Video Transcript
Which of the following are considered mobile carriers of charge in a semiconductor diode? (A) Free electrons only, (B) vacancies only, (C) both free electrons and vacancies, (D) neither free electrons nor vacancies.
A semiconductor diode is a device made of two materials. One is called a p-type material, and the other is called an n-type. Here, p and n stand for positive and negative, respectively. And they refer to the mobile charge carriers for each of these types. In the p-type half of a semiconductor diode, the mobile carriers of charge are called holes or vacancies. They have this name because electrons could fill these vacancies. But so long as they don’t, the overall charge of these holes or vacancies is considered to be positive.
Just like free electrons, holes can move about through the material. In a p-type material then, the mobile carriers of charge are vacancies. In an n-type material though, the mobile charges are electrons. These are electrons that have been freed from any particular atom so that they, like vacancies, can move all around through the material. Since a semiconductor diode is always made of one p-type and one n type material joined together, we know that they will have both free electrons and vacancies as their mobile charge carriers. We choose answer option (C).
