Three-Dimensional MoS2 Nanosheet Structures: CVD Synthesis, Characterization, and Electrical Properties

Abstract

The proposed study demonstrates a single-step CVD method for synthesizing three-dimensional vertical MoS2 nanosheets. The postulated synthesizing approach employs a temperature ramp with a continuous N2 gas flow during the deposition process. The distinctive signals of MoS2 were revealed via Raman spectroscopy study, and the substantial frequency difference in the characteristic signals supported the bulk nature of the synthesized material. Additionally, XRD measurements sustained the material’s crystallinity and its 2H-MoS2 nature. The FIB cross-sectional analysis provided information on the origin and evolution of the vertical MoS2 structures and their growth mechanisms. The strain energy produced by the compression between MoS2 islands is assumed to primarily drive the formation of vertical MoS2 nanosheets. In addition, vertical MoS2 structures that emerge from micro fissures (cracks) on individual MoS2 islands were observed and examined. For the evaluation of electrical properties, field-effect transistor structures were fabricated on the synthesized material employing standard semiconductor technology. The lateral back-gated field-effect transistors fabricated on the synthesized material showed an n-type behavior with field-effect mobility of 1.46 cm2 V−1 s−1 and an estimated carrier concentration of 4.5 × 1012 cm−2. Furthermore, the effects of a back-gate voltage bias and channel dimensions on the hysteresis effect of FET devices were investigated and quantified.

Defects Contributing to Hysteresis in Few-Layer and Thin-Film MoS2 Memristive Devices

“…The FETs derived from individual flakes had a channel length (L) = and width (W) = , while those from the thin film had L = and W = , as shown in the SEM images of the Figure 3 a,b inset. For detailed information on the deposition and device processing parameters, please refer to the reported work of Mathew, S. et al [ 14 , 24 ].…”

“…The FETs derived from individual flakes had a channel length (L) = 3.5 µm and width (W) = 15.5 µm, while those from the thin film had L = 13.5 µm and W = 50.4 µm, as shown in the SEM images of the Figure 3a,b inset. For detailed information on the deposition and device processing parameters, please refer to the reported work of Mathew, S. et al [14,24]. The Raman spectra obtained from the channel layer of the experimental back-gate FETs based on a MoS 2 flake and thin film are presented in Figure 3a,b, revealing two pronounced first-order Raman active modes of MoS 2 : E 1 2g and A 1g , corresponding to the in-plane vibration of the Mo-S bond along the base plane of the MoS 2 sheets, and the outof-plane vibration of S along the vertical plane of MoS 2 [4,[25][26][27].…”

Evolution of transition metal dichalcogenide film properties during chemical vapor deposition: from monolayer islands to nanowalls

“…Linear structures that arise upon contact with crystallites growing along the substrate surface serve as centers for the formation of crystallites growing perpendicular to the substrate. The detailed mechanism of vertical structures protruding is still under discussion and requires additional investigations [52]. In general, however, when neighboring islands grow large enough so they come into contact, the atomic planes of these crystallites bend upward and expose their edges to precursorreach gaseous phases.…”

Design and performance analysis of double gate vertically stacked MoS2 nanosheet field effect transistor

“…Chung et al [7], Xiong et al [11], Mathew et al [14], lee et al [15], Chen et al, [16] and Shen et al [17] reported NSFET based on TMD/MoS 2 with good performance metrics such as ON to OFF current ratio greater than 10 8 and high ON currents. However, these metrics are outside the range of predicted metrics as per the IRDS projections.…”