Session 6 Nonequilibrium Excess Carriers in Semiconductor

Excess electrons in the conduction band and excess holes in the valence band may exist in addition to the thermal-equilibrium concentrations if an external excitation is applied to the semiconductor. Excess electrons and excess holes do not move independently of each other. They diffuse，drift，and recombine with the same effective diffusion coefficient，drift mobility，and lifetime. This phenomenon is called ambipolar transport . The behavior of excess carriersis fundamental to the operation of semiconductor devices.