Both n -type and p -type materials are formed by adding a predetermined number of impurity
atoms to a silicon base. An n -type material is created by introducing impurity elements that
have five valence electrons ( pentavalent ), such as antimony , arsenic , and phosphorus. Each is
a member of a subset group of elements in the Periodic Table of Elements referred to as Group
V because each has five valence electrons. The effect of such impurity elements is indicated in
Fig. 1.7 (using antimony as the impurity in a silicon base). Note that the four covalent bonds
are still present. There is, however, an additional fifth electron due to the impurity atom, which
is unassociated with any particular covalent bond. This remaining electron, loosely bound to
its parent (antimony) atom, is relatively free to move within the newly formed n -type material.
Since the inserted impurity atom has donated a relatively “free” electron to the structure: