1.1. Schottky Junctions.

The ability to predict the Schottky barrier height (SBH) for all metal-semiconductor junctions has eluded scientists to date. One reason for this state of affairs is that for many junctions the structure and composition of the interface region is not known. To understand why this knowledge is necessary it is helpful to consider Schottky's original model for this junction as follows. Consider the case of a metal which has a work function, ? _M, larger than the electron affinity, ? _S, of an n-type semiconductor, where these quantities are defined as the difference between the vacuum level and the Fermi levels of the electron in the bulk materials, respectively. Let us assume that relative to the vacuum level the conduction electrons in the metal have a lower chemical potential than those in the semiconductor. Thus, when contact is made between the two materials electrons will transfer to the metal building up at the interface until the chemical potential is equal in the two components of the junction. This charge derives from the near-surface region of the semiconductor adjacent to the metal. Figure 6.1 taken from Phillips's book1 shows an electron energy-distance diagram for various steps in the process of making the junction under the assumption that a wire of decreasing length connects the metal and semiconductor. As shown there the consequence of the contact is an energy barrier between metal and semiconductor with height equal to