Growth temperature-dependent phase evolution and photoactivities of sputtering-deposited crystalline Bi2O3 thin films

Abstract

Crystalline Bi(2)O(3)thin films were grown through radio-frequency magnetron sputtering deposition using a bismuth metal target in an Ar/O(2)mixed atmosphere and in an Ar atmosphere with further post-annealing procedures in ambient air. The crystal structures, surface morphologies, and photoactive performance of various as-synthesized Bi(2)O(3)thin films were manipulated by controlling thein situsputtering growth temperature and post-annealing temperature. Structural analysis revealed that thein situsputtering-grown Bi(2)O(3)thin films had dual monoclinic alpha-/tetragonal beta-phase structures below the growth temperature of 425 degrees C with an unexceptional impurity phase of Bi(4)O(7)in the film; the Bi(2)O(3)thin film consisted of a pure single beta phase when the growth temperature was increased above 425 degrees C. In contrast, the sputtering deposited metallic bismuth thin films transformed into pure alpha/beta phase-structured Bi(2)O(3)thin films without any impurity phase when the annealing temperature was below 425 degrees C; however, Bi(4)O(7)was formed in the alpha/beta Bi(2)O(3)film with annealing temperatures above 425 degrees C in this study. For the Bi(2)O(3)thin-film crystal grownvia in situsputtering or annealing, the growth temperature effects on impurity phase generation showed the opposite trend. Furthermore, the formation of the impurity Bi(4)O(7)phase in the Bi(2)O(3)films may deteriorate the photoactive performance of the Bi(2)O(3)thin film. The efficient photoexcited charge separation and transfer across the alpha-beta phase heterojunctions in the polymorph alpha/beta Bi(2)O(3)films accounted for their higher photoactivity among the various Bi(2)O(3)thin films in this study. The results reported herein show that the alpha/beta dual phase Bi(2)O(3)film without any impurity phase formedviaprecise process control is promising for applications in photoactive devices or as a coupling oxide layer in heterogeneous devices.