Study On Photoelectric Properties Of SnO₂ Regulated By Doping

SnO₂,as a direct wide-bandgap oxide semiconductor with electron carrier（n-type）conduction,has excellent optoelectronic properties and is widely used in solar cells,catalytic materials,transparent electrodes,and solid-state chemical sensors.To meet the requirements of the optoelectronic performance of SnO₂ in various applications,single metal ion doping methods were used to modulate the optical and electrical performance of SnO₂.However,single metal ion doping can be limited to modulating the optical and electrical performance of SnO₂.In this thesis,the effect of two different valence metal ions co-doping on the optoelectronic properties of SnO₂ was investigated by combining the first-principles calculations and experiments.The specific research content is as follows,1.The electronic structure and defect formation energy of Ca（and Ga）-doped SnO₂ were calculated using first principles based on density functional theory.The calculation results suggest that Ca _Sn(Ga _Sn)and Ca _Sn-V_O(Ga _Sn-V_O)complex defects have low formation energy,and the Ca（Ga）acceptor impurity will compensate for the electrons in SnO₂,resulting in a decrease in electron concentration.In the experiment,Ca（and Ga）-doped SnO₂ thin films were prepared by the sol-gel method combined with post-annealing treatment.The experimental results indicate that the incorporation of Ca impurities in SnO₂can make the lattice of SnO₂ expand,while Ga impurities can make the lattice shrink to some extent.The optical band gap of SnO₂ thin film decreases with the addition of Ca and Ga,which is consistent with the theoretical calculation results.In addition,we also designed and fabricated photodetectors based on Ca-doped and Ga-doped SnO₂ films.The responsivity measurements indicate that the responsivity of Ga-doped SnO₂ photodetectors is enhanced by about 2.6 times compared with undoped SnO₂ photodetectors,while no obvious optical response was observed for the Ca-doped SnO₂ photodetectors.2.Density functional theory is used to calculate the defect formation energy,optical absorption,and density of states for Ga-Ca co-doped SnO₂.It is found that the formation energy of Ga _Sn-V_O and Ca _Sn-V_O in the co-doped SnO₂ system is lower than that of V_O in undoped SnO₂.The Ga-Ca co-doped SnO₂ thin films were prepared by the sol-gel method combined with post-annealing treatment.The photodetectors based on Ga-Ga co-doped SnO₂ thin films were designed and fabricated.With the increase of the doping concentration,the ultraviolet responsivity of the devices increased gradually.The best responsivity for the photodetectors based on co-doped SnO₂ film was comparable to that of the undoped devices,but the detective was improved by orders of magnitude compared with that of Ga-doped devices.The photodetector based on the co-doped SnO₂ shows a lower dark current.