66
3 Modification of the Work Function
Fig. 3.32 Schematic plot of change in work function upon film deposition grown in layer-by-layer
mode
A system comprising an overlayer film on an underlayer is often not under thermodynamic equilibrium and undergoes changes in its chemical composition upon heat
treatment via diffusion and segregation, for example, as schematically illustrated in
Fig. 3.33. As a result, the desired work function is often not obtained by deposition
or the work function changes with time. Figure 3.34 shows an example of a change in
the C–V curve (characteristic of band alignment at the interface, which is governed
by the work function) [40]; this will be discussed in detail in Chap. 5. When the work
function is to be modified by deposition, a system should be designed by taking the
diffusion/reaction into account.
Metal-A
Metal-B
(a)
(b)
(c)
Fig. 3.33 Schematic of cross-sectional atomic arrangement for interface modification: a ideal
interface insertion, b mixing at the interface, c reaction at the interface to form a new compound