Reduction of surface plasma loss of indium tin oxide thin films by regulating substrate temperature

Abstract

Indium tin oxide (ITO) thin films,as a heavy doping n-type semiconductor material with a high carrier concentration,can realize the surface plasma effect and regulation of surface plasmon resonance wavelength in the near infrared region:the surface plasma has broad application prospect in surface plasmon devices.The ITO thin films are deposited on float glass substrates (20 mm20 mm) via the direct current (DC) magnetron sputtering by regulating substrate temperature from 100 ℃ to 500 ℃.The deposited ITO thin films present a cubic polycrystalline iron manganese structure,in which the ITO film shows the strong crystallinity at 400 ℃,so that it is conducive to reducing the defects of bound electrons and the damping force of thin film.The surface roughness of ITO thin film first decreases and then increases with the temperature increasing,correspondingly the root-mean-square roughness (Rq) of these films decreases from 4.11~nm to 2.19 nm,then increases to 2.56 nm.The Rqvalue of 2.19 nm corresponds to a preferable surface smoothness of ITO thin film,indicating that it can effectively increase carrier concentration of ITO thin film at 400 ℃.The effects of the different substrate temperature on the photoelectric and surface plasma properties of ITO thin films are analyzed by UV-Vis absorption spectra,Hall measurement,refractive index and dielectric constant.As the temperature increases from 100 ℃ to 500 ℃,the carrier concentration of ITO thin film is enhanced from 4.11020 cm-3 to 2.481021 cm-3,and thus increasing the probability of the Fermi level to the conduction band of ITO thin film.And the enhancement of carrier concentration induces the Moss-Burstein effect,which makes the edges of absorption spectrum of the ITO thin film gradually blue-shift from 340 nm to 312 nm,correspondingly broadening the optical band gap from 3.64 eV to 3.97 eV.These results cause the difficulties of electrons interband transition to be enhanced,and thus suppressing the phenomenon of absorbing photons for the electron transition from low level to high level,which ultimately reduces the optical loss of ITO thin film.In addition,the surface plasma effect is realized in a range from 1100 nm to 1700 nm for ITO thin film by regulating the substrate temperature.Meanwhile,the electronic mobility in the ITO thin film is also improved from 24.6 cm2V-1s-1 to 32.2 cm2V-1s-1,which reduces the electronic scattering,and is beneficial to the increase of propagation length of surface plasma waves.The above results imply that we have attained the goal of the reducing the electrical loss of ITO thin film.