Recombination of an Electron and a Hole in a Semiconductor

the disappearance of a conduction electron and a hole as charge carriers as a result of the transition of the electron from the conduction band to the valence band. In radiative recombination, the excess energy is released in the form of radiation. Nonradiative recombination can also occur. In this case, the released energy excites lattice vibrations or—in impact recombination, which requires the collision of three carriers—is transferred to a free charge carrier. In addition to the direct recombination of an electron with a hole, there also occurs indirect recombination through recombination centers, wherein the electron first is captured from the conduction band by an impurity level in the energy gap and then passes to the valence band. The recombination rate, which is the number of recombination events per unit time, determines (1) the concentration of nonequilibrium charge carriers created by an external factor, such as light or fast charged particles, and (2) the recovery time of equilibrium concentration after the factor is removed. Radiative recombination is evidenced in the luminescence of crystals and is the basis for the action of lasers and light-emitting diodes.