Preparation And Physical Properties Of La-and V-Doped SrSnO₃ Epitaxial Films

Strontium stannate(SrSnO₃)with perovskite structure,as a wide bandgap material,has the characteristics of low electron effective mass and high carrier mobility,and has attracted widespread attention in recent years.In this paper,a series of SrSnO₃thin films were epitaxially fabricated on lanthanum aluminate(La Al O₃)single-crystal substrates by pulsed laser deposition technique,and using La and V elements as the main cationic dopants,the crystal structure,optical,electrical and magnetic properties were investigated.Systematically study combined the first-principles calculations to corroborate the reliability of experiments.The main research work of this paper is divided into the following three aspects:(1)The structure and nonlinear bandgap control of V-doped SrSnO₃ epitaxial films.Using V as a cationic dopant,Sr Sn_1-xV_xO₃ films(SSVO,x=0,0.25,0.5,0.75 and 1)were fabricated on single-crystal La Al O₃ substrates by laser deposition technique.The influence of V doping concentration on the crystal structure and band structure of SrSnO₃ thin films were studied combined with first-principles calculations.The results showed that SSVO films were successfully epitaxially grown on single-crystal La Al O₃substrates,and the lattice parameters gradually decreased with increasing V concentration.The optical bandgap values of the SSVO films exhibited a nonlinear variation,the value initially increased from 4.43 to 4.56 e V,while further increasing the V doping content,the bandgap value decreased to 3.31 e V.Combined with density functional theory calculations,it was revealed that the initial increase in the bandgap of SSVO films was attributed to the hybridization betweenSn5s and V 3d orbitals,and the contribution ofSn5s orbital to conduction band gradually decreased with the increase of V content,while the contribution of V 3d orbital gradually increased.(2)The electrical transport and optical properties of La-and V-doped SrSnO₃epitaxial films.Using La and V as doping elements,(La_0.05Sr_0.95)(Sn_1-xV_x)O₃ films(LSSVO,x=0,0.25,0.5,0.75 and 1)were epitaxially prepared on single-crystal La Al O₃substrates via pulsed laser deposition technique,and the effects of La and V doping on the electrical and optical properties of LSSVO thin films were investigated.The results showed that the room-temperature resistivity of the LSSVO films firstly increased and then decreased with the increase in V doping concentration,the room-temperature resistivity of the LSSVO film at x=1 was the lowest,which was 0.05 m?cm,and the corresponding carrier density value was 1.79×10²² cm^-3.Meanwhile,the metal-semiconductor transition behavior was found in the(La_0.05Sr_0.95)VO₃ film,and the transition temperature was about 49 K.The resistivity of the LSSVO films of other components decreased with the decrease in the test temperature,and the temperature-dependent electrical transport properties could be explained by the QCC mechanism.In the mid-far infrared region,the transmittance of the films decreased with increasing doping concentration.In the near infrared region,the bandgap values of the films increased first and then decreased,and the values were 4.13,4.24,3.98,3.89 and 3.22e V,respectively.(3)Room-temperature ferromagnetism of V low-doped SrSnO₃ epitaxial films.Sr Sn_1-xV_xO₃ films(SSVO,x=0,0.05,0.1,0.15 and 0.25)were grown by pulsed laser deposition technique,and the effects of V low doping on the structure and room-temperature ferromagnetism of the films were investigated.The results showed that both the SSVO films and the La Al O₃ substrates had quadruple symmetrical peaks with an interval of 90°.As V doping increased,the unit cell parameters and volumes of the films gradually decreased.At room temperature,the SSVO films exhibited ferromagnetic behavior in the range of V doping content from x=0.05 to 0.15,and the saturation magnetization could reach 9.59 emu/cm~3,while the saturation magnetization of the film greatly reduced when the V concentration at x=0.25,indicating that the ferromagnetic behavior of the SSVO films depended on the V doping concentration.Meanwhile,it was found that the saturation magnetization of the Sr Sn_0.85V_0.15O₃ film after vacuum annealing achieved a saturation magnetization of 10.80 emu/cm~3.Compared with Sr Sn_0.85V_0.15O₃ film,(La_0.05Sr_0.95)(Sn_0.85V_0.15)O₃ film had higher saturation magnetization at room temperature.