Density of States in Amorphous In-Ga-Zn-O Thin-Film Transistor under Negative Bias Illumination Stress

Abstract

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors on glass substrates were fabricated, and the density of state (DOS) in TFTs after a negative bias stress (NBS) and negative bias illumination stress (NBIS) was investigated. For a NBIS of −20 V, the threshold voltage (Vth) shifted toward the negative direction but an increase of shallow states expected as positively ionized oxygen vacancies (Vo+ or Vo++) were not observed in the DOS curves. On the other hand, for NBIS of −30 V, changes in the DOS near the conduction band edge before and after applying a bias stress were observed. This suggests that Vo+ or Vo++ was generated by NBIS but accumulation of holes at the a-IGZO/SiO2 interface mainly caused the Vth shifts.