Gas sensing properties of <i>c</i>-axis-oriented Al-incorporated ZnO films epitaxially grown on (11-20) sapphire substrates using pulsed laser deposition

Abstract

Al-incorporated ZnO films with various Al concentrations were prepared using pulsed laser deposition on the (11 20) face of sapphire substrates, and their gas sensing properties were evaluated. The use of c-axis-oriented epitaxial films with the same thickness suppressed the influence of the surface-to-volume ratio and surface atomic arrangements on the sensing properties, clarifying the role of Al doping in the improvement of ZnO gas sensors. The results of ethanol gas sensing measurements indicated that Al doping significantly improved the sensing response and response time of the ZnO gas sensors. The formation of Al-related impurity phases and/or non-equilibrium defects induced by Al doping improved the sensing performance. On the other hand, changes in the grain size did not significantly affect the sensing response.

Highly Sensitive Ethanol Gas Sensor Using Pyramid-Shaped ZnO Particles with (0001) Basal Plane

“…A high sensing response was obtained at 310–350 °C. This agrees with the suitable operating temperature range of 250–400 °C for ethanol sensors using ZnO. − As shown in Figure , more time was needed to maintain a constant resistance in ethanol gas at lower temperatures, where the oxidation reaction of ethanol molecules on the ZnO surface is slower compared to that at higher temperatures. At higher temperatures, the sensor response value decreased due to desorption of ethanol.…”

“…It is also widely used in electronic applications, such as varistors, surface acoustic wave filters, transparent electrodes, and phosphors . Control of the morphology of ZnO nanostructures has been intensively investigated, and a wide variety of morphologies (e.g., nanowires, rods, plates, flowers, rings, and spheres) have been observed for particles and thin films. , Various ZnO nanostructures have been studied for gas sensor applications. − In our research, we found that the best result for ZnO ethanol sensors was brought by nanoparticles of about 15 nm synthesized via a vapor phase method . The sensor response (ratio of electrical resistance in air to that in ethanol gas) to 50 ppm ethanol gas in air was about 500 at 400 °C.…”

Ethanol Gas Sensing by a Zn-Terminated ZnO(0001) Bulk Single-Crystalline Substrate

“…It is worthwhile to note that the ZnO sample exhibits a large S of 21 with an R air saturate of about 6 GΩ. It is a surprisingly large sensitivity by considering that the ZnO single-crystalline thin film with a thickness of several tens of nanometers has an S of 10–20 ( Figure S1 and refs ( 22 ) and ( 37 )). The relationship between S and R air saturate in Figure 2 c indicates that S may further increase with the increase of R air saturate .…”

“…The details of the apparatus have been described elsewhere. 37 Briefly, the apparatus has essentially the same design as that for evaluating gas sensing properties by the conventional two-terminal method.…”

“…The EtOH (50 ppmv) sensing sensitivity by a crystalline ZnO thin film with a thickness comparable to the space charge layer thickness (several tens of nanometers) has been reported to be in the range of 10–20 (Figure and refs and ). By taking this value into account with a space charge layer thickness of 400 nm for the single-crystalline substrate, the EtOH sensing sensitivity is estimated to be smaller than 10 –2 on a ZnO bulk crystalline substrate with a thickness of 1 mm.…”