and crystalline 2D MoS2 films into high-volume device manufacturing with tight thermal budgets.

Dataset Information

Layer-by-layer epitaxy of multi-layer MoS₂ wafers.

Publications

Layer-by-layer epitaxy of multi-layer MoS<sub>2</sub> wafers.

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