Design of a photodiode based on NiO/ZnO heterojunction

The recent interest in applications of ultraviolet photodiodes based on Nickel Oxide/ Zinc Oxide (NiO/ZnO) heterojunction heightens the need for more developments. One of the greatest challenges was to indicate which factors control the performance of these devices. Therefore, this research is based on three studies. In the first study, we managed to get the effect of the source solution quantity on structural and optical characteristics of ZnO and NiO thin films grown by spray pyrolysis for the design of NiO/ ZnO photodiodes. We assumed that increasing the film thickness reduces the defects and results in less recombination through higher crystallinity which enhances the photodetection. In the second study, we fabricated a NiO/ZnO junction by spray pyrolysis with optimum conditions. We performed a simulation to clarify the effects of heterojunction behavior and interface trap on the performance of NiO/ZnO photodiodes. The origin of current has been attributed to the tunneling, thermionic emission in the interface and due interface traps SRH generation and recombination controlling the carrier transport at the heterojunction. As a third study, the radio frequency sputtering technique was used to deposit NiO and ZnO thin films to form NiO/ZnO heterojunction in oxygen flow absence conditions. We found that the NiO/ZnO heterojunction has a semi-transparency in the visible range which makes this heterojunction suitable for broadband photodetection applications. This study demonstrates that NiO/ZnO heterojunction could play an important role in many applications such as broadband photodetection (ultraviolet and visible ranges), partial transparent optoelectronic devices and solar cells. These studies imply that using the crystal structure as desired has always been the key to designing and targeting high-quality heterojunctions. These results have allowed us to identify key parameters useful for the optimization of NiO/ZnO photodiodes, as well as to give realistic estimates of the performances of such UV device

Recent Advancements in TiO₂ Nanostructures: Sustainable Synthesis and Gas Sensing

The search for sustainable technology-driven advancements in material synthesis is a new norm, which ensures a low impact on the environment, production cost, and workers’ health. In this context, non-toxic, non-hazardous, and low-cost materials and their synthesis methods are integrated to compete with existing physical and chemical methods. From this perspective, titanium oxide (TiO2) is one of the fascinating materials because of its non-toxicity, biocompatibility, and potential of growing by sustainable methods. Accordingly, TiO2 is extensively used in gas-sensing devices. Yet, many TiO2 nanostructures are still synthesized with a lack of mindfulness of environmental impact and sustainable methods, which results in a serious burden on practical commercialization. This review provides a general outline of the advantages and disadvantages of conventional and sustainable methods of TiO2 preparation. Additionally, a detailed discussion on sustainable growth methods for green synthesis is included. Furthermore, gas-sensing applications and approaches to improve the key functionality of sensors, including response time, recovery time, repeatability, and stability, are discussed in detail in the latter parts of the review. At the end, a concluding discussion is included to provide guidelines for the selection of sustainable synthesis methods and techniques to improve the gas-sensing properties of TiO2