A homojunction-structured oxide phototransistor based on a mechano-chemically treated indium–gallium–zinc oxide (IGZO) absorption layer is reported. Through this novel and facile mechano-chemical treatment, mechanical removal of the cellophane adhesive tape induces reactive radicals and organic compounds on the sputtered IGZO film surface. Surface modification, following the mechano-chemical treatment, caused porous sites in the solution-processed IGZO film, which can give rise to a homojunction-porous IGZO (HPI) layer and generate sub-gap states from oxygen-related defects. These intentionally generated sub-gap states played a key role in photoelectron generation under illumination with relatively long-wavelength visible light despite the wide band gap of IGZO (>3.0 eV). Compared with conventional IGZO phototransistors, our HPI phototransistor displayed outstanding optoelectronic characteristics and sensitivity; we measured a threshold voltage (V th) shift from 3.64 to −6.27 V and an on/off current ratio shift from 4.21 × 1010 to 4.92 × 102 under illumination with a 532 nm green light of 10 mW/mm2 intensity and calculated a photosensitivity of 1.16 × 108. The remarkable optoelectronic characteristics and high optical transparency suggest optical sensor applications.

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The electrical properties and device stability of a self-aligned (SA) coplanar amorphous indium−gallium−zinc oxide (a-IGZO) thin-film transistor (TFT) were investigated by implanting boron (B) into the source/drain (SD) n + region. To evaluate the effect according to the depth profile of B in the a-IGZO film, various implantation energies were applied. The electrical properties were optimized when the projection range of B was in the central vertical region of the a-IGZO film. B implantation decreased the resistivity of the a-IGZO film from 3.1 × 10 2 to 2.1 × 10 −3 Ω•cm compared to an untreated a-IGZO film, while the field-effect mobility (μ fe ) improved from 2.96 to 17.22 cm 2 /(V•s). Moreover, the fabricated SA coplanar a-IGZO TFTs with a B-doped n + region exhibited excellent stability, with a threshold voltage shift (ΔV th ) of <0.2 V during a 3000 s thermal stability test performed at 200 °C and a bias stress test under a gate voltage of ±20 V. During the implantation process, B ions with high kinetic energy collide with IGZO atoms, resulting in the formation of an oxygen vacancy (V O ) and an oxygen interstitial (O i ) simultaneously. The implanted B ions and O i are bonded such that the V O sites are maintained by the B−O reaction and can contribute to an increase in the carrier concentration in a-IGZO films, thereby increasing the conductivity of the n + region.

In this paper, a transparent phototransistor with improved visible light detection by applying sub gap states engineering and a porous polytetrafluoroethylene (PTFE) layer on the indium–gallium–zinc oxide (IGZO) thin film is introduced. The porous PTFE film was sputtered with the selective etching process through an oxygen plasma process after removing nickel nanoparticles dispersed by a magnetic field with a liftoff process. The photoresponse characteristics of porous PTFE/IGZO (PPI) phototransistors were tested with various thicknesses of PTFE (15–75; 15 nm steps). The PPI phototransistor with the PTFE thickness of 30 nm showed the highest photoresponse properties. Although the measured optical bandgap energy of the IGZO film was 3.87 eV, the PPI phototransistors could detect visible light due to the trap-assisted electron/hole pair generation by the sub gap states of the IGZO film induced by plasma damage during PTFE deposition. In addition, it was possible to maximize the efficiency of detecting visible light by capturing and scattering light with the porous structure of PTFE. The PPI phototransistors had a photoresponsivity of 73.45 ± 16.14 A/W, photosensitivity of (1.60 ± 0.57) × 106, and detectivity of (2.62 ± 2.37) × 1010 Jones under illumination by red light with a wavelength of 635 nm and an intensity of 10 mW/mm2.

We propose indium gallium zinc oxide (IGZO) phototransistors with an extended wavelength detection range by a capping layer composed of hafnium oxide (HfO2). A HfO2 capping layer enables the generation of oxygen vacancies by strongly attracting oxygen ions in the back channel of IGZO. IGZO phototransistors with the capping layer exhibit improved optoelectronic characteristics, such as photoresponsivity of 149.48 A/W, photosensitivity of 1.17 × 106, detectivity of 3.64 × 1010 Jones under the green light (532 nm) illumination of 10 mW/mm2.