Impedance-based interpretations in 2-dimensional electron gas conduction formed in the LaAlO₃/Sr_xCa_1-xTiO₃/SrTiO₃ system

Frequency-dependent impedance spectroscopy was applied to the 2-dimensioanl conduction transport in the LaAlO₃/Sr_xCa_1-xTiO₃/SrTiO₃ system. The 2-dimensional conduction modifies the electrical/dielectric responses of the LaAlO₃/Sr_xCa_1-xTiO₃/SrTiO₃ depending on the magnitude of the interfacial 2-dimensional resistance. The high conduction of the 2-dimensional electron gas (2DEG) layer can be described using a metallic resistor in series with two parallel RC circuits. However, the high resistance of the 2-dimensional layer drives the composite system from a finite low resistor in parallel with the surrounding dielectrics composed of LaAlO₃ and SrTiO₃ materials to a dielectric capacitor. This change in the resistance of the 2-dimensional layers modifies the overall impedance enabled by the presence of the interfacial layer due to Sr_xCa_1-xTiO₃, which alters the charge transport of the 2-dimensional layer from metallic to semiconducting conduction. A noticeable change is observed in the capacitance Bode plots, indicating highly amplified dielectric constants compared with the pristine SrTiO₃ substrates and Sr_xCa_1-xTiO₃ with a greater Ca content.