Gas Sensing Properties Of SnO₂-oriented Semiconductor Films Based On Oxygen Regulation

Tin dioxide?SnO₂?based nanomaterials are one of the most common N-type semiconductors,and plymorphic SnO₂ exhibit different physicochemical properties.SnO₂ material is not only used in transparent conductive electrodes,solar cells,lithium-ion batteries and other fields,but also widely used in the detection of various gases due to its high sensitivity,strong selectivity,fast response/recovery,good chemical stability.In this work,magnetron sputtering with a radio frequency powder target was used to prepare the tin dioxide based films with different preferred orientations by controlling the sputtering gas atmosphere at room temperature,and then the annealing process in different atmospheres further regulates the microstructure of the films to explore the gas sensing properties unique to the SnO₂-based material.The microstructure,surface morphology and gas sensing properties of the films were characterized by X-ray diffractometry,Raman spectroscopy,Photoluminescence spectroscopy,Atomic force microscopy?AFM?,Scanning electron microscopy?SEM?,Hall Effect and electrochemical workstation.The studied results are as follows:?1?A tetragonal rutile SnO₂ film with?101?and?110?preferred orientation was prepared under the oxygen-free and oxygen-containing Ar atmosphere,respectively.The polar unsaturated oxygen-poor film with?101?preferred orientation has a large surface free energy and a narrow doped band gap,and the non-polar saturated oxygen-rich film with?110?preferred orientation has a smaller grain size and more large surface roughness.After vacuum annealing at 400 °C,the preferred orientation of the films did not change,the surface of films is more even and smooth,and the tip of the crystal column changed to a hemispherical to decrease the surface energy.?2?Compared with?101?preferred orientation SnO₂ film,?110?-oriented SnO₂ film has more adsorption sites,higher H2 response of R=9.6,and better selectivity for H2?CO is a interfering gas?of S=6.5,but its optimal response temperature is slightly higher.After vacuum annealing,the response of both oriented films decreased with the loss of lattice oxygen,indicating the important influence of lattice oxygen on the gas sensitivity of the film.?3?Compared with?110?preferred orientation SnO₂ film,?101?-oriented SnO₂ film has better photoelectrolytic water characteristics.The atomic step on the grain surface is the active site of photoelectrolytic water,while the lattice atom including O_bridging is the main site of gas-sensitive performance.The H2 response of the two oriented films under nitrogen carrier gas is higher than that under air carrier gas,further indicating that lattice oxygen is the dominant factor in the gas sensitivity of magnetron sputtering SnO₂ films.?4?Through sputtering fluorine doping and annealing oxygen management,a wide range of carrier concentration and mobility of SnO₂ films with a single?101?preferred orientation were regulated,and the carrier concentration varied from 10¹⁵ /cm³ to 10²¹ /cm³,which proved that the gas response of film was mainly controlled by carrier concentration.The film with a minimum carrier concentration of 10¹⁵ /cm³ have a higher gas responsivity R=5.0,while the film with a highest carrier concentration of 10²¹ /cm³ have the shortest response and recovery time.When carrier concentration is the same,the mobility also has a secondary effect,and low mobility can promote the gas-sensitive response to some extent.