ABSTRACT
Semiconductors are doped with impurities, the lattices of the semiconductors are distorted and the energy level structures of the semiconductors are also affected. Impurities that supply electrons to be freed easily are called donors. Impurities that supply free holes easily are called acceptors. Luminescence takes place through these impurity levels with wavelengths longer than the bandgap wavelength. When the dopant impurity is changed, the luminescent wavelength and efficiency also change. Excitons moving in a crystal are generally captured by these impurities and bound exciton states are created. When an electron is trapped in an isoelectonic trap, a hole is attracted to the top trap by the Coulomb force, and an exciton bound to an isoelectronic trap is created. The chapter discusses luminescence and related phenomena caused by deep levels in semiconductors. Certain defects and impurities create deep localized levels with large ionization energies.
