Boron 이온 주입을 통한 Al 도핑된 ZnO 박막의 일함수 향상

Abstract

ZnO thin films have been extensively studied for their practical uses such as in a flat panel display, solar cell, smart window, and touch screen. In most applications, the ZnO thin films are used as a Transparent Conducting Oxide (TCO). TCOs have to have good transparency of more than 80% and low resistivity of lower than 10-3 Ωcm expecially in the case of their use in the display application. Up to now, indium tin oxide (ITO) has been widely used for the TCO application because of its good conductivity and easy processing. However it has an expensive element of In. ITO is unstable at high temperature and when treated with hydrogen plasma. So many researchers have tried to replace ITO with ZnO. Intrinsic ZnO has a high resistivity of 10-3 Ωcm. Recently through the Al or Ga doping, ZnO has become a potential candidate for application of TCO. A OLED (Orgarnic Light Emitting Diode) is another important field that a ZnO TCO can be applied to. There have been various efforts to increase the work function for higher hole injection efficiency between the anode and hole injection layers. Many researchers have conducted research in areas of developing new materials, introducing self-assembled monolayers, and modifying the TCO surface with oxygen plasma. In spite of various techniques, up to now, we have not obtained the best work function for the TCO. In this study, through B+ ion implantation, the work function and other electrical and optical properties have been controlled. The resistance of the B+ ion implanted aluminum doped zinc oxide (AZO) thin films is decreased as the ion dose and ion energy are increased compared to un-implanted AZO films. The transmittance measurement shows high transmittance of up to 92 % from 200 to 800 nm wavelength range. The work function of AZO is increased by 0.3 eV with 1*1016 /cm2 dose and 5 keV implantation condition. Resistance and transmittance properties of the implanted ZnO degrade slightly compared to un-implanted ZnO films. The Above results could be explained through the doping profile and consideration of the resultant band diagram. The coupling between B+ ion and oxygen vacancy is suggested to be the main reason for the work function increase and other properties changes. Our study implied that if we can control the defect density of the TCO top layer, we can control the work function effectively. In detail, our study suggests that a very thin functionally gradient materials on the general structure TCO be the best structure for TCO thin film.