Influence of carrier mobility on sensitivity of room-temperature-operation CO₂ sensor based on SnO₂ thin film

Abstract

CO2 sensors capable of operating at room temperature were fabricated using LaOCl/SnO2 thin films. The carrier mobility of the SnO2 layer was increased by H2 ambient annealing, during which the O vacancies in SnO2 were passivated by H atoms. The sensitivity of the CO2 sensors was strongly affected by the mobility of the SnO2 layer because of the large diffusion length of carriers. By using the SnO2 layer with a carrier mobility of 10.6 cm2 V−1 s−1, a highly sensitive CO2 sensor with a detection limit of 1000 ppm was obtained. The sensor was visible-light-transparent and the transmittance in the visible region was over 70%.

Polycrystalline SnO2 Visible‐Light‐Transparent CO2 Sensor Integrated with NiO/ZnO Solar Cell for Self‐Powered Devices

“…As such, CO 2 sensor‐based oxide semiconductors are typically heated during measurement. However, the mobility of the charge carriers in the SnO 2 film in our CO 2 sensor was higher than that of other semiconductors commonly used in CO 2 sensors . Hence, our CO 2 sensor can operate at room temperature and can presumably be employed in greenhouses and indoor spaces such as offices and houses, particularly because quick CO 2 response is not required in such applications.…”

“…This may be due to the poor film quality, particularly in terms of its surface flatness and uniformity. In fact, the single CO 2 sensor, which was fabricated directly on a flat glass substrate, responded to a variety of CO 2 concentrations . In contrast, the integrated sensor device was fabricated on SiO 2 /NiO/ZnO/ZnO:H/ITiO‐stacked layers on the same glass substrate.…”

“…For the insulating layer shown in Figure (b) and (c), SiO 2 thin films were deposited on the solar cell layer by electron beam evaporation. Finally, for the CO 2 sensor layer fabrication, polycrystalline SnO 2 thin films with a thickness of 50 nm were deposited on the insulating layer by RF sputtering method without intentional heating, as shown in Figure (d) . An La‐related catalyst solution, namely methanol, was used to dissolve LaCl 3 · 7H 2 O to obtain an La concentration of 100 mmol m −3 ; the solution was spin coated on the surface of the SnO 2 thin films.…”

“…A representative surface view of the integrated self‐powered device is shown in Figure (e). The electrode of the sensor comprises eight fingers; each finger is 1.3 mm long, and the finger–finger spacing is 100 μm …”

“…In our previous report, SnO 2 -based "invisible" CO 2 sensors operating at room temperature were fabricated. [24] Using an SnO 2 layer with a mobility of 10.6 cm 2 V À1 s À1 , we fabricated a highly sensitive CO 2 sensor with a detection limit of 1000 ppm. The sensor is visible-light transparent, and the optical transmittance in the visible region is over 70%.…”