Electrical Transport Properties Of MgZnO/ZnO And Al₂O₃/SrTiO₃ Heterojunctions

The discovery of two-dimensional electron gas(2DEG)at the interface of oxide heterojunctions,such as MgZnO/ZnO and Al₂O₃/SrTiO₃ heterojunctions,provides a new possibility for the preparation of high electron mobility transistors(HEMT),high-temperature,high-frequency or high-power devices,semiconductor lasers and so on.Transparent conductive oxide(TCO)films,for example SnO₂ films,are widely used in flat panel display,touch screen,solar cell,transparent window,thermal reflection film,electromagnetic shielding window and so on.In this paper,the electrical transport properties of MgZnO/ZnO heterojunctions,Al₂O₃/SrTiO₃ heterojunctions and SnO₂ thin films have been studied.Firstly,the MgZnO/ZnO heterojunctions were successfully prepared by rf-magnetron sputtering at room temperature,the electrical transport properties of which have been studied.The results of Hall measurement indicate that our samples are degenerate semiconductors.At the external vertical magnetic field,the magnetoresistance transition from positive to negative with the incressing temperature is observed in all samples,and negative magnetoresistance still exists at 300 K,which can be well fitted by the two-dimensional weak localization(WL)theory and the two-band model.The temperature dependence of the electron dephasing lengthL?? T-0.5 indicates that the dephasing mechanism of the system is dominated by the electron-electron scattering.Then,the Al₂O₃/SrTiO₃ heterojunctions were successfully prepared by rf-magnetron sputtering at different temperatures,the electrical transport properties of which have been studied.Rs as a function of T exhibits a typical metallic behavior.The 2DEG with high mobility(105 cm2/Vs)is obtained,and a large linear magnetoresistance exceeding 1,100%is observed,which can be attributed to the sample inhomogeneity combined with classical parabolic magnetoresistance.By analyzing T dependence of Hall mobility,it is found that the main scattering mechanism for electron is electron-electron scattering in the intermediate T region(10K<T<150K),and both electron-electron and longitudinal optical(LO)phonon scatterings limit mobility in the high T region(150 K<T<300 K).Finally,the electrical transport properties of polycrystalline SnO₂ thin films,which were prepared at glass substrates by chemical vapor deposition,have been studied.The effective mass of electrons is 0.31m0,which is obtained by the dependence of optical bandgap on electron concentration.The Hall mobility ? is proportional to T3/2,which indicates the ionized impurity scattering is the dominant elastic scattering mechanism for electrons.The clear negative magnetoresistance is observed at low temperature,which can be attributed to the three-dimensional WL effect.By applying the three-dimensional WL theory,we extracted the electron dephasing length(L?),which decreased on increasing temperature.The temperature dependence of the extracted dephasing length L? ? T-0.75 is found to be dominated by the electron-electron scattering in the small-energy-transfer process.