Artificially Fabricated Subgap States for Visible-Light Absorption in Indium–Gallium–Zinc Oxide Phototransistor with Solution-Processed Oxide Absorption Layer

Abstract

We present a solution-processed oxide absorption layer (SAL) for detecting visible light of long wavelengths (635 and 532 nm) for indium–gallium–zinc oxide (IGZO) phototransistors. The SALs were deposited onto sputtered IGZO using precursor solutions composed of IGZO, which have the same atomic configuration as that of the channel layer, resulting in superior interface characteristics. We artificially generated subgap states in the SAL using a low annealing temperature (200 °C), minimizing the degradation of the electrical characteristics of thin-film transistor. These subgap states improved the photoelectron generation in SALs under visible light of long wavelength despite the wide band gap of IGZO (∼3.7 eV). As a result, IGZO phototransistors with SALs have both high optical transparency and superior optoelectronic characteristics such as a high photoresponsivity of 206 A/W and photosensitivity of ∼106 under the influence of a green (532 nm) laser. Furthermore, endurance tests proved that the IGZO phototransistor with SALs can operate stably under red laser illumination switched on and off at 0.05 Hz for 7200 s.

A visible-light phototransistor based on the heterostructure of ZnO and TiO2 with trap-assisted photocurrent generation

“…23 These organic materials cause a current path with an increase in the off current at a negative voltage range and $10 3 on/off ratio. 21,24,25 In addition, to determine the origin of the unstable transfer curve characteristics of TiO 2 /ZnO TFTs, the chemical states of TiO 2 lms were analyzed with various purge time periods of ALD-TiO 2 (0.5, 10, and 20 s). Fourier transform infrared (FT-IR) spectroscopy was performed to investigate the chemical states related to the organic residues of TiO 2 on ZnO lms.…”

“…20 To resolve these problems, heterostructures based on oxide semiconductors have been suggested instead of organic and other nanomaterials on the wide bandgap oxide semiconductor. 21,22 In this study, we introduced a heterojunction structure based on the oxide semiconductors of titanium oxide (TiO 2 ) and zinc oxide (ZnO) to fabricate a visible-light phototransistor. A TiO 2 layer was deposited onto a spin-coated ZnO via atomic layer deposition (ALD) under various purge time periods of titanium isopropoxide (TTIP) to nd an optimal absorbing TiO 2 layer.…”

A Review of Phototransistors Using Metal Oxide Semiconductors: Research Progress and Future Directions

“…g–i) Reproduced with permission. [ 92 ] Copyright 2019, American Chemical Society. j) Schematic image of IGZO phototransistor with HAL.…”

“…demonstrated a phototransistor with a double‐layered channel structure in which an oxide semiconductor of the same composition was synthesized through different deposition methods. [ 92 ] As shown in Figure 8g, a solution‐processed IGZO absorption layer (SAL) was deposited on the sputter‐processed IGZO phototransistor. The solution process was conducted by spin coating or electrohydrodynamic (EHD) jet printing.…”

Improving the performances of oxide phototransistors using a mechanochemically treated porous visible-light absorption layer

“…The following is the mechanism of the improved detection ability in the IGZO TFTs with a POL. At first, the POL can generate an electron-hole pair under visible light through the physical defects and oxygen due to the generation of subgap states within the bandgap, which is between the valence and conduction bands [16]. Then the generated electrons are transferred to the IGZO channel layer, resulting in increased off current and a negative V th shift.…”