Control and Characterization of the Structural, Electrical, and Optical Properties of Amorphous Zinc−Indium−Tin Oxide Thin Films

Zinc−indium−tin oxide (ZITO) films are grown by pulsed-laser deposition in which 30% of the indium in the In2O3 structure is replaced by substitution with zinc and tin in equal molar proportions: In2−2x Zn x Sn x O3, where x = 0.3. Films grown at 25 and 100 °C exhibit electron diffraction patterns (EDPs) typical of amorphous materials. At a deposition temperature of 200 °C, evidence of crystallinity begins to appear in the EDP data and becomes more evident in films deposited at 400 °C. The advent of crystallinity affects the electrical properties of the ZITO film, and the effect is ascribed to the boundaries between phases in the films. The electrical and optical properties of the amorphous ZITO films grown at 25 °C are dependent on the oxygen partial pressure (P O2 ) during film growth, transitioning from a high-mobility (36 cm2/V·s) conductor (σ ∼1700 S/cm) at P O2 = 5 mTorr to a high-mobility semiconductor at P O2 ≈ 20 mTorr. Field-effect transistors (FETs) prepared with as-deposited amorphous ZITO channel layers on p+-Si/300 nm SiO2 substrates yield FETs with on/off ratios of 106, off currents of 10−8 A, and field-effect saturation mobilities of 10 cm2/V·s.