Study of electrical contact properties of 2D metal-semiconductor heterojunctions composed of different phases of NbS<sub>2</sub> and GeS<sub>2</sub>

Abstract

Metal-semiconductor heterojunction (MSJ) is the basis for the development of novel devices. Here, we consider different-phase metals H- and T-NbS<sub>2</sub> and semiconductor GeS<sub>2</sub> to form different two-dimensional van der Waals MSJs, and conduct an in-depth study of their structural stability, electronic and electrical contact properties, with an emphasis on exploring the dependence of the electrical contact properties of the MSJs on the different phases of metals. Calculating binding energies, phonon spectra, AIMD simulations, and mechanical properties show that both heterojunctions are highly stable, meaning that it is possible for experimental preparation and feasible to be used for designing electronic devices. The intrinsic H-NbS<sub>2</sub>/GeS<sub>2</sub> and T-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunctions form p-type Schottky contacts and quasi-n-type Ohmic contacts, respectively. It is also found that their Schottky barrier heights (SBH) and electrical contact types can be effectively modulated by an applied electric field and biaxial strain. For example, for the H-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, Ohmic contacts can be achieved regardless of the application of positive/negative electric field or planar biaxial compression, whereas for the T-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, Ohmic contacts can be achieved only at a very low negative electric field. The planar biaxial stretching can lead to the achievement of quasi-Ohmic contacts. In other words, when the semiconductor GeS<sub>2</sub> monolayer is used as the channel material of the field effect transistors and contacted with different phases of metallic NbS<sub>2</sub> monolayer to form the MSJ, the interfacial Schottky barriers are distinctly different, and each of them has its own advantages in different situations (intrinsic or physically regulated). Therefore, this study is of significant for understanding the physical mechanism of the electrical contact behaviors for H(T)-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, especially for providing the theoretical reference to select the appropriate metal electrodes for the development of highperformance electronic devices.