Narrowing the band gap and suppressing electron-hole recombination in β-Fe2O3 by chlorine doping

The effects of halogen (F, Cl, Br, I, and At) doping in the direct-band-gap beta-Fe2O3 semiconductor on its band structures and electron-hole recombination have been investigated by density functional theory. Doping Br, I, and At in beta-Fe2O3 leads to transformation from a direct-band-gap semiconductor to an indirect-band-gap semiconductor because their atomic radii are too large; however, F- and Cl-doped beta-Fe2O3 remain as direct-band-gap semiconductors. Due to the deep impurity states of the F dopant, this study focuses on the effects of the Cl dopant on the band structures of beta-Fe2O3. Two impurity levels are introduced when Cl is doped into beta-Fe2O3, which narrows the band gap by approximately 0.3 eV. After doping Cl, the light-absorption edge of beta-Fe2O3 redshifts from 650 to 776 nm, indicating that its theoretical solar to hydrogen efficiency for solar water splitting increases from 20.6% to 31.4%. In addition, the effective mass of the holes in halogen-doped beta-Fe2O3 becomes significantly larger than that in undoped beta-Fe2O3, which may suppress electron-hole recombination.

Automated summary

The effects of halogen doping in beta-Fe2O3 semiconductor on its band structures and electron-hole recombination were investigated. Doping Br, I, and At leads to transformation from direct-band-gap semiconductor to indirect-band-gap semiconductor due to large atomic radii. F- and Cl-doped beta-Fe2O3 remain as direct-band-gap semiconductors. Cl dopant narrows the band gap by approximately 0.3 eV and increases the solar to hydrogen efficiency for solar water splitting.