Effects of post-deposition vacuum annealing on film characteristics of p-type Cu_2O and its impact on thin film transistor characteristics

摘要

Annealing of cuprous oxide (Cu_2O) thin films in vacuum without phase conversion for subsequent inclusion as the channel layer in p-type thin film transistors (TFTs) has been demonstrated. This is based on a systematic study of vacuum annealing effects on the sputtered p-type Cu_2O as well as the performance of TFTs on the basis of the crystallographic, optical, and electrical characteristics. It was previously believed that high-temperature annealing of Cu_2O thin films would lead to phase conversion. In this work, it was observed that an increase in vacuum annealing temperature leads to an improvement in film crystallinity and a reduction in band tail states based on the X-ray diffraction patterns and a reduction in the Urbach tail, respectively. This gave rise to a considerable increase in the Hall mobility from 0.14 cm~2/V•s of an as-deposited film to 28 cm~2/V•s. It was also observed that intrinsic carrier density reduces significantly from 1.8 × 10~(16) to 1.7 × 10~(13)cm~(-3) as annealing temperature increases. It was found that the TFT performance enhanced significantly, resulting from the improvement in the film quality of the Cu_2O active layer: enhancement in the field-effect mobility and the on/off current ratio, and a reduction in the off-state current. Finally, the bottom-gate staggered p-type TFTs using Cu_2O annealed at 700 ℃ showed a field-effect mobility of ～0.9 cm~2/V•s and an on/off current ratio of ～3.4 × 10~2.