Highly Conductive and Transparent AZO Films Fabricated by PLD as Source/Drain Electrodes for TFTs

Aluminum-doped ZnO (AZO) has huge prospects in the field of conductive electrodes, due to its low price, high transparency, and pro-environment. However, enhancing the conductivity of AZO and realizing ohmic contact between the semiconductor and AZO source/drain (S/D) electrodes without thermal annealing remains a challenge. Here, an approach called pulsed laser deposition (PLD) is reported to improve the comprehensive quality of AZO films due to the high energy of the laser and non-existence of the ion damage. The 80-nm-thick AZO S/D electrodes show remarkable optical properties (transparency: 90.43%, optical band gap: 3.42 eV), good electrical properties (resistivity: 16 × 10^-4 Ω·cm, hall mobility: 3.47 cm²/V·s, carrier concentration: 9.77 × 10²⁰ cm^-3), and superior surface roughness (R_q = 1.15 nm with scanning area of 5 × 5 μm²). More significantly, their corresponding thin film transistor (TFT) with low contact resistance (R_SD = 0.3 MΩ) exhibits excellent performance with a saturation mobility (µ_sat) of 8.59 cm²/V·s, an I_on/I_off ratio of 4.13 × 10⁶, a subthreshold swing (SS) of 0.435 V/decade, as well as good stability under PBS/NBS. Furthermore, the average transparency of the unpatterned multi-films composing this transparent TFT can reach 78.5%. The fabrication of this TFT can be suitably transferred to transparent arrays or flexible substrates, which is in line with the trend of display development.