Thermal annealing effects on the electrophysical characteristics of sputtered MoS₂ thin films by Hall effect measurements

Abstract

Transition-metal dichalcogenide (MoS 2 ) is gaining increasing attention as a promising highperformance material in practical applications because of its wide-range electrical properties. However, the effect of thermal annealing on the electrophysical characteristics of MoS 2 remains unclear. In this study, the physical and electrophysical properties of MoS 2 thin films were characterized by Hall effect measurements. Large-area and high-quality MoS 2 thin films were obtained by RF sputtering and then subjected to ex situ thermal annealing. As the thermal annealing temperature was increased, the crystallinity of the MoS 2 thin films improved and the corresponding Fermi level shifted toward the valence band. At thermal annealing temperatures above 900 °C, the conductivity type of the MoS 2 thin films changed from the intrinsic n-type to p-type due to the emergence of MoO 3 . In addition, the orientation of the Hall coefficient was indefinite under thermal annealing, implying the electrical transport anisotropy of the MoS 2 thin films, which can be attributed to the spin-orbit coupling of the exposed Mo atoms in the films with sulfur vacancies. Furthermore, the Hall mobility and carrier concentration of the annealed MoS 2 thin films were up to 4.40 cm 2 V −1 s −1 and 12.5×10 16 cm −3 , respectively, at a Hall testing temperature of 305 K and an external magnetic field of 0.5 T.

Effects of Deposition and Annealing Temperature on the Structure and Optical Band Gap of MoS2 Films

“…Figure 4a, each deposition temperature has a sharp peak at 62 • corresponding to MoS 2 (107), and a relatively weak peak corresponds to MoS 2 (100) when the deposition temperature is higher than 50 • at 33.3 • . As shown in Figure 4b, two sharp peaks appear at 69.4 • and 69.6 • corresponding to MoS 2 (202) and Si (100), respectively, the 33.3 • peak corresponds to MoS 2 (100), and the 61.9 • peak corresponds to the MoS 2 (107) plane, it is consistent with the XRD data in the literature [6,31,38]. Combined with the SEM results, the films are granular when the deposition temperature is low, and the growth rate is fast around this time.…”

“…A similar situation is found in the literature. When the deposition temperature is low, a granular surface morphology is easy to deposit, which is consistent with the SEM images observed in the literature [31]. A vertically aligned MoS2 films is easy to form with the increase in temperature [36,37].…”

“…This condition may be because of the difference in the mechanism of sulfur diffusion and the formation of MoS2 before and after annealing, thereby leading to changes in the morphology of the films. At the same time, high-temperature annealing can effectively improve the atomic mobility of the films, thereby allowing the atoms to be located in their energy matching position and improving the stability of the films [31]. Comparing the figures in Figure 2, the deposition temperature of 200 °C is the turning point of the surface structure of the films.…”

“…After annealing, the MoS 2 films have a Hall mobility of 4.40 cm 2 /Vs and a carrier concentration of 12.5 × 1016 cm −3 . After annealing, the hysteresis voltage of the films can be expanded from 8.0 V to 28.4 V [31,32]. Heterostructures, such as Ni-MoS 2 structure, can also be obtained through magnetron sputtering.…”

Effect of Deposition Pressure on the Microstructure and Optical Band Gap of Molybdenum Disulfide Films Prepared by Magnetron Sputtering

“…Advances in technology have increased the demand for various materials, and optoelectronic materials with adjustable band gaps and high stability have become research hotspots [1][2][3]. MoS 2 materials, with alterable band gaps and excellent physicochemical stability, have attracted considerable research interest [4][5][6][7][8][9][10]. MoS 2 is a transition metal disulfide with large global reserves and high stability that has long been used as a solid lubricant in various fields [11][12][13].…”