Isoelectronic recombination center
A certain amount of impurity atoms equivalent to the main atoms are doped into the semiconductor to replace the atoms at the lattice points. Due to the difference in electrical properties between impurity atoms and main atoms, neutral impurity atoms can bind electrons or holes and become charged centers. The charged center attracts carriers with opposite signs to the bound carriers, forming an exciton bound state. This bound state of excitons is called the isoelectronic recombination center.