Thin-film-based multifunctional devices:
For example, to be a high optical sensitivity, a heterojunction oxide channel can be incorporated into thin-film transistor (TFT) structure. One of these layers should be thin and oxygen deficient, like ZnO and InZnO with a high density of oxygen defects (DO), e.g. oxygen vacancies and interstitials, for high optical absorption due to optical ionisation of the oxygen defects, called persistent photoconductivity (PPC). Here, we can think of a bilayer structure where visible light absorption and charge separation are happening, for example, in In-Ga-Zn-O/In-Zn-O (i.e. IGZO/IZO) bi-layer channel TFTs. The other layer is relatively thick and compensated with, e.g. Ga or Hf, thus containing less amount of oxygen defects, hence making them less conductive. The layers in the heterostructure provide a valence band offset, giving rise to effective charge separation for high quantum efficiency. However, as an optimisation issue, the thickness of the light absorption layer should be optimised to get a positive threshold voltage for enhancement mode operation. Although there is visible light absorption, transparency is maintained at higher wavelengths, thus suited for transparent image capture. This kind of research can also lead to a transparent optical memory besides photo-sensors, thus multifunctionality.
Related key publications:
- Sungsik Lee, Sanghun Jeon, Reza Chaji, and Arokia Nathan, “Transparent Semiconducting Oxide Technology for Touch Free Interactive Flexible Displays,” Proceedings of the IEEE 103, 664 (2015).
- Sanghun Jeon, Seung-eon Ahn, Ihun Song, Chang Jung Kim, U-In Chung, Eunha Lee, Inkyung Yoo, Arokia Nathan, Sungsik Lee, John Robertson, and Kinam Kim, “Gated Three-Terminal Device Architecture to Eliminate Persistent Photoconductivity in Oxide Semiconductor Photosensor Arrays,” Nature Materials, vol.11, pp. 301-305, Apr 2012.