1. State the differences in operation and application for junction transistors and MOSFETs.

2. We note in Section 12.5 (Figure 12.20) that in FeO (wüstite), the iron ions can exist in both Fe²⁺ and Fe³⁺ states. The number of each of these ion types depends on temperature and the ambient oxygen pressure. Furthermore, we also note

that in order to retain electroneutrality, one Fe²⁺ vacancy will be created for every two Fe³⁺ ions that are formed; consequently, in order to reflect the existence of these vacancies the formula forwüstite is often represented as Fe(1−x)O, where x is some small fraction less than unity. In this nonstoichiometric Fe(1−x)O material, conduction is electronic, and, in fact, it behaves as a p-type semiconductor—that is, the Fe³⁺ ions act as electron acceptors, and it is relatively easy to excite an electron from the valence band into an Fe³⁺ acceptor state, with the formation of a hole. Determine the electrical conductivity of a specimen of wüstite that has a hole mobility of 1.0 × 10⁻⁵ m²/V·s and for which the value of x is 0.060.

Assume that the acceptor states are saturated (i.e., one hole exists for every Fe³⁺ ion). Wüstite has the sodium chloride crystal structure with a unit cell edge length of 0.437 nm.