졸-겔법으로 성장된 산화아연마그네슘 박막의 전구체의 종류와 농도에 따른 구조적, 광학적 특성 연구

Abstract

ZnO is a typical II-VI group compound semiconductor and oxide semiconductor with a direct and wide band gap (3.37 eV). ZnO has been studied in various fields based on its excellent physical properties. Among them, band gap engineering of ZnO is one of the main research issues in ZnO based material. When the MgO are appropriately replaced by ZnO, it can tailor the band gap to the wider value. Based on this, the alloy of ZnO and MgO can be applied to the active layer of UV-LEDs and high mobility field effect transistors and window layer for solar cell. Furthermore MgZnO can be used in power semiconductor devices. For the formation of MgxZn1-xO films, we explored the sol-gel method that is one of most popular solution based method and easily handle to deposit. The films were grown by spin coating with a ZnO solution and a MgxZn1-xO solution on a Si (100) substrate. In order to study the characteristics of the MgxZn1-xO films, the films prepared by two types of Mg precursor. For the solution synthesis, Zn acetate dihydrate [Zn(CH3COO)2·2H2O] was used as a Zn precursor, and Mg acetate tetrahydrate [Mg(CH3COO)2⋅4H2O] and Mg nitrate hexahydrate [Mg(NO3)2⋅6H2O] each type of Mg precursor was used, respectively. Moreover, the molarity of the Zn precursor to the solvent was varied to be 0.1 M, 0.3 M, and 0.5 M. Also we investigated the effect of the contents of MgxZn1-xO with the inclusion of Mg2+ / Zn2+ proportions up to 0%, 10%, 20%, and 30%. The optical characteristics are measured by a UV-vis spectrophotometer, and the structural characteristics are measured by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Compositional analysis was performed using an energy dispersive X-ray spectrometer (EDS). Both of Mg precursors were successfully used to deposit the MgxZn1-xO thin films and able to control the mole fractions of Mg up to 30%. Also, the increase of mole fraction of Mg in MgxZn1-xO thin films caused a change in the growth mode from (002) textyre growth of ZnO film to random growth of Mg0.3Zn0.7O and the reducing of c-axis length. Futhermore, as the mole fraction of Mg increased, the band gap energy increased. The films using Mg acetate as a Mg precursor kept a grain its size 0f 20 nm regardless of mole fraction of Mg in the films and thickness of films increased linearly with mole fraction of Mg. The films using Mg nitrate as a Mg precursor showed a smallest c-axis length of 5.186 Å and a biggiest band gap energy of 3.63 eV when 30% Mg is contained. The increase in Zn concentration of precursor solution also had an important effect on the properties of ZnMgO films. As the Zn molarity increased, the thickness of films was thicker. The 0.1 M samples showed a smallest in grain size however bandgap energy has the larges one. the film with maximum band gap energy obtained using Mg nitrate at 0.1 M. On the other hand, the films with 0.3 M showed consistent characteristics for Mg content. And the transmittance was most improved up to 15% compared with others. the 0.5 M samples showed poor structural and optical properties due to the high Zn concentration.