| In 2004,Ohtomo and Hwang found that LaAlO3/SrTiO3(LAO/STO)interface exhibited two-dimensional electron gas(2DEG)with a high mobility.Later,a variety of exciting physical properties have been reported.Among these,as a powerful external perturbation,light can significantly modulate properties of the interface.Considering the multifunctional coupling effect of the light,electric and magnetic of the oxide system,LAO/STO interfaces are the main research object in this paper.Firstly,LAO films were prepared on STO substrates with different crystal plane orientations by a pulsed laser deposition(PLD)method to study the influence of lattice stress on photoelectric properties.Then,the influence of film thickness and stress gradient on the photoelectric properties of LAO/STO was studied.And photo Hall-effect measurement method was optimized to study the dynamic mechanism of LAO/STO interface.Finally,the effect of doped elements on transport properties was studied.The main work of this paper includes the following aspects:(1)Atomically smooth single-terminated(001),(111)and(110)STO substrates with a step-terrace morphology were obtained using different treatments.Subsequently,a series of LAO films were prepared on STO substrates with different directions at different oxygen pressures,4×10-3?4×10-1 Pa by PLD.The electrical measurement results show that the interface conductivity is senstive to the oxygen pressure,and the interface exhibits an insulated behavior at 4×10-1 Pa.The photoresponsive results of(001),(111)and(110)LAO/STO interfaces are closely related to oxygen pressure.In addition,the interface of(110)shows smaller photoinduced resistance and smaller residual resistance,and the interfaces of(001)and(111)have no significant difference,indicating that the electron reconstruction caused by polarization discontinuous is crucial in the process of photoresponse.These results are of great significance for the study of intrinsic characteristics of oxide 2DEG and have reference value for the design of photoelectric devices.(2)The influences of thickness and buffering layer on photoresponsive characteristics of STO-based oxide heterointerfaces are investigated.In addition to the typical persistent photoconductivity,the transient photoconductivity is observed at the heterointerfaces below the critical thickness.More intriguingly,it shows a transition from the transient photoconductivity to the persistent photoconductivity for the interfaces at the critical thickness with enhancing temperatures.The transition temperatures are 270 K for 1.2 nm LAO/STO and 150 K for 1.2 nm LSAT/STO.Moreover,larger strain at the LAlO/STO interfaces produces a roughly greater photoinduced change in the resistance than the strain-relaxed(La0.3Sr0.7)(Al0.65Ta0.35)O3(LSAT)/STO interfaces.These results are important for intrinsic mechanisms of two-dimensional electron gas at complex oxide interfaces.The effect of LSAT layer on transport and photoresponsive properties at LAO/STO interfaces was investigated.It is interesting that the the critical thickness is increased and the electron mobility is enhanced.For LAO(3.2 nm)/LSAT(0.8 nm)/STO sample,the mobility is enhanced by about two orders of magnitude and the maximum value is about 2059.0 cm2/Vs at 20 K.Moreover,the LSAT layer enriches and improves the photoresponse of LAO/STO interfaces.In particular,an irreversible photoinduced insulator-to-metal transition is achieved at LAO(1.6 nm)/LSAT(0.4 nm)/STO interfaces.(3)The 2 nm LAO/STO interfaces were prepared by PLD.The dynamics of carrier density and mobility under and after light illumination by Hall effect over time were studied.After the illumination,a marginal decrease in n2 and an increase in?2 are observed.The n2plummets from 7.8×1013 cm-2 to 5.0×1013 cm-2 and the?2 is raised from 17.2 cm2/V s to 63.7cm2/V s at 10 K,respectively.It is discovered that the variation of mobility caused by the electron-electron scattering plays an important role in the recovery process in addition to the reduction of carrier density.Furthermore,the gating effect can tune the recovery process after light illumination.The results illuminate the detailed mechanisms of nonequilibrium process and are helpful for the modulation of carrier by light and electric field.(4)The targets of Ni doped LaAl1-xNixO3(x=0,0.01,0.03,0.05)and other elements doped LaAl0.95Y0.05O3(Y=Fe,Co,Ni,Cu)were prepared by a solid phase reaction method.A series of films have been deposited on TiO2-STO and the transport behaviors of LAO/STO heterointerfaces modified through the dopant at Alsite have been investigated.All samples exhibit metallic behavior and,the resistance,carrier density and mobility of interfaces have been modified.Through the Ni dopant,the resistances increase significantly.Under irradiation,the interfaces exhibit a suppressed Kondo effect at low temperature.The relative changes in resistance(?Rp)of interfaces induced by light are increased from 86.1%to 96.9%by increasing the substitution of Ni.More significantly,magnetic-doped samples exhibit obvious magnetic hysteresis loops.This work is helpful for a deep understanding of magnetism and spintronics in oxide 2DEGs. |
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