Synthesis of Inorganic Semiconductor Films with Narrow Bandgap Responsive to Visible LEDs and their Photo-Response

Anatase-type TiO 2 films synthesised on quartz glass demonstrated cell adhesion control when illuminated from the backside with a 150 W Xe lamp emitting white light. The UV component was fully absorbed by the TiO 2 film, preventing cell exposure to it. By selectively applying localised light, non-contact control of cell adhesion areas was achieved. If non-toxic films responsive to conventional LED panels could be used, this would enable precise and easy control of cell adhesion areas. The purpose of this study was to synthesise inorganic semiconductor films with a narrower bandgap than TiO 2 , responding to visible light from LED, and to investigate their photo-responsive properties. α-Fe 2 O 3 films were deposited on borosilicate glass or ITO-coated quartz glass using RF sputtering with the corresponding metallic targets under an Ar or Ar/O 2 mixed atmosphere. XRD analysis showed sharp diffraction peaks, confirming the successful synthesis of the films. The absorption edges of the oxides shifted to longer wavelengths compared to that of TiO 2 , corresponding to their bandgap differences. When a tablet device (HUAWEI MediaPad M3 Lite 10wp) displaying a white image was used as a light source, the oxide films showed a noticeable photocurrent. In the photocurrent profile during the on/off cycle of the light, a phenomenon of current flowing in the reverse direction when the light was turned off was observed. Moreover, this current reversal was more pronounced when the grains were fine. This suggests that the grain boundaries acted like a capacitor and induced polarisation behaviour.