Group III-V Semiconductors

In the previous sections, we have been discussing the donor and acceptor impurities in a group IV semiconductor, such as silicon. The situation in the group Ill-V

Table 1.1 Impurity ionuatian energles in galhumar senlde.

compound semiconductors, such as gallium arsenide, is more complicated. Group II elements, such as beryllium, zinc, and cadmium, can enter the lattice as substitutional impurities, replacing the group I11 gallium element to become acceptor impurities. Similarly, group VI elements, such as selenium and tellurium, can enter the lattice substitutionally, replacing the group V arsenic element to become donor impurities.

The corresponding ionization energies for these impurities are smaller than for the impurities in silicon. The ionization energies for the donors in gallium arsenide are also smaller than the ionization energies for the acceptors, because of the smaller effective mass of the electron compared to that of the hole.

Group IV elements, such as silicon and germanium, can also be impurity atoms in gallium arsenide. If a silicon atom replaces a gallium atom, the silicon impurity will act as a donor. but if the silicon atom replaces an arsenic atom. then the silicon impurity will act as an acceptor. The same is true for germanium as an impurity atom. Such impurities are called amphoteric. Experimentally in gallium arsenide, it is found that germanium is predominantly an acceptor and silicon is predominantly a donor. Table 1.1 lists the ionization energies for the various impurity atoms in gallium arsenide.