The Electrical Transport Properties Of Amorphous InGaZnO₄ Films

Amorphous Indium-Gallium-Zinc oxide(a-IGZO),which simultaneously possesses high optical transparency(80%avgT(29))in visible light,high mobility(2-1-1m(28)10 ~ 100 cm V s),low temperature fabrication process and good uniformity,is being considered as a good active channel material of thin-film-transistors(TFTs)in next generation transparent flat-panel/flexible displays such as paper displays,liquid crystal displays.So far,the experimental and theoretical investigations of a-IGZO have mainly focused on the IGZO-TFT performance optimization from the viewpoint of stability and response rate.However,systematical works concerning the electrical transport mechanism in a-IGZO films are very few,and there remain some problems to be solved.In this work,two series of a-IGZO thin films were prepared by radio frequency sputtering method at different substrate temperatures,and the electrical transport mechanisms especially the quantum corrections of the films are in-depth investigated.The first(second)series of films were intentionally fabricated to a thickness of ~700 nm(~25 nm).From scanning electron microscopy images of films,we conclude that the a-IGZO film is consisted of many spherical particles with distinct boundary between amorphous particles.In the thin a-IGZO films,the thickness(~25 nm)is comparable with the particle size(~30 nm).We found that the temperature dependence of the resistivities of all a-IGZO films can be well described by the Bloch-Grüneisen law at high temperature region,and demonstrates that a-IGZO films possess metallic transport property.Whereas at low temperature regime,the resistivities slightly increasing with the decrease of temperature.We sysmetically measured the variations of resistivity and Hall coefficient with temperature for the thick(~700 nm)and thin(~25 nm)a-IGZO films from 300 down to 2 K.Quantitative analysis manifests that the low temperature conduction process of a-IGZO films cannot be described by the electron-electron interaction effect in the homogeneous disordered conductors.The EEI effect in the presence of granularity governs the temperature behaviors of longitudinal and Hall transport of the a-IGZO films,namely the films obey the laws(35)s ?ln T and lnH(35)R ?T.We conclude that the subtle influence of boundary between the amorphous particles in a-IGZO films on the electronic transport processes could not be neglected.To further analyze the electrical dephasing peocesses,we measured the magnetoresistance with temperature range of 2~20 K.According to the weak-localization theory,we obtain the relationship between the electron dephasing rate and temperature.Quantitative analysis manifests that the small-and large-energy-transfer e-e scattering dominate the electron dephasing processes in the thin films,while only small-energy-transfer e-e scattering dominate electron dephasing processes in the thick films at low temperature.This electron dephasing mechanism dominates over the electron-phonon scattering process because the carrier concentrations in our films are 3~4 orders of magnitude lower than those in typical metals,which resulted in a greatly suppressed electron-phonon relaxation rate and a greatly raised electron-electron scattering rate,so as to that the electron-electron scattering dominates the dephasing process.