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Self-aligned coplanar top gate indium–gallium–zinc-oxide thin-film transistors (TFTs), with source/drain (S/D) regions that were heavily doped by various deep-ultraviolet (DUV) irradiation energies at dual wavelengths of 185 and 254 nm, were investigated. The electrical performances of TFTs improved as the DUV irradiation energy increased. The proposed TFTs, with DUV irradiation of 20 J/cm2, have a field-effect mobility of 22.0 cm2/ \text V\cdot \text s , a threshold voltage of 2.2 V, a subthreshold swing value of 0.24 V/decade, and an on/off current ratio of 1.34 \times 10^6 . In addition, the channel length modulation ( \Delta L ) and the width-normalized contact resistance ( R_{\mathrm {SD}}W ) were 1.04 \mu \text{m} and 60.5 \Omega \cdot \text cm , respectively. Such short \Delta L and low R\mathrm {\mathbf {SD}}W values indicate that the S/D regions were properly formed by the DUV irradiation. This simple and cost-effective doping technique can be useful for the fabrication of self-aligned TFTs. [ABSTRACT FROM PUBLISHER]