Capacitance-voltage analysis of high-carrier-density SrTiO_3/GdTiO_3 heterostructures

摘要

We report on capacitance-voltage (C-V) analysis of SrTiO_3/GdTi_O3 heterostructures that contain a high-density, two-dimensional electron gas (2DEG) at the interface. The complex admittance was measured as a function of frequency for different gate biases applied to a Schottky contact on the SrTiO_3. A one-dimensional, complex impedance transmission line model was used to extract C-V characteristics from the frequency dependent admittance. The extracted capacitance was nearly independent of the gate voltage (up to -0.5 V), indicating a fully depleted SrTiO_3 layer. The results are used to estimate the dielectric constant of the SrTiO_3, the degree of modulation of the 2DEG by the maximum applied voltage (～2.5%), and to establish an upper limit of the residual carrier density in the bulk of the SrTiO_3 film (～9 × 10~(18) cm~(-3)).