Doping-free bandgap tunability in Fe₂O₃ nanostructured films

A tunable bandgap without doping is highly desirable for applications in optoelectronic devices. Herein, we develop a new method which can tune the bandgap without any doping. In the present research, the bandgap of Fe₂O₃ nanostructured films is simply tuned by changing the synthesis temperature. The Fe₂O₃ nanostructured films are synthesized on ITO/glass substrates at temperatures of 1100, 1150, 1200, and 1250 °C using the hot filament metal oxide vapor deposition (HFMOVD) and thermal oxidation techniques. The Fe₂O₃ nanostructured films contain two mixtures of Fe²⁺ and Fe³⁺ cations and two trigonal (α) and cubic (γ) phases. The increase of the Fe²⁺ cations and cubic (γ) phase with the elevated synthesis temperatures lifted the valence band edge, indicating a reduction in the bandgap. The linear bandgap reduction of 0.55 eV without any doping makes the Fe₂O₃ nanostructured films promising materials for applications in bandgap engineering, optoelectronic devices, and energy storage devices.