Spray deposited Mg-doped SnO₂ thin film LPG sensor: XPS and EDX analysis in relation to deposition temperature and doping

Highlights: • Mg doped SnO₂ thin film significantly improves the LPG response to 93%. • Mg doping concentration up to 0.9 wt% is helpful in decreasing the grain size. • The O/Sn ratio supports excess oxygen in films whereas XPS suggests dissimilar chemical states. • Doping leads to an enhanced oxygen adsorption by a favourable crystallite orientation. • Adsorbed oxygen ions responsible for enhanced response can be perceived at the grain boundaries or at the surface, on account of the absence in the crystalline matrix. - Abstract: Magnesium doped SnO₂ polycrystalline thin films are deposited by Spray pyrolysis by adding small amount of Mg between 0.3 and 1.2 wt%. Mg doping significantly modifies the gas sensing properties of tin oxide thin films by yielding (1 1 0) and (1 0 1) crystallite orientation to accommodate oxygen vacancies which lead to enhanced oxygen adsorption. A correlation is established between the crystallite orientation and the gas sensing magnitude by plotting the texture coefficient. The structure, surface chemical composition, and the optical and electrical properties are studied in relation to the gas sensing magnitude. It is shown that the magnesium doping in SnO₂ maintains tetragonal rutile structure in stable cassiterite phase over low doping concentrations. The grain dimensions are influenced by both doping concentration and substrate temperature. Electronic surface states identified by the XPS are deconvoluted to establish the constituent oxygen states, while the EDX compositional analysis indicates added oxygen adsorption. As the temperature is raised for the response measurement, the adsorbed oxygen may transform to O⁻ or O²⁻ which is supported by the increase of film resistance. It is shown that the sensor response to LPG is improved significantly (93%) by the addition of minor amounts of Mg to SnO₂ thin film sensors