However, the oxide semiconductor has one weakness, a light-induced threshold voltage instability.[18, 19] Despite that, the light-induced instability can be put to good use as the basis of a high-gain photo-image sensor, with higher sensitivity than the amorphous silicon equivalent. We analyze the photo conduction mechanism in oxide semiconductor and use this to maximize the performance of image sensors to provide ultra-high photoconductive gain. Previously, we reported a phototransistor embedded in a display pixel,[20] in which gate operation is used to accelerate recovery from photocurrent level to the dark state. In this work, we describe the origin of ultra-high quantum efficiencies in an all invisible imaging array with photosensors based on nanocrystalline oxide heterojunction thin-film transistor (TFT) where we use well-known oxide materials such as InZnO [21–29] and HfInZnO.[30] While the InZnO is known to have optical transparency it has a significant number of subgap states associated with oxygen vacancies leading to persistent photoconductivity.[21–24] In order to understand the origin of the high photocurrent of a device, we evaluated the influence of a light spot from source to drain side on the photoconductive gain of photosensor array. A three-dimensional device simulation tool was employed. Also, a set of pulse measurement experiments and first-principles calculations based on hybrid density functional theory were performed to study the effect of applying gate bias on the recovery mechanism of photocurrent. Three primary factors are believed to be responsible for the high quantum efficiency. Introducing a buried layer with a higher density of oxygen vacancies (V o), as an integral part of the TFT channel, leads to significant visible-light absorption. This coupled with a favorable band offset along with gate-modulated band bending leads to transfer of photogenerated electrons to the photo-TFT channel where the V o concentration is small. Because of hole localization, recombination is retarded, giving rise to an extended electron lifetime, and hence, high quantum efficiency. In addition, scaling down the channel length of the TFT reduces the carrier transit-time from source to drain, yielding a higher efficiency. This work presented here demonstrates the first invisible, high sensitivity image sensor along with quantitative analysis of the quantum efficiency in the heterojunction TFT taking into account the optical absorption, electron lifetime, and transit time. In order for the photosensor element to meet the requirements of both light sensitivity and manageable dark state device characteristics, a bilayer HfInZnO (HIZO)/[(In 2O 3)-(ZnO)](IZO) active semiconductor was used, as shown

Ever-evolving advances in oxide semiconductor materials and devices [1–5] continue to drive leading-edge developments in transparent electronics,[6–9] thanks to new integration processes, enabling large-area processing on rigid and flexible substrates. In transparent electronics, the key materials are wide bandgap semiconductors, such as oxide semiconductors.[8] This family of semiconductors offer a host of advantages such as low cost and high scalability, in addition to seamless heterogeneous integration with many other inorganic and organic materials in view of their low thermal budget in processing which provides integration flexibility. This has spawned a wealth of applications ranging from high frame-rate interactive displays with embedded imaging to flexible electronics,[10–15] where speed and transparency are essential requirements.[3, 16] Interest in oxide semiconductors stem from a number of attributes primarily their ease of processing, high field …