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In the solid-state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers (electrons and electron holes) are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as photodiodes, LEDs and laser diodes. They are also critical to a full analysis of p-n junction devices such as bipolar junction transistors and p-n junction diodes. The electron–hole pair is the fundamental unit of generation and recombination, corresponding to an electron transitioning between the valence band and the conduction band. ==Band structure== Like other solids, semiconductor materials have an electronic band structure determined by the crystal properties of the material. The actual energy distribution among the electrons is described by the Fermi level and the temperature of the electrons. At absolute zero temperature, all of the electrons have energy below the Fermi level; but at non-zero temperatures the energy levels are filled following a Boltzmann distribution. In semiconductors the Fermi level lies in the middle of a ''forbidden band'' or band gap between two ''allowed bands'' called the ''valence band'' and the ''conduction band''. The valence band, immediately below the forbidden band, is normally very nearly completely occupied. The conduction band, above the Fermi level, is normally nearly completely empty. Because the valence band is so nearly full, its electrons are not mobile, and cannot flow as electric current. However, if an electron in the valence band acquires enough energy to reach the conduction band, it can flow freely among the nearly empty conduction band energy states. Furthermore, it will also leave behind an electron hole that can flow as current exactly like a physical charged particle. Carrier ''generation'' describes processes by which electrons gain energy and move from the valence band to the conduction band, producing two mobile carriers; while ''recombination'' describes processes by which a conduction band electron loses energy and re-occupies the energy state of an electron hole in the valence band. In a material at thermal equilibrium generation and recombination are balanced, so that the net charge carrier density remains constant. The equilibrium carrier density that results from the balance of these interactions is predicted by thermodynamics. The resulting probability of occupation of energy states in each energy band is given by Fermi–Dirac statistics. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carrier generation and recombination」の詳細全文を読む スポンサード リンク
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