CVD synthesis of Mo_(1−x)W_xS₂and MoS_2(1−x)Se_2xalloy monolayers aimed at tuning the bandgap of molybdenum disulfide

Abstract

As a rising star in two-dimensional (2D) layered materials, transition metal dichalcogenides (TMDs) have attracted tremendous attention for their potential applications in nanoelectronics, optoelectronics and photonics. Driven by the high standards of practical devices, alloying theory has been proposed for modulating the electronic structure of TMDs materials as well as their physical and chemical properties. To date, however, very limited alloy materials can be synthesized by chemical vapor deposition (CVD) and a very limited band gap range can be achieved. Herein, for the first time, we report a one-step CVD strategy for the growth of ternary alloy Mo(1-x)WxS2 monolayers (ML) on SiO2/Si substrates with controllable composition. Both Mo(1-x)WxS2 and MoS2(1-x)Se2x alloy materials with high crystallinity were synthesized in this study. Therefore, the bandgap photoluminescence (PL) can be broaden from 1.97 eV (for ML-WS2) to 1.55 eV (for ML-MoSe2). Furthermore, density functional theory calculations were performed to reveal the important role of alloying in tailoring the electronic structure of 2D materials.

Booming Development of Group IV–VI Semiconductors: Fresh Blood of 2D Family

“…Ternary alloys have attracted intensive attention in recent years due to the varied properties through doping the third elements into the pure binary systems, which may provide an important versatility in low‐power consumption electronics and optoelectroncis 189, 190, 191, 192, 193, 194. For example, Pb 1–x Sn x Se is a narrow direct bandgap semiconductor with promising applications in mid‐infrared photodetection (1–3 μm), topological crystalline insulators and high‐speed logic devices due to the doping of Pb 104, 107, 195, 196.…”

Scalable Fabrication of 2D Semiconducting Crystals for Future Electronics

“…Both theoretical calculation and experiments have demonstrated that the band gap of 2D TMDC alloys can be modulated in a wide spectrum range by changing the composition [36]. This is a desired property for many applications in electronic and optoelectronics and has stimulated great efforts in controllable fabrication of various 2D TMDC alloys.…”

“…In particular, the ALD-based super-cycle process is anticipated to apply also to other 2D TMDC alloys than Mo1−xWxS2. Meanwhile, Zhang et al [36] also developed a CVD process to synthesize 2D Mo1−xWxS2 alloys. They used a mixture of WO3 and MoO3 powders as the metal precursor and sulfur powder as the chalcogen precursor.…”

“…The other process [36,39] uses mixed S and Se fine powders as the chalcogen source and MoO3 as the metal source (Figure 14f). By changing the ratio of the S and Se powders in the source, the fraction in the alloy can be well controlled with x ranging from 0-0.75.…”

Band Gap Engineering of Hybrid 2-D Nanomaterials Some Recent Developments

“…Band gap engineered nanosheets were successfully produced using precursors from mechanically exfoliated MoS 2 (1-x) Se 2x bulk alloy showing triangular nanosheets (SEM) with the edge lengths of 30-80 micron. Lateral composition-graded 2D-MoS 2(1-x) Se 2x nano layers were also synthesized employing a simple moving source thermal evaporation method of an improved CVD [55][56][57][58][59][60][61][62][63][64][65][66][67][68]. Subsequently, 2D-WS 2x Se 2(1-x) alloys were prepared from WO 3 (monoclinic crystal) to WS 2 (1-x) Se 2x (hexagonal crystal) through simultaneous sulfurization and selenization, in which, the chemical activity of S made it easy to tune the value of x by varying the weight of sulfur powder [69].…”