Multifunctionality of Giant and Long-Lasting Persistent Photoconductivity: Semiconductor–Conductor Transition in Graphene Nanosheets and Amorphous InGaZnO Hybrids

Abstract

Composite materials can play a decisive role to reveal novel physical properties and enable to advance new generation technologies. Here, we discover that phototransistors based on the integration of two-dimensional graphene nanosheets (GNSs) and amorphous indium− gallium−zinc−oxide (a-IGZO) semiconductors exhibit a giant photo-to-dark current ratio and long-lasting persistent photoconductivity (PPC). Under the illumination of UV light (350 nm) at 50 mW/cm 2 , a photo-to-dark current ratio up to 2.0 × 10 7 was obtained, which is about 3 orders of magnitude higher than its pure a-IGZO device counterpart. Moreover, the GNSs/a-IGZO phototransistor possesses an enduring lifetime up to years for the recovery of the transfer characteristics after switching off the UV light. The giant and long-lasting PPC leads GNSs/a-IGZO to become an excellent conductor with conductivity much better than indium tin oxide. The observed unique features represent a semiconductor−conductor transition. In addition to next generation flat, flexible, and display, it can open up a wide variety of application, such as transparent electrodes for optoelectronic devices, optical memory, and light harvesting for energy storage. As an example, we demonstrated the operation of optical memory devices, which may lead to the novel application of holographic storage. Our results shown here therefore provide an outstanding new route for the future development of solution-processable semiconducting optoelectronic devices. D ue to the coupling among constituent materials, hybrid composites enable to possess exceptional properties and multifunctionality, which cannot be found in single component. As a result, their applications can be expanded to a wide range of fields. Recently, amorphous oxide semiconductor (AOS) have created a new area of electronics and optoelectronic devices. 1,2 Among the various AOS types, amorphous indium− gallium−zinc oxide (a-IGZO) thin-film transistors (TFTs) have been considered to be one of the most promising candidates for next-generation flat, flexible, and transparent display devices, mainly owing to their high electron mobility, optical transparency, chemical stability, and processing versatility. 3,4 Replacing TFTs made of hydrogenated amorphous silicon (aSi: H) with transparent a-IGZO TFTs can significantly boost the aperture ratio of pixels, reduce the power, and simplify device fabrication. 5,6 For system-on-panel (SoP) applications, IGZO-based nonvolatile memory (NVM) is required, and many research teams are actively pursuing related devices. 7−9 Besides, the IGZO-based TFTs have been utilized in phototransistors and photosensors due to their high sensitivity to light, mobility, and on/off ratio for integrated circuits. 10,11 With the additional terminal, light memory devices based on IGZO and AOS phototransistor can be realized with the special optical programming and electrical erasing processes. 12,13 To ensure the application in nonvolatile memories such as flash memory, a long retention time is one of the most imp...

The self-activated radical doping effects on the catalyzed surface of amorphous metal oxide films

“…In this respect, the strong oxidizer, which is a hydroxyl radical, can preferentially react with oxygen defects without prolonged treatment and an additional energy source. The hydroxyl radical (OH*) obtained from the decomposition of hydrogen peroxide (H 2 O 2 ), is generally used to eliminate organic components in the solution process due to its high oxidation potential compared to oxygen and ozone 14–16 . According to the previous reports, the H 2 O 2 is decomposed to OH* by photolysis 17 , pyrolysis 18 , catalytic pyrolysis, and catalysis on the surface of the metal oxide particle 19,20 .…”

“…In addition, the UV irradiation can also lead to the transition of V 0 to V 0 2+ states as releasing the free electrons in the oxide films and this V 0 2+ tends to get back to the ground state after a certain amount of time 22 . Normally, these metastable defects cause persistent photoconductivity (PPC) and negative bias-illumination stress (NBIS) degradation in most of the AOSs 22,23 . In this respect, these metastable oxygen defects can easily react with OH*.…”

Precise Patterning of Large‐Scale TFT Arrays Based on Solution‐Processed Oxide Semiconductors: A Comparative Study of Additive and Subtractive Approaches

“…Because some of the states become upper than the quasiFermi levels, these states become more possible to be unoccupied, i.e., electrons trapped in these states will be released to the conduction levels. Besides, the band gap of the IGZO/IZO films is over 3.0 eV, and so the carriers from the deep states may also be excited to the conduction levels by the absorption below 400 nm under the illumination . Consequently, the overall mobile carrier number increases and V TH shifts toward negative.…”

“…Metal oxide‐based thin film transistors (TFTs) have demonstrated considerable potentials for applications in sensors, solar cells, nonvolatile memory devices, and flat panel displays in ultrahigh resolution . Compared with amorphous silicon and organic semiconductors, metal oxide semiconductors (MOS) exhibit the advantages of high electron mobility (more than 10 cm 2 V −1 s −1 ), high transparency, and large‐area uniformity . In general, indium (In) and tin (Sn) elements are often employed as the key components in high mobility compounds for their heavy metal cations with ( n − 1)d 10 n s 0 electronic configurations, which provide fast conduction pathways for the free carriers .…”

“…For the films that are grown by vacuum‐assisted techniques, such as sputtering or pulsed laser material ablation, the element stoichiometric ratio needs to be critically controlled by considering the different evaporation rates of target materials . To realize cost‐effective, large‐scale, and high throughput fabrication, solution‐based techniques (usually based on sol–gels) have also attracted significant interests, including spin‐coating, spray pyrolysis, bar‐coating, etc. The main problems for solution‐based techniques include the relatively high annealing temperature (>400 °C), the instability under various bias‐stressing, and effective patterning .…”