Growth of Bi2O3 Ultrathin Films by Atomic Layer Deposition

Bismuth trioxide (Bi 2 O 3 ) ultrathin films were successfully synthesized on silicon substrates by means of atomic layer deposition (ALD) using Bi(thd) 3 (thd: 2,2,6,6-tetramethyl-3,5-heptanedionato) and H 2 O as precursors. The optimum ALD window was about 270–300 °C, and an ALD-type growth mechanism via surface saturation reaction was identified; the growth rate was about 0.1 Å/cycle. The X-ray diffraction and high-resolution transmission electron microscopy investigation revealed that Bi 2 O 3 films crystallized into a predominant alpha phase above 250 °C. The resistivity at room temperature was about 1.2 × 10 6 Ω·cm, which is also proof of the α-phase of as-deposited Bi 2 O 3 films. In addition, a new method to obtain γ-Bi 2 O 3 film was discovered. The α-Bi 2 O 3 films (synthesized by ALD) transformed into metastable γ-Bi 2 O 3 with preferred orientation (222) after annealing above 512 °C, and γ-phase could persist at room temperature.