Once principal components are obtained, these main components are naturally subject to interpretation. Initially, it is not determined at all, that the principal components have a direct physical meaning, they primarily simplify the data set. Only secondary exclusions and comparisons allow for their interpretation. Factor 1 can be considered to be strongly influenced by the sheet charge density , if not the sheet carrier density itself. The following reasoning explains this idea:
For Factor 2, no direct physical correlation could be found.
More generally, the variations in III-V HEMTs processing are different from those typical from silicon CMOS due to the wafer size. For 2-4 inch wafers the statistical sample is smaller and singular events and systematic changes mix. A list of typical variations is given in the following, some origins of these variations are given in the next section.
Stepping from 4 inch to 6 and 8 inch wafers the importance shifts from singular events to statistical variations due to the increase of the cell numbers in the sample.