Properties of Bi and BiSb Nano-Dimensional Layers in Thz Frequency Range

Abstract

In the present paper we demonstrate and compare different properties of Bi and Bi1-xSbx thin films placed on polyimide (PI) substrate in frequency range from 0.2 to 1.0 THz. Bi films with a thickness of 40, 105 and 150 nm have been studied as well as 150 nm Bi1-xSbx solid solutions with Sb concentration of 5, 8, 12 and 15 %. An effective refractive index and permittivity of whole substrate/film structures have been derived by using terahertz time-domain spectroscopy (THz-TDS) method. These measurements have shown the positive phase shift in PI substrate with a thickness of 42 μm and revealed that it is barely transparent in studied frequency range, but the whole substrate/film structure provides the negative phase shift of terahertz wave. It was shown that the permittivity depends on mobility of charge carriers which is driven by film thickness and antimony content.