Journal of Information Display

  • 제9권4호
  • /
  • Pages.21-29
  • /
  • 2008
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  • 1598-0316(pISSN)
  • /
  • 2158-1606(eISSN)
한국정보디스플레이학회 (The Korean Infomation Display Society)
권호 표지

Photofield-Effect in Amorphous In-Ga-Zn-O (a-IGZO) Thin-Film Transistors

  • Fung, Tze-Ching (Department of Electrical Engineering and Computer Science, University of Michigan) ;
  • Chuang, Chiao-Shun (Department of Photonics & Display Institute, National Chiao Tung University) ;
  • Nomura, Kenji (ERATO-SORST, JST, in Frontier Collaborative Research Center / Material and Structure Lab., Tokyo Institute of Technology) ;
  • Shieh, Han-Ping David (Department of Photonics & Display Institute, National Chiao Tung University) ;
  • Hosono, Hideo (ERATO-SORST, JST, in Frontier Collaborative Research Center / Material and Structure Lab., Tokyo Institute of Technology) ;
  • Kanicki, Jerzy (Department of Electrical Engineering and Computer Science, University of Michigan)
  • 발행 : 2008.12.30
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초록

We studied both the wavelength and intensity dependent photo-responses (photofield-effect) in amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs). During the a-IGZO TFT illumination with the wavelength range from $460\sim660$ nm (visible range), the off-state drain current $(I_{DS_off})$ only slightly increased while a large increase was observed for the wavelength below 400 nm. The observed results are consistent with the optical gap of $\sim$3.05eV extracted from the absorption measurement. The a-IGZO TFT properties under monochromatic illumination ($\lambda$=420nm) with different intensity was also investigated and $I_{DS_off}$ was found to increase with the light intensity. Throughout the study, the field-effect mobility $(\mu_{eff})$ is almost unchanged. But due to photo-generated charge trapping, a negative threshold voltage $(V_{th})$ shift is observed. The mathematical analysis of the photofield-effect suggests that a highly efficient UV photocurrent conversion process in TFT off-region takes place. Finally, a-IGZO mid-gap density-of-states (DOS) was extracted and is more than an order of magnitude lower than reported value for hydrogenated amorphous silicon (a-Si:H), which can explain a good switching properties observed for a-IGZO TFTs.

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