2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

Abstract

2D layered materials (2DLMs) have come under the limelight of scientific and engineering research and broke new ground across a broad range of disciplines in the past decade. Nevertheless, the members of stoichiometric 2DLMs are relatively limited. This renders them incompetent to fulfill the multitudinous scenarios across the breadth of electronic and optoelectronic applications since the characteristics exhibited by a specific material are relatively monotonous and limited. Inspiringly, alloying of 2DLMs can markedly broaden the 2D family through composition modulation and it has ushered a whole new research domain: 2DLM alloy nano-electronics and nano-optoelectronics. This review begins with a comprehensive survey on synthetic technologies for the production of 2DLM alloys, which include chemical vapor transport, chemical vapor deposition, pulsed-laser deposition, and molecular beam epitaxy, spanning their development, as well as, advantages and disadvantages. Then, the up-to-date advances of 2DLM alloys in electronic devices are summarized. Subsequently, the up-to-date advances of 2DLM alloys in optoelectronic devices are summarized. In the end, the ongoing challenges of this emerging field are highlighted and the future opportunities are envisioned, which aim to navigate the coming exploration and fully exert the pivotal role of 2DLMs toward the next generation of electronic and optoelectronic devices.

Keywords: 2D layered material alloys; alloy engineering; electronic devices; optoelectronic devices.

Figure 1

CVT growth of 2DLM alloys. a) Schematic diagram of the typical experimental setup of CVT growth of layered material alloys and the affecting factors. b) Raman spectra of the CVT‐grown Mo_{1− x} W _x S₂ alloys with different compositions.^{[ 126 ]} Reproduced with permission.^{[ 126 ]} Copyright 2014, Royal Society of Chemistry. c) Selected area electron diffraction pattern, d) high‐resolution transmission electron microscope image and e) element mapping images of the CVT‐grown Nb_{1− x} Ti _x S₃ alloy.^{[ 125 ]} c–e) Reproduced with permission.^{[ 125 ]} Copyright 2020, John Wiley and Sons, Inc. f) Schematic illustration of two routes for producing 2DLMs via CVT. g) An optical microscope image of the as‐grown few‐layer Mo _x W_{1− x} S₂.^{[ 127 ]} f–g) Reproduced with permission.^{[ 127 ]} Copyright 2017, John Wiley and Sons, Inc.

Figure 2

CVD growth of 2DLM alloys. a) Schematic diagram of the CVD growth of 2D MoS_{2(1− x )}Se_{2 x} alloy.^{[ 130 ]} Reproduced with permission.^{[ 130 ]} Copyright 2017, Royal Society of Chemistry. b) Schematic illustration of the mechanism for a two‐step CVD growth of 2D Sn _x W_{1− x} S₂ alloy.^{[ 132 ]} Reproduced with permission.^{[ 132 ]} Copyright 2019, American Chemical Society. c) Schematic illustration of a two‐step synthesis procedure of 2D Mo_{1− x} W _x S₂ alloy.^{[ 133 ]} Reproduced with permission.^{[ 133 ]} Copyright 2018, American Chemical Society.

Figure 3

PLD growth of 2DLM alloys. a) Digital photograph of the PLD‐grown Mo_0.5W_0.5S₂ alloy on a SiO₂/Si substrate. b) X‐ray diffraction pattern. The inset shows the schematic diagrams of the crystal structure.^{[ 155 ]} a–b) Reproduced with permission.^{[ 155 ]} Copyright 2016, American Chemical Society. c,d) Digital photographs of the PLD‐grown Mo_0.5W_0.5S₂ alloy on polyimide and sapphire substrates.^{[ 156 ]} c,d) Reproduced with permission.^{[ 156 ]} Copyright 2017, American Chemical Society.

Figure 4

MBE growth of 2DLM alloys. a) Schematic diagram of a typical MBE growth system. b) High‐resolution scanning transmission electron microscope image of the MBE‐grown 2D (Bi_{1− x} Sb _x )₂Se₃ alloy. The top and bottom insets show the corresponding selected area electron diffraction patterns from the (Bi_{1− x} Sb _x )₂Se₃ and substrate, respectively. c) Angle‐resolved photoemission spectroscopy images of the (Bi_{1− x} Sb _x )₂Se₃ alloys for x = 0 c_a), 0.25 c_b), 0.45 c_c), 0.7 c_d).^{[ 172 ]} b,c) Reproduced with permission.^{[ 172 ]} Copyright 2018, IOP Publishing Ltd.

Figure 5

A schematic summary of the advantages and disadvantages of CVT, CVD, PLD, and MBE.

Figure 6

The application of 2DLM alloys for FETs. a) The periodic table of elements showing the positions of Sn, Pb, Se (left), and the schematic diagram of the crystal structure of Pb _x Sn_{1− x} Se₂ (right). b–e) Transfer curves of the monolayer SnSe₂ and Pb _x Sn_{1− x} Se₂ FETs in linear and logarithmic scale. Source‐drain voltage: 0.25–1 V.^{[ 122 ]} a–e) Reproduced with permission.^{[ 122 ]} Copyright 2018, IOP Publishing Ltd. f) Transfer curves in logarithmic scale of a series of FETs based on monolayer WS_{2 x} Se_{2−2 x} alloys (x = 1, 0.79, 0.66, 0.47, 0.28, and 0, respectively). Source‐drain voltage: 1–3 V.^{[ 180 ]} Reproduced with permission.^{[ 180 ]} Copyright 2020, Royal Society of Chemistry.

Figure 7

The application of 2DLM alloys for diodes. a) Schematic diagram of an InSe/In_0.24Ga_0.76Se diode. b) Transfer curves of In_{1− x} Ga _x Se FETs with different contents of Ga (x = 0, 0.24, 0.76). c) I–V curves of an InSe/In_0.24Ga_0.76Se diode in logarithmic scale (pink) and linear scale (blue).^{[ 192 ]} a–c) Reproduced with permission.^{[ 192 ]} Copyright 2020, American Chemical Society. d,e) Transfer curves of the pristine and oxygen plasma treated MoS₂ FETs. f) Band diagram and density of states of the O₂ ⁺ doped MoS₂. g) Schematic illustration of the fabrication of an in‐plane MoS₂/MoS_{2− x} O _x heterojunction. h) I–V curve of a MoS₂/MoS_{2− x} O _x diode in logarithmic scale (black) and linear scale (blue).^{[ 198 ]} d–h) Reproduced with permission.^{[ 198 ]} Copyright 2019, IOP Publishing Ltd. i) I–V curves of a compositionally graded Mo_{1− x} W _x S₂ diode under various gate voltages. The inset shows the optical microscope image of a typical device. j) Band diagram illustrating the working mechanism. k) Rectification ratio as a function of gate voltage.^{[ 199 ]} i–k) Reproduced with permission.^{[ 199 ]} Copyright 2019, American Chemical Society.

Figure 8

The application of 2DLM alloys for logic inverters. a) Schematic illustration of the alloying induced transition of charge‐carrier polarity. b,c) I–V curves of the MoSe₂ and Nb _x Mo_{1− x} Se₂ FETs under various gate voltages from 0 to 80 V. d) Transfer curves of the MoSe₂ and Nb _x Mo_{1− x} Se₂ FETs. The inset presents the data in logarithmic scale. e) Conversion characteristic of an inverter built of the n‐type MoSe₂ and p‐type Nb _x Mo_{1− x} Se₂ FETs.^{[ 209 ]} Reproduced with permission.^{[ 209 ]} Copyright 2015, John Wiley and Sons, Inc.

Figure 9

Suppression of deep‐level defect states by 2DLM alloy for improved photosensitivity. a) A summary of the responsivity of a PLD‐produced Mo_0.5W_0.5S₂ alloy photodetector and other photodetectors based on binary Mo‐/W‐based dichalcogenides produced by various methods. b) Temporal photoresponse of a PLD‐produced Mo_0.5W_0.5S₂ photodetector. c) Band diagram illustrating the working mechanism of the suppression of deep‐level defect states by alloy engineering.^{[ 155 ]} a–c) Reproduced with permission.^{[ 155 ]} Copyright 2016, American Chemical Society. d) PL intensity of the Mo _x W_{1− x} S₂ alloy as a function of Mo composition.^{[ 230 ]} Reproduced with permission.^{[ 230 ]} Copyright 2018, Nature Publishing Group. e) Band diagrams showing the defect levels of Se vacancy in MoSe₂ (left) and Se vacancy in Mo_0.75W_0.25Se₂ surrounded by Mo atoms (middle) or W atoms (right).^{[ 231 ]} Reproduced with permission.^{[ 231 ]} Copyright 2017, John Wiley and Sons, Inc. f,g) Responsivity and EQE as a function of power density of graphene/InSe_{1− x} S _x (x = 0.1, 0.2, 0.3) heterojunction photodetectors.^{[ 240 ]} f,g) Reproduced with permission.^{[ 240 ]} Copyright 2020, Royal Society of Chemistry.

Figure 10

2DLM alloys for broadband photodetectors. a) Total density of states of the Mo _x Re_{1− x} S₂ alloys with different compositions. b) Photoswitching curves of the ReS₂, MoS₂, and Mo _x Re_{1− x} S₂ photodetectors under 532, 633, 980, and 1550 nm illumination.^{[ 253 ]} a,b) Reproduced with permission.^{[ 253 ]} Copyright 2020, John Wiley and Sons, Inc. c) Absorption spectrum of b‐As_0.83P_0.17. The inset presents a schematic diagram of a b‐As_0.83P_0.17 phototransistor. d) Responsivity (red) and EQE (blue) of a b‐As_0.83P_0.17 photodetector as a function of wavelength.^{[ 259 ]} c,d) Reproduced with permission.^{[ 259 ]} Copyright 2017, American Association for the Advancement of Science.

Figure 11

2DLM alloys for self‐powered photodetectors. a) Transfer curves of a series of InSe_{1− x} Te _x FETs with different contents of Te. The inset presents the schematic diagram of an InSe_{1− x} Te _x FET. b) Schematic illustration of the band alignment of an InSe/InSe_0.82Te_0.18 heterojunction. E _C, E _V, and E _F represent CBM, VBM, and Fermi level, respectively. c) I–V curves of an InSe/InSe_0.82Te_0.18 diode in dark in logarithmic scale (black) and in linear scale (blue). d) I–V curves of an InSe/InSe_0.82Te_0.18 photodetector in dark and under light illumination with wavelengths from 400 to 1100 nm. e) Photoswitching curve under periodic 900 nm light illumination at a self‐powered working mode. f) Temporal photoresponse.^{[ 276 ]} a–f) Reproduced with permission.^{[ 276 ]} Copyright 2020, Elsevier Ltd. g) I–V curves of an InSe/In_0.24Ga_0.76Se heterojunction photodetector in dark and under illumination with wavelengths from 400 to 1000 nm. h) PL spectra of In_{1− x} Ga _x Se with different contents of Ga. i) Photoswtiching curves of an InSe/In_0.24Ga_0.76Se heterojunction photodetector under periodic light illumination with different wavelengths from 400 to 1000 nm.^{[ 192 ]} g–i) Reproduced with permission.^{[ 192 ]} Copyright 2020, American Chemical Society.

Figure 12

Graded 2DLM alloy for improved photosensitivity. a) Schematic diagram of a Mo_{1− x} W _x S₂ alloy photodetector with graded composition distribution. b,c) Responsivity and detectivity as a function of power density of incident light under illumination with different wavelengths. d) Band diagram of a Mo_{1− x} W _x S₂ alloy photodetector with graded composition distribution. E _C, E _V, and E _F represent CBM, VBM, and Fermi level, respectively.^{[ 199 ]} a–d) Reproduced with permission.^{[ 199 ]} Copyright 2019, American Chemical Society. e,f) Raman shift map of the A vibration mode and PL map of a CVD‐grown Mo_{1− x} W _x S₂ alloy domain with graded composition distribution. g) Composition as a function of position along the white arrow marked in (e). h) Schematic illustration of the diffusion‐exchange mechanism and the energies of the reaction steps for the inward diffusion of a Mo atom accompanied by the outward diffusion of a W atom and a S vacancy.^{[ 230 ]} e–h) Reproduced with permission.^{[ 230 ]} Copyright 2018, Nature Publishing Group.