Metal-organic chemical vapor deposition of indium oxide based transparent conducting oxide thin films: Precursor synthesis, film growth and characterization, and their application in polymer light-emitting diode devices.

摘要

Four novel diamine adducts of bis(hexafluoroacetylacetonato)zinc [Zn(hfa)2·(diamine)] can be synthesized in a single step reaction. Single crystal x-ray diffraction studies reveal monomeric, six-coordinate structures. The thermal stabilities and vapor phase transport properties of these complexes are considerably greater than those of conventional solid/liquid zinc metal-organic chemical vapor deposition (MOCVD) precursors. Of the four complexes, bis(1,1,1,5,5,5-hexafluoro-2,4-pentadionato)(N,N '-diethylethylenediamine)zinc [Zn(hfa)2 ( N,N'-DEA)], is particularly effective in the growth of thin films of the transparent conducting oxide Zn- and Sn-doped In2O3 (ZITO) due to its superior volatility and low melting point of 64°C.; ZITO (ZnInxSnyOz, 1.5 x 4.0, 0.5 y 2.5) thin films with In contents ranging from 40--70 cation % (a metastable phase) were grown by low pressure MOCVD using volatile precursors tris(2,2,6,6-tetramethyl-3,5-heptanedionato)indium [In(dpm) 3], bis(2,4-pentanedionato)tin [Sn(acac)2], and Zn(hfa) 2(N,N'-DEA). These films exhibit conductivity as high as 2900 S/cm and optical transparency comparable to or greater than that of commercial ITO (Sn-doped indium oxide) films. They are more stable under acidic conditions than commercial ITO films as evidenced by XPS studies. Polymer light emitting diode (PLED) devices based on ZnIn 2.00Sn1.50Oz anode exhibit maximum light output of 4500 cd/m2 and current efficiency of 0.85 cd/A, which are 70% and 80% higher than those of PLED devices based on commercial ITO anode, respectively. The increased performance of ZITO based devices is attributed to the decreased reactivity of ZITO anode towards the acidic PEDOT-PSS hole injection layer compared to ITO anode.; MITO (MgInxSnyOz, 6.0 x 16.0; 3.0 y 8.0, a metastable phase) thin films were grown by low-pressure MOCVD using volatile precursors In(dpm)3, Sn(acac)2, and bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(tetramethylmethylenediamine)magnesium [Mg(dpm)2(TMEDA)]. Films in this compositional range retain the cubic In2O3 bixbyite crystal structure. The highest conductivity is found to be ∼1000 S/cm (n-type, carrier concentration = 1.72 x 1020 cm-3, mobility = 35.7 cm2/Vs) for films with nominal composition MgIn14.3Sn 6.93Oz. The optical transmission window of the present films is much wider than that of typical ITO films from 300 nm to 3300 nm, and the transmittance is greater than or comparable to that of commercial ITO films.