Growth and Characterization of Sputtered ZnO:ZnGa₂O₄ Dual-Phase Films on Sapphire Substrates for NO Gas-Sensing Applications

Abstract

Nitric oxide (NO) released from combustion facilities and automobiles adversely affects the respiratory systems and environment. Hence, the development of a NO gas sensor with high sensing response to measure NO gas levels is significantly commendable. Herein, we report the growth of ZnO:ZnGa2O4 dual-phase films on the c-plane sapphire substrates using radio-frequency magnetron sputtering for NO gas sensors. The microstructures and morphology of ZnO:ZnGa2O4 films were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy. The XRD patterns revealed the polycrystalline nature of the ZnO:ZnGa2O4 film with (222) preferred orientation. The SEM micrographs showed the presence of grain boundaries in the nanostructures over the surface of the film due to the recrystallization of grains upon annealing the film at 700 °C. This ZnO:ZnGa2O4 film was employed to fabricate the NO gas sensor, which demonstrates significantly high sensor response of 28.6 at 400 °C operating temperature with the quick response time of 8 s and recovery time of 140 s upon exposure to 100 ppm NO gas concentration. The ZnO:ZnGa2O4-based gas sensor is found to be highly selective for NO gas among NO, CO2, and SO2 gases. The gas-sensing mechanism behind the high response of ZnGa2O4-based NO gas sensors is described. The results achieved in this study are particularly important in terms of the development of technologies for the early detection of poisonous and hazardous gases from polluting industries and metropolises, which is crucial for environmental security.

Performance Enhancement of ZnGa2O4 Metal Oxide-Semiconductor Field-Effect Transistors Grown via Metal Organic Chemical Vapor Deposition on Sapphire Substrates

“…ZnGa 2 O 4 films (100 nm thickness) were deposited on sapphire substrates via the MOCVD technique, utilizing organic-metal sources and oxygen as the film deposition sources. For this study, the zinc atoms were sourced from diethylzinc (DEZn) with a flow rate of 72 sccm, while the gallium atoms were sourced from triethylgallium (TEGa) with increasing flow rates of 25,30,35,40, and 45 sccm. Argon gas was used as the carrier gas to transport DEZn and TEGa into the reactor.…”

“…Variations in the TEGa flow rates can lead to changes in the film’s stoichiometry, crystal structure, and defect density, thereby influencing charge transport and overall device behavior. , Therefore, the deposition of high-quality ZnGa 2 O 4 films using an efficient technique is of utmost importance. To achieve this, researchers have been actively exploring the optimal growth conditions to achieve the desired electrical and optical properties using radio frequency (RF) magnetron sputtering, pulsed laser techniques, and metal organic chemical vapor deposition (MOCVD) systems. − Since the ZnGa 2 O 4 films deposited using RF magnetron sputtering and pulsed laser techniques have shown polycrystalline behavior on sapphire substrates, , therefore, we have employed the MOCVD system, which is a sophisticated technique to achieve high-quality single-crystalline films, particularly for applications in semiconductor devices. Besides, the sapphire substrates have been taken into consideration in this work due to their low lattice mismatch, high-crystalline nature, and excellent stability with ZnGa 2 O 4 films. , …”

Growth and Performance Enhancement of Sputtered ZnGa2O4 MOSFETs on Sapphire Substrates

“…The ZnGa 2 O 4 spinel exhibits cubic symmetry with the Fd 3̅ m space group, where oxygen atoms are densely packed in a cubic arrangement and cation atoms are arranged in a face-centered cubic pattern. Although ZnGa 2 O 4 possesses a wide band gap and has the capacity to absorb deep ultraviolet (<280 nm) light, exhibiting its potential for applications in deep ultraviolet light sensors, flame detection, ozone layer monitoring, and optical communication, ,− its transistor characteristics remain unexplored. The ample band gap of the ZnGa 2 O 4 material endows it with the capability to withstand high breakdown voltages, showcasing outstanding chemical and thermal stability.…”

Room-Temperature Nitric Oxide Gas Sensors Based on NiO/SnO2 Heterostructures

“…It is responsible for a number of human diseases, such as irritation to the skin or eyes and respiratory malfunctions, such as asthma, etc. [1,2]. Specifically, NO acts as a biomarker for asthma detection because its production by airway cells is strongly related to diseased cells.…”

“…In order to meet the above-mentioned requirements, a great number of materials have been tested as sensing elements against NO gas and using various sensing techniques, such as looking for a change in electrical resistance (chemoresistive sensor) [7], optical sensors [8] or surface acoustic wave devices [9,10]. Among them, chemoresistive sensors are by far the most investigated due to the simplicity of the measurement as well as the great variety of materials that can be used in this technique; however, most of them require a high operating temperature [1,2,[11][12][13][14] or UV irradiation [15][16][17] in order to detect NO gas concentrations below the TLV, leading to extra energy consumption. Thus, only a few works have been reported on NO detection at room temperature.…”