Dynamics of photo-generated non-equilibrium electronic states in Ar+ ion irradiated SrTiO₃

الأصل · EN

A metallic surface is realized on stoichiometric and insulating (100) SrTiO₃ by Ar+ - ion irradiation. The sheet carrier density and Hall mobility of the layer are 4.0 × 10¹⁴ /cm² and 2 × 10³ cm²/Vs respectively at 15 K for the irradiation dose of 4.2 × 10¹⁸ ions/cm². These samples display ultraviolet light sensitive photoconductivity (PC) which is enhanced abruptly below the temperature (≈100 K) where SrTiO₃ crystal undergoes an antiferrodistortive cubic-to-tetragonal (Oₕ¹ → D₄ₕ¹⁸) structural phase transition. This behaviour of PC maps well with the temperature dependence of dielectric function and electric field induced conductivity. The longevity of the PC-state also shows a distinct change below ≈100 K. At T > 100 K its decay is thermally activated with energy barrier of ≈36 meV, whereas at T < 100 K it becomes independent of temperature. We have examined the effect of electrostatic gating on the lifetime of the PC state. One non-trivial result is the ambient temperature quenching of the photo-conducting state by the negative gate field. This observation opens avenues for designing a solid state photo-electric switch. The origin and lifetime of the PC-state are understood in the light of field effect induced band bending, defect dynamics and thermal relaxation processes.