Protein Biophotosensitizer-Based IGZO Photo-thin Film Transistors for Monitoring Harmful Ultraviolet Light

Abstract

The development of health monitoring devices to prevent skin cancers or various diseases arising from exposure to harmful light has attracted increasing scientific interest and has led to the exploration of hybrid inorganicbiological systems through the incorporation of biomolecules. Here, ultraviolet (UV) photodetectors based on transistors incorporating green fluorescent protein (GFP) molecules on multilayer-stacked indium−gallium−zinc-oxide (IGZO) thin films are studied, where the top layer of the IGZO films has different surface properties. Light-sensitive GFP can play a role as a biophotosensitizer due to light-induced electron transfer during photoexcitation. Intriguingly, the IGZO photo-thin film transistors (TFTs) with GFP molecules on a relatively more hydrophilic surface (less defective surface) have better device performance and exhibit a dramatic decrease in the photocurrent after turning the UV light off compared to the cases without GFP molecules on the more hydrophilic surface and on the less hydrophilic surface (more defective surface). A physical mechanism based on energy band diagrams is proposed, and the light-induced threshold voltage shift in the IGZO photo-TFTs is estimated and explained in terms of oxygen-related vacancy sites and trap/interface conditions in the IGZO film and lightinduced electron transfer from the GFP molecules.

Enhanced Ultraviolet Photoresponse Characteristics of Indium Gallium Zinc Oxide Photo-Thin-Film Transistors Enabled by Surface Functionalization of Biomaterials for Real-Time Ultraviolet Monitoring

“…At V GS – V th < 0 V in the dark condition (Figure a,e), we observed the increased surface potential of the BFP/IGZO film from the KPFM results, indicating the surface band bending at the IGZO/BFP interface with an increase in the electron concentration, and this could be the main reason for the significant V th shift in the BFP/IGZO photo-TFTs. When UV light was turned on (Figure b,f), the desorption of oxygen molecules at the IGZO surface and the ionization of oxygen vacancies induced excessive electrons in the conduction band, resulting in the I ph of the IGZO photo-TFTs. , For the BFP/IGZO thin film, the light-induced charge transfer from BFP molecules to the IGZO channel contributed to the increase in I ph in addition to the ionization of oxygen vacancies, resulting in the enhanced UV photoresponse characteristics such as high photoresponsivity and a fast increase in I ph . After UV light was turned off (Figure c,g), the surface potential of the BFP/IGZO thin film considerably decreased, as shown in the KPFM results (Figure c).…”

“…Among them, indium gallium zinc oxide (IGZO) is one of the most promising oxide semiconductor materials for thin-film transistors (TFTs) because of its high field-effect mobility, good film uniformity, and large-area fabrication. , In addition, the UV light absorption characteristics of IGZO due to its wide optical band gap ( E g ) of ∼3.3–3.5 eV , have allowed for various optoelectronic applications based on the TFTs such as transparent electronics, neuromorphic vision sensors, and UV PDs. − In spite of these advantages, however, the relatively weak optical absorption in the UV-A range and the persistent photoconductivity (PPC) hamper the feasibility of IGZO photo-TFTs for high-performance real-time UV monitoring, causing slow photoresponse and low photoresponsivity at low optical power density. It is well known that PPC of amorphous oxide semiconductors results from the oxygen vacancy-related states within the E g of IGZO thin films and lasts for hours/days even in the absence of light .…”

“…It is well known that PPC of amorphous oxide semiconductors results from the oxygen vacancy-related states within the E g of IGZO thin films and lasts for hours/days even in the absence of light . Accordingly, substantial efforts have been devoted to enhance the photoresponse characteristics of IGZO photo-TFTs such as the application of a positive-gate bias pulse, ,, optimization of the metallic component of a thin film, and formation of heterostructures with other materials including perovskites, , polymers, , 2D TMDCs, and biomaterials …”

“…Recently, biomaterial-based electronic devices have been developed due to potential applications including light-emitting diodes, , photovoltaic devices, − tactile sensors, gas sensors, and PDs. − In particular, combining biomaterials and inorganic materials can create or enhance the optoelectronic functions such as photoresponse or photovoltaic characteristics. − For example, the surface functionalization of biomolecules including fluorescent proteins can provide inorganic materials with the enhanced light absorption via the light-induced charge transfer at the biomaterial/inorganic interface. , In recent years, it has been reported that the incorporation of a biophotosensitizer into IGZO photo-TFTs is able to alleviate the PPC due to the light-induced charge transfer . However, it is still a significant challenge to improve optical absorption accompanying high photoresponsivity and specific detectivity and fast and repeatable photoresponse characteristics caused by suppression of PPC for functional UV PDs based on IGZO photo-TFTs.…”

“…15 Accordingly, substantial efforts have been devoted to enhance the photoresponse characteristics of IGZO photo-TFTs such as the application of a positive-gate bias pulse, 15,22,25 optimization of the metallic component of a thin film, 26 and formation of heterostructures with other materials including perovskites, 27,28 polymers, 14,22 2D TMDCs, 29 and biomaterials. 23 Recently, biomaterial-based electronic devices have been developed due to potential applications including lightemitting diodes, 30,31 photovoltaic devices, 32−34 tactile sensors, 35 gas sensors, 36 and PDs. 36−39 In particular, combining biomaterials and inorganic materials can create or enhance the optoelectronic functions such as photoresponse or photovoltaic characteristics.…”