Growth of Bi 2O 3 ultrathin films by atomic layer deposition

Abstract

Bismuth trioxide (Bi 2O 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 2O 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 2O 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 2O 3 films. In addition, a new method to obtain γ-Bi 2O 3 film was discovered. The α-Bi 2O 3 films (synthesized by ALD) transformed into metastable γ-Bi 2O 3 with preferred orientation (222) after annealing above 512 °C, and γ-phase could persist at room temperature. © 2012 American Chemical Society.