tesi R. Miscioscia.pdf - EleA@UniSA

Chapter 2 63
materials, the higher is the current passing through the junction itself.
Thus, for p-type transistor, the contact is much better as the WF of the
contact approaches the semiconductor HOMO level (in which we
would like to inject holes).
Many p-type materials have HOMO levels that require, for the
adequate holes injection, high work-function electrodes to minimize
the interface barrier. For example, for p-type pentacene based
transistors, it will be sufficient to use metals such as gold, nickel,
platinum, etc. to realize the appropriate source and drain contacts (see
table 1).
Metal WF(eV)
Au 5.10
Pt 5.65
Ni 5.15
Co 5.00
Cu 4.65
table 1: some metals having high work-function
The issues related to the energy bands alignment between
Source/Drain and semiconductor were extensively investigated in the
literature for many materials combinations.
In figure 33, it is shown a diagram about the situation of the
energy levels that exists between a gold contact and the HOMO level
of a pentacene film, as described by Horowitz in an interesting paper
[7].