Page 955 - Basic Electrical Engineering

type material will create negative ions on the p-side because the atom will
gain one more electron. This way, the number of electrons with negative
charge will be one more than the number of protons with positive charge on

the nucleus. Thus a p-type semiconductor will have negative acceptor ions
and holes as majority carrier.

An n-type semiconductor can be represented by donor impurities because
they give one free electrons to the semiconductor crystal and become positive

ions. p-type and n-type semiconductor materials have been shown side by
side in Fig. 14.5 (a). In the p-type material small circles represent the holes as

the majority carriers. In the n-type material the black dots represent the free
electrons as the majority charge carriers. Electrons are negative charge
carriers while holes are positive charge carriers.

It may be noted that when an electron moves out of an atom, the atom
becomes a positively charged ion which is immobile, i.e., unable to move.

Similarly, addition of an electron in a hole makes an atom a negatively
charged immobile ion. The minority carriers produced due to thermal effect

have not been shown in Fig. 14.5. When a p-type semiconductor is joined
with an n-type semiconductor, as shown in Fig. 14.5 (b), through a special

technique, a junction called p–n junction is formed. We will examine what
happens to the electrons and holes at a p–n junction.