Study of Interface States and Dielectric Permittivity of Two-dimensional Tungsten Diselenide by Impedance Measurements*

The dielectric permittivity of material holds great importance for understanding the intrinsic material properties and meanwhile, it's a critical design parameter for the design of novel device structure. In this article, we studied the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of 2-D semiconducting WSe₂ based metal-insulator-semiconductor-metal capacitors under varying gate voltage (V_G), frequency and temperature. The obtained C-V and G-V results show a strong dependence on applied V_G, frequency (1 kHz to 1 MHz), and temperature (78K to 300K). From frequency-dependent C-V response, we extracted interface state density (D_it) by using the high-low frequency method, where D_it values ranging from 3.8 ×10¹⁰ to 3.6×10¹² cm^-2eV^-1 in the depletion region. Furthermore, we calculated the real (ε′), imaginary (ε'') parts of the dielectric constant and loss tangent (tanδ) using C-V and G-V results. The results show that the values of ε′, ε'' and tanδ decrease with increasing frequency and increase with increasing temperature.