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 In(2)O(3) structure is replaced by substitution with zinc and tin in equal molar proportions: In(2-2x)Zn(x)Sn(x)O(3), where x = 0.3. Films grown at 25 and 100 degrees C exhibit electron diffraction patterns (EDPs) typical of amorphous materials. At a deposition temperature of 200 degrees C, evidence of crystallinity begins to appear in the EDP data and becomes more evident in films deposited at 400 degrees 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 degrees C are dependent on the oxygen partial pressure (P(O(2))) during film growth, transitioning from a high-mobility (36 cm(2)/V x s) conductor (sigma approximately 1700 S/cm) at P(O(2)) = 5 mTorr to a high-mobility semiconductor at P(O(2)) approximately 20 mTorr. Field-effect transistors (FETs) prepared with as-deposited amorphous ZITO channel layers on p(+)-Si/300 nm SiO(2) substrates yield FETs with on/off ratios of 10(6), off currents of 10(-8) A, and field-effect saturation mobilities of 10 cm(2)/V x s.