Electrical, optical, and structural characteristics of ITO thin films by krypton and oxygen dual ion-beam assisted evaporation at room temperature

Abstract

Transparent conducting tin-doped indium oxide (ITO) thin films on polycarbonate and glass substrates were deposited without substrate heating and post-deposition annealing using a dual ion-beam assisted evaporation technique, where the bombardment of the growing film surfaces during electron beam evaporation was done using krypton (varied ion flux, J Kr + , and grid acceleration voltage, V a, of the krypton ion source) and oxygen (fixed ion flux and grid acceleration voltage of the oxygen ion source) ion beams. The electrical, optical, and structural effects of krypton ion-beam bombardment of the growing ITO thin films were investigated using Hall-effect measurements, X-ray photoelectron spectroscopy (XPS), UV-visible spectrometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The total film thickness and the deposition rate were 100 nm and 0.06 nm/s, respectively. All ITO films grown with J Kr + =1.92–3.76×10 14 cm −2 s −1 and V a=100–500 V showed an amorphous structure and no other crystalline phases. As J Kr + increased, the electrical conductivity and the optical transmittance of the grown films were improved compared with those of the ITO films deposited using the oxygen ion-beam only. Also, an increase of the bombardment energy by increasing V a of the krypton ion source caused the deterioration of ITO film properties. The conductivity and the optical transmittance of ITO films deposited on polycarbonate substrates were a little lower than those of films on glass substrates. At room-temperature, using optimal growth conditions, the electrical resistivity was as low as 6.4×10 −4 Ω cm with an electron carrier concentration n e=4.3×10 20 cm −3 and a Hall mobility μ H=26.7 cm 2 V −1 s −1, the visible transmittance (at λ=550 nm) was 90%, and optical direct band gap energy 3.8 eV.