Termination control of the interface dipole in ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3/\text{Nb}:{\text{SrTiO}}_3$ (001) Schottky junctions

In order to investigate the interface termination dependence of perovskite band alignments, we have studied the Schottky barrier height at ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3/\text{Nb}:{\text{SrTiO}}_3$ (001) heterointerfaces. As the $\text{Nb}:{\text{SrTiO}}_3$ semiconductor was varied from ${\text{TiO}}_2$ termination to SrO termination by variable insertion of a ${\text{SrMnO}}_3$ layer, a large systematic increase in the Schottky barrier height was observed. This can be ascribed to the evolution of the interface dipole induced to screen the polar discontinuity at the interface, which gives a large internal degree of freedom for tuning band diagrams in oxides.

Figure 1

(Color online) The two different possible interfaces between the perovskites ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3$ and ${\text{SrTiO}}_3$ joined in the [001] direction: (a) ${\text{TiO}}_2$-terminated and (b) SrO-terminated ${\text{SrTiO}}_3$.

Figure 2

(Color online) RHEED intensity monitored during the deposition of varying thicknesses of ${\text{SrMnO}}_3$. The arrow denotes the start of deposition.

Figure 3

(Color online) (a) Current-voltage and (c) capacitance-voltage characteristics of ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3/{\left({\text{SrMnO}}_3\right)}_x/\text{Nb}:{\text{SrTiO}}_3$ junctions at room temperature for different interface compositions. [(b) and (d)] Histograms of the obtained SBH and $V_{\text{bi}}$ from (a) and (c) in steps of 0.04 V normalized by the total number of measurements. The curves show best Gaussian fits.

Figure 4

(Color online) (a) Schematic of IPE. The electrons surmounting the barrier height are detected as photocurrent. (b) IPE spectra of ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3/{\left({\text{SrMnO}}_3\right)}_x/\text{Nb}:{\text{SrTiO}}_3$ junctions at room temperature. The square root of the photoyield is plotted against the photon energy.

Figure 5

(Color online) Summary of the obtained barrier heights from $I\text{−}V$ (○, red), $C\text{−}V$ (◻, blue), and IPE (△, black) measurements. The dotted line (green) indicates the variation in the screening dipole in a simple ionic model (see text for details).

Figure 6

(Color online) (a) A schematic diagram of the ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3/\text{Nb}:{\text{SrTiO}}_3$ interface charge sheet density and the electrostatic potential for 0.0 (left) and 1.0 uc (right) of ${\text{SrMnO}}_3$ coverage. The small arrows in ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_3$ represent the compensation charges induced to screen the interface. The relative electrostatic potential across the interface varies depending on the interface termination, consequently changing the band alignment (b) at the interface (see text for details).