Chapter 7
Utilization of Interface Potential
The discussion in Chap. 6 revealed that the interface potential gap and the S
parameter determine how the band is aligned at the interface by modifying the work
function of a metal. When the terminating species of a semiconductor (or insulator)
changes at the interface depending on the metals in contact, the concept of the S
parameter no longer applies.
This means that the difference in the metal in contact cannot be handled simply
by considering the work function φ m within the frame of the jellium model. In
this chapter, some examples of band alignment modification beyond jellium-based
models, i.e., the intentional, direct tuning of the interface potential gap , are
demonstrated.
7.1 Control of Interface-Terminating Species
The generalized charge neutrality level (generalized CNL) in Sect. 6.5 was proposed
on the basis of the experimental finding that the S parameter exceeds 1 (S > 1) when
the interface-terminating species depends on the metals in contact. However, this
model does not explicitly include interface-terminating species in its definition of
the generalized CNL. It has been experimentally shown that interface-terminating
species can be modified by controlling the formation of Cu–Al 2 O 3 interfaces [1, 2].
The interface-terminating species is known to strongly affect the strength of Cu–
Al 2 O 3 interface bonding [3–5]. Interface termination with other metals has been
studied from the thermodynamic viewpoint [6]. In short, for the same metal–oxide
material combination, interface-terminating species can be different, as shown in
Fig. 7.1, and stable termination is determined by the thermodynamics of each system.
Regarding the Schottky barrier height (SBH) for a differently terminated interface,
first-principles calculations have predicted that the p-type Schottky barrier height (pSBH) (or band offset, i.e., the energy difference between the Fermi level and the
© National Institute for Materials Science, Japan 2021
M. Yoshitake, Work Function and Band Alignment of Electrode Materials,
NIMS Monographs, https://doi.org/10.1007/978-4-431-56898-8_7
127
Utilization of Interface Potential
The discussion in Chap. 6 revealed that the interface potential gap and the S
parameter determine how the band is aligned at the interface by modifying the work
function of a metal. When the terminating species of a semiconductor (or insulator)
changes at the interface depending on the metals in contact, the concept of the S
parameter no longer applies.
This means that the difference in the metal in contact cannot be handled simply
by considering the work function φ m within the frame of the jellium model. In
this chapter, some examples of band alignment modification beyond jellium-based
models, i.e., the intentional, direct tuning of the interface potential gap , are
demonstrated.
7.1 Control of Interface-Terminating Species
The generalized charge neutrality level (generalized CNL) in Sect. 6.5 was proposed
on the basis of the experimental finding that the S parameter exceeds 1 (S > 1) when
the interface-terminating species depends on the metals in contact. However, this
model does not explicitly include interface-terminating species in its definition of
the generalized CNL. It has been experimentally shown that interface-terminating
species can be modified by controlling the formation of Cu–Al 2 O 3 interfaces [1, 2].
The interface-terminating species is known to strongly affect the strength of Cu–
Al 2 O 3 interface bonding [3–5]. Interface termination with other metals has been
studied from the thermodynamic viewpoint [6]. In short, for the same metal–oxide
material combination, interface-terminating species can be different, as shown in
Fig. 7.1, and stable termination is determined by the thermodynamics of each system.
Regarding the Schottky barrier height (SBH) for a differently terminated interface,
first-principles calculations have predicted that the p-type Schottky barrier height (pSBH) (or band offset, i.e., the energy difference between the Fermi level and the
© National Institute for Materials Science, Japan 2021
M. Yoshitake, Work Function and Band Alignment of Electrode Materials,
NIMS Monographs, https://doi.org/10.1007/978-4-431-56898-8_7
127