Research On Epsilon-Near-Zero Materials And Structures

Transparent conductive oxide?TCO?thin film materials have near-zero dielectric constant?epsilon-near-zero,ENZ?characteristics,and have been widely concerned by researchers because their dielectric constants can be controlled by electric fields,but it is difficult to be accurately measure the change of near-zero dielectric constant under an electric field control in experiment.The TCO materials involved in this paper include indium tin oxide?ITO?and cadmium oxide?CdO?.Through appling the electric filed for the ITO/SiO2/Si stack and the analysis of the fast spectral ellipsometry,the near-zero dielectric constant of the ITO film is controlled under different oxygen partial pressures.The dynamic change process is studied by Drude model;the change law of the dielectric constant of the CdO thin film of high mobility material is controlled by theoretical calculation.The main work is divided into the following two parts:1.Study on the electrical control of near-zero dielectric constant of ITO film.By changing the process conditions?deposition oxygen partial pressure,deposition temperature and annealing temperature?,the near-zero dielectric constant of the ITO film can be adjusted.We used spectroscopic ellipsometry to characterize the ITO films deposited under different oxygen partial pressures.Based on the Drude model and the Thomas-Fermi Screening model,we used a two-layer model and a gradient-layer model to fit the near-zero dielectric constant of the ITO film at different voltages.Both models show that the optical constants of ITO thin films deposited at 10 Pa have the largest change under electrical field.The specific values are as follows:when the electric field is 2.5MV/cm,the change of refractive index and extinction coefficient of the accumulation layer of the ITO film in the double-layer model at 10 Pa are 0.061 and0.079 at a wavelength of 1550 nm,respectively,and the ENZ wavelength is blue-shifted to 27.9 nm.When the electric field is 2.5 MV/cm,the change of refractive index and extinction coefficient of the accumulation layer of the ITO film in the gradient layer model at 10 Pa are 0.150,0.275 at a wavelength of 1550 nm,respectively,and ENZ wavelength blue shifted to 102.4 nm.2.Research on electrical control of near-zero dielectric constant of CdO thin films.Firstly,according to the Drude model theory,the optical constants change of the accumulation layer of the CdO thin film under different dielectric layers?including SiO2and HfO2?was calculated.The specific rules are as follows:when the electric field is 5MV/cm,the carrier concentrations of accumulation layer corresponding to the dielectric layer SiO₂ and HfO₂ increase by 1.08?10²⁰ cm^-3 and 6.91?10²⁰ cm^-3,respectively.The ENZ wavelengths are blue shifted by 1.11?m,2.32?m,and increased the plasma frequency by 0.54?10¹55 rad/s and 2.23?10¹55 rad/s,respectively.At a wavelength of1550 nm,the refractive index decreased by?35?n?SiO₂?=0.28,?35?n?HfO₂?=2.048,and the extinction coefficient increased by?35???SiO₂?=0.012,?35???HfO₂?=1.642,respectively.It is proved that the use of high mobility ENZ material and high-k oxide thin film can effectively control the dielectric constant of the material by electric field.Secondly,the pulse-laser deposition was used to preliminarily deposit the CdO film in the experiment,which showed that the decrease of the oxygen partial pressure and the increase of the annealing temperature increased the carrier concentrations in the CdO film,thereby reducing its refractive index and increasing its extinction coefficient.