Synthesis of WS_2xSe_2–2x Alloy Nanosheets with Composition-Tunable Electronic Properties

Abstract

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently emerged as a new class of atomically thin semiconductors for diverse electronic, optoelectronic, and valleytronic applications. To explore the full potential of these 2D semiconductors requires a precise control of their band gap and electronic properties, which represents a significant challenge in 2D material systems. Here we demonstrate a systematic control of the electronic properties of 2D-TMDs by creating mixed alloys of the intrinsically p-type WSe2 and intrinsically n-type WS2 with variable alloy compositions. We show that a series of WS2xSe2-2x alloy nanosheets can be synthesized with fully tunable chemical compositions and optical properties. Electrical transport studies using back-gated field effect transistors demonstrate that charge carrier types and threshold voltages of the alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. A highly p-type behavior is observed in selenium-rich alloy, which gradually shifts to lightly p-type, and then switches to lightly n-type characteristics with the increasing sulfur atomic ratio, and eventually evolves into highly n-doped semiconductors in sulfur-rich alloys. The synthesis of WS2xSe2-2x nanosheets with tunable optical and electronic properties represents a critical step toward rational design of 2D electronics with tailored spectral responses and device characteristics.

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.…”

“…The drain–source current is controlled by the gate voltage on the dielectric layer. High carrier mobility, high switching ratio and low subthreshold swing means high performance FET, which depends on the metal contacts,247 channel materials (thickness,248, 249 doping,192, 250, 251, 252, 253, 254 heterostructures200, 208), dielectric materials (back‐gate,86, 255 top‐gate,256 liquid gate257), and so forth. 2D GIVMCs based FETs have demonstrated exciting performance.…”

Interlayer Nanoarchitectonics of Two‐Dimensional Transition‐Metal Dichalcogenides Nanosheets for Energy Storage and Conversion Applications

“…[1][2][3][4][5] Owing to their high anisotropy and unique crystal structures, MX 2 can be utilized in a variety of energy conversion and storage applications, including water splitting cells, rechargeable batteries, supercapacitors, fuel cells, as well as various electronic and optoelectronic devices, etc. [6][7][8][9][10][11] Nanoengineering (morphology, size, number of layers, edges, defects), [12][13][14][15][16][17] phase conversion, [18][19][20][21][22][23] and composition tuning (alloying, doping with foreign transition metal), [24][25][26][27][28][29][30][31] represent the hot research areas in the recent past, aiming at modulation of the material properties and improvement of the device performances. Such impressive progress benefits from the success in synthesizing nanostructured MX 2 with precisely controlled parameters including edge density and crystalline phase.…”

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

“…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]. The resulting alloy nanosheets were monolayers with a well-defined triangular shape, as identified by optical contrast and atomic force microscopy besides Raman spectroscopy [69].…”