High Quality Sn-Doped In 2 O 3 Films Grown by Pulsed Laser Deposition for Organic Light-Emitting Diodes
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High Quality Sn-Doped In2O3 Films Grown by Pulsed Laser Deposition for Organic Light-Emitting Diodes Heungsoo Kim,1 James S. Horwitz,1 Woo Hong Kim,2 Zakya H. Kafafi,2 Douglas B. Chrisey1 Code 6372 1 and Code 5615 2 Naval Research Laboratory, 4555 Overlook Avenue, SW, Washington DC, 20375, U.S.A. ABSTRACT High quality Sn-doped In2O3 (ITO) thin films have been grown by pulsed laser deposition (PLD) on glass, flexible polyethylene terephthalate (PET) and single crystal yttria stabilized zirconia (YSZ) substrates for use in organic light emitting diodes (OLEDs). Critical electrode issues for the OLED are related to the optical transparency, electrical resistivity, work function and surface roughness of the ITO film. Our research has focused on improving the properties of the ITO film to increase the efficiency of the OLED. Films were deposited using a KrF excimer laser (248nm, 30 ns FWHM) at fluences of 2 J/cm2 at substrate temperatures ranging from 25°C to 300°C in oxygen pressures ranging from 1 to 100 mTorr. For ITO films (~ 100 nm thick) deposited at the optimized conditions, a resistivity of 4.1 x 10-4 Ω-cm, 2.2 x 10-4 Ω-cm, 1.8 x 10-4 Ω-cm was observed on PET, glass and YSZ, respectively. The average film transmission in the visible range (400 - 700 nm) was about 90 % and the film surface roughness was about 0.5 nm for the film grown on glass. The Hall mobility and carrier density for ITO films (300 nm thickness) were observed to be in the range of 28 - 34 cm2/V-s and 1.0 – 1.2 x 1021 cm-3, respectively. We have used the ITO films, deposited by PLD on glass, plastic and single crystal YSZ substrates, as an anode contact in OLEDs. The OLED device performance based on PLD ITO anodes is compared with that of the device fabricated on the commercial ITO anode.
INTRODUCTION Transparent conducting oxide (TCO) films have been used extensively in the optoelectronic industry because they exhibit high electrical conductivity, high optical transmittance in the visible region and high reflectance in the infrared (IR) region. TCO films have been widely utilized as an essential part of many optoelectronic devices: transparent electrodes in flat panel displays and solar cells; transparent heating elements for automobile and aircraft windows; transparent heat reflecting window material for buildings, lamps, and solar collectors; gas sensors; and antireflection coatings. A large number of TCO materials have been investigated over the years such as In2O3, SnO2, ZnO, CdO as well as their doped oxides [1]. Although most research on TCO materials has been focused on the above oxides, there have been some efforts on making multicomponent oxides to improve the electrical conductivity and optical transparency of the films, such as Ga2O3-In2O3, In2O3-ZnO, In2O3-SnO2, ZnO-SnO2, In2O3-MgIn2O4, MgIn2O4-Zn2In2O5, ZnSnO3ZnIn2O5, and ZnIn2O5-GaInO3 [2]. All of TCO materials mentioned above are n-type semiconductors. However, there have been some efforts on developing new p-type TCO films, such as CuAlO2 and CuGaO2 [3]. Of all the TCO f
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