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Al-doped TiO2 (ATO) interfacial layer improves the charge balance and the performance of quantum-dot light-emitting diodes (QLEDs).

Vanadium oxide (V2O5) doped with Li (5, 10, and 15 mol%) was synthesized using an easy and low-cost solution process method and was used as a hole-injection layer (HIL) for quantum-dot light-emitting diodes (QLEDs).

A visible-light phototransistor have been fabricated by adding a solution-processed thin Al2O3 layer under the ZnO layer to improve the visible-light photodetection.

The wide band gap of oxide semiconductors enables them to generate photocurrents through irradiation with high-energy photons, such as by ultraviolet light. To enhance the photoresponsivity of an oxide semiconductor to visible light, we fabricate a phototransistor by doping ZnO with Li. The amount of oxygen vacancies in ZnO is controlled by changing the concentration of lithium hydroxide in ZnO solution. Li dopants increase the electron concentration in ZnO, thereby improving the electrical behavior of ZnO thin-film transistors (TFTs). The Li-doped ZnO TFTs exhibit a high field-effect mobility of 10.15 cm2 V−1 s−1 and a high on/off ratio of ∼107. These oxygen vacancy states are located above the valence band of ZnO; therefore, they can generate a photocurrent upon irradiation of Li-doped ZnO TFTs with visible light. Li-Doped ZnO phototransistors exhibit excellent photodetection characteristics (photoresponsivity: 23.11 A W−1; photosensitivity: 4.94 × 106) upon 520 nm laser irradiation on the device, when the concentration of lithium hydroxide is 5 mol%. In addition, Li doped ZnO TFTs can be operated stably without light-induced aging effects or degradation caused by negative bias stress. Ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy measurements are performed to investigate the origin of the improved visible-light photoresponsivity of the Li-doped ZnO phototransistors. Our experimental results suggest that a visible-light photodetector can be developed using wide band gap ZnO.

We have developed a visible-light phototransistor with excellent photodetection characteristics and stability via atomic layer deposition (ALD) to add a thin layer of aluminum oxide (Al2O3) to quantum dot (QD)/zinc oxide (ZnO) films. Al2O3 was used to passivate the surface of the QDs and fill the interspace of the QDs. This led to a reduction in the number of QD surface traps and prevented damage due to the migration of aggressive metal atoms during electrode deposition. Additionally, some parts of Al2O3 deposited on the surface of ZnO triggered a doping effect by interacting with ZnO. This enhanced the electrical properties of ZnO TFTs by providing an extra electron and allowed the efficient transfer of photoelectrons from the QDs to ZnO by reducing the conduction band minimum of ZnO. Therefore, upon 520 nm laser irradiation Al2O3/QD/ZnO TFTs exhibited excellent photodetection characteristics (e.g., photosensitivity: 3.8 × 107, photoresponsivity: 46.8 A W−1, and photodetectivity: 4.5 × 1014 Jones) at a gate voltage of −5 V. Excellent electrical properties, such as saturation mobility of 1.72 cm V−1 s−1 and on/off current ratio of 1.8 × 106, were also realized. Furthermore, the photo-excited charge transfer mechanism was investigated using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and time-resolved photoluminescence. Our experimental results suggest a method for realizing enhanced optoelectronic characteristics and stability of QD/ZnO TFTs via ALD-Al2O3 deposition, which is useful for developing high-performance visible phototransistors.

Conventional visible-light phototransistors based on the heterostructure of wide band gap zinc oxide (ZnO) and colloidal quantum dots (CdSe/ZnS QDs) have been studied. However, it is found that there are various deteriorated characteristics for their photoelectric behavior. Here, the phototransistors of an additional thin layer of TiO2 deposited onto the ZnO/QDs film using atomic layer deposition are developed for improving the performance of phototransistors. Small band gap QDs can absorb low-energy visible light and generate photoexcited charge carriers, which can be injected into the conduction band of wide band gap ZnO. Subsequently, the photoexcited charge carriers can be injected into the conduction band of TiO2 owing to the low injection barrier. Therefore, the ZnO/QDs phototransistor with the TiO2 layer can generate a larger photocurrent from visible light compared to a device without the TiO2 top layer. Moreover, the inorganic TiO2 layer improved the stability of the device. Under illumination with light at a wavelength of 520 nm, the maximum photosensitivity of the device was 4.2 × 106 and the transition rate was 0.728 ns−1, which is high enough to reduce the persistent photocurrent effect. This work offers a useful method to enhance the performance of visible-light phototransistors based on a heterostructure of oxide semiconductors and QDs.