# Optical and Transport Properties of Ni-MoS\({}_{2}\)
## 1 Introduction  
In recent years, transition metal dichalcogenides (TMDCs) have attracted great attention owing to their two-dimensional layer structure which is analogous to graphene [1; 2]. As a member of the TMDC family, molybdenum disulfide (MoS\({}_{2}\)) with a direct bandgap is complementary to the graphene and suggests a great potential for logic devices, integrated circuits, and optoelectronics [3; 4; 5; 6]. Therefore, MoS\({}_{2}\) is rallied up as a finite-energy-bandgap alternative to graphene in advanced electronic and photonic device applications [7; 8; 9; 10; 11]. Several interesting properties of MoS\({}_{2}\) have been also studied in terms of the optical properties and electrical structure. For example, [PERSON] et al. reported there is a transition for MoS\({}_{2}\) from an indirect bandgap in the bulk to a direct gap in the few-layer structures [12], which would be desirable and beneficial for TMDC transistor development. [PERSON] et al. investigated the electronic structure of a single MoS\({}_{2}\) monolayer using first-principles calculations [13], and their results point out that a single MoS\({}_{2}\) monolayer is a direct K to K bandgap semiconductor. [PERSON] et al. studied discontinuous characteristics in energy bands that exist at the interface of monolayer and multilayer thin films [14]. [PERSON] et al. carried out a detailed study to understand the behavior of the electrical performance of monolayer MoS\({}_{2}\) field-effect transistors using the chemical vapor deposition method [15]. Furthermore, [PERSON] et al. demonstrated near-field electrical detection of silver nanowire plasmons with the atomically thin semiconductor molybdenum disulfide [16]. In spite of many relevant MoS\({}_{2}\) characteristics being determined, so far little is known about the properties of the doping categories and their effect on optical and electrical characteristics in terms of whether MoS\({}_{2}\) is a monolayer or bulk. A stable \(p\)-type MoS\({}_{2}\) is important for TMDC device applicationsand has been performed by Nb doping against the native \(n\)-type propensity in unintentionally doped MoS\({}_{2}\)[17]. In that study a stable \(p\)-type conduction with a degenerate hole density of \(\sim\)3 \(\times\) 10\({}^{19}\) cm\({}^{-3}\) in MoS\({}_{2}\) has been demonstrated. Furthermore, [PERSON] et al. pointed out that natural MoS\({}_{2}\) was \(p\)-type in the early period [18]. Nevertheless, most studies revealed that MoS\({}_{2}\) ought to be \(n\)-type [19,20]. Among these studies on dopants, little information has been published concerning the material and physical properties for Ni-MoS\({}_{2}\) thin film. Herein, we have also undertaken a series of experiments to analyze the optical and electrical properties of pure MoS\({}_{2}\) and Ni-MoS\({}_{2}\).  
In this paper, both MoS\({}_{2}\) samples with and without the Ni dopant were prepared by the chemical vapor transport (CVT) method. In terms of optical and electrical properties, reflectance (R), transmittance, photoconductivity (PC), and Hall effect measurements were carried out for both samples. A series of experiments results confirmed the Ni dopant effect on fundamental material properties which could provide guidance for further electronic and optoelectronic devices of MoS\({}_{2}\).