Gallium Doping Effects for Improving Switching Performance of p-Type Copper(I) Oxide Thin-Film Transistors

Copper(I) oxide (Cu₂O), which is obtained from copper(II) oxide (CuO) through a reduction process, is a p-type oxide material with a band gap of 2.1-2.4 eV. However, the switching performance of typical Cu₂O thin-film transistors (TFTs) is poor because the reduction process increases the concentration of oxygen vacancies (V_O), which interfere with the conduction of hole carriers. Ga with high oxygen affinity was doped in Cu₂O thin films to decrease V_O during the reduction process. As a result, the V_O concentration of 1.56 at % for Ga-doped Cu₂O (Ga:Cu₂O) thin films decreased from 20.2 to 7.5% compared to pristine Cu₂O thin films. Accordingly, the subthreshold swing or S-factor, on/off-current ratio (I_on/off), saturation mobility (μ_sat), and threshold voltage (V_th) of Ga:Cu₂O TFTs were improved compared to pristine Cu₂O TFTs with values of 7.72 from 12.50 V/dec, 1.22 × 10⁴ from 2.74 × 10², 0.74 from 0.46 cm²/Vs, and -4.56 from -8.06 V, respectively. These results indicate that Ga plays an important role in improving the switching performance of p-type Cu₂O TFT.