Band Gap Engineering And Physical Properties Of Perovskite SrSnO₃ Thin Films

Band gap engineering is considered as a powerful technology in designing new functionality and meeting the needs of semiconductor device applications.Perovskite structure stannate?ASnO₃??A=Sr,Ba,Ca?is a new type of wide band gap semiconductor with a band gap of about 3.0⁴.5 eV.Especially,SrSnO₃ has been extensively studied due to its excellent physical properties,i.e.high carrier mobility,thermal stability and light transmittance.Yet its large,flexible and adjustable band gap enables it to be a good candidate in optoelectronic device applications.In this paper,band gap engineering of SrSnO₃ films prepared by pulsed laser deposition technique was studied.The effects of oxygen vacancies,La and Pb ions doping and strain on the structure,band gaps and physical properties were discussed.What's more,the reliability of the experiments was confirmed by the first-principle calculations.This paper mainly carries out the following three aspects:?1?Band gap engineering and room temperature ferromagnetism by oxygen vacancies in SrSnO₃ epitaxial film.SrSnO₃ epitaxial film was successfully deposited on a?001?-oriented LaAlO₃ single crystal substrate by adjusting the deposited oxygen pressure employing pulsed laser deposition technique.The effects of oxygen vacancies on the structural,optical and magnetic properties of SrSnO₃ films were systematically investigated.The results show that the unit-cell volume and oxygen vacancy concentration of the film increase gradually with the decrease of deposited oxygen pressure.The transmittance of the film is about 75%in the visible wavelength range and the band-gap value increases gradually from 4.56 to 5.21 eV.Meanwhile,room temperature ferromagnetism is observed in the film,and the saturation magnetization increases from 4.46 to 7.69 emu/cm³ with the decrease of the deposited oxygen pressure.An explanation of band gap modulation and magnetic origin induced by oxygen vacancies in SrSnO₃ was given by theoretical calculations.?2?Effect of La and Pb doping on the band gap and electrical properties of SrSnO₃ epitaxial films.The effects of La and Pb doping on the microstructural,optical and electrical properties of SrSnO₃ epitaxial films were investigated by pulsed laser deposition.The results show that the in-plane lattice constant of SrSn_1-xPb_xO₃?x=0-1,SSPO?film increases from 4.053 to 4.178?with the increase of Pb doping content and the optical band gap decreases from 4.43 to 2.16 eV,while maintaining high transmittance in the visible wavelength range.Theoretical calculations revealed that the reduction in the band energy of Pb-doped SrSnO₃ is due to the overlapping of the Pb 6s and Sn 5s orbits around the bottom of the conduction band.Meanwhile,the electrical properties of the SSPO film doped with 5%La were also studied.The results show that the film at x=1 has the lowest room temperature resistivity(5?10^-4?×cm)and the largest mobility?39.9 cm²/V×s?.?3?Effect of strain on the band gap modulation of SrSnO₃ epitaxial film.SrSnO₃ epitaxial films with different thicknesses?8.5-340 nm?were successfully grown on?001?-oriented LaAlO₃ and MgO substrates by pulsed laser deposition.The effects of strains on the structure and band gap of the film were experimentally investigated combining with density functional theory simulation method.The results show that in-plane biaxial compressive and tensile strains increase gradually for SrSnO₃ films on LaAlO₃ and MgO substrates with decreasing the film thickness.As the in-plane compressive or tensile strains increasing,the band gap of the film grown on LaAlO₃ substrate increases from 4.44 to 5.59 eV while increases from 4.57to 5.61 eV on MgO substrate.More oxygen vacancies are generated in the film as the in-plane tensile strain increasing.An explanation for band gap modulation caused by strain was demonstrated by theoretical calculation.