carrier introduction
Carriers are particles with electric charges that can move and transport current, including electrons, ions, etc. There are two kinds of carriers in semiconductors, namely, negatively charged free electrons and positively charged free holes. In fact, holes are also valence bond vacancies in semiconductors. The movement of a vacancy is equivalent to the movement of a large group of valence electrons; it is only convenient to use the concept of a small number of holes to describe the movement of a large number of valence electrons. Much more. So, essentially, holes are just another expression for a large group of valence electrons.