Carrier Generation

  • Karl W. Böer
  • Udo W. PohlEmail author
Living reference work entry

Later version available View entry history



When the semiconductor is exposed to an external electromagnetic field, a phonon field, or an electric field, free carriers can be generated, resulting in semiconductivity or photoconductivity. Carriers can also be generated by high-energy particles, such as fast electrons or ions. Optical carrier generation proceeds as band-to-band direct or indirect generation or from defect levels with photons of sufficient energy. Thermal generation of free carriers is substantially enhanced by defect centers. Shallow centers may absorb a phonon of sufficient energy or a few phonons involving intermediate steps into excited states; generation from deep centers requires multiphonon-induced giant oscillations.

Generation of carriers by an electric field can at low fields be caused by the Frenkel-Poole effect: a field-enhanced thermal generation from Coulomb-attractive defect centers. At high fields, impact ionization from deep centers or band-to-band impact ionization is observed. At still higher fields in the 106 V/cm range, tunneling from deep defect centers or from the valence band occurs. Besides thickness and height of the barrier, the tunneling probability depends on the shape of the barrier potential.


Avalanche multiplication Band-to-band tunneling Defect-assisted carrier generation Dielectric breakdown Field ionization Franz-Keldysh effect Frenkel-Poole effect Impact ionization Multiplication factor Optical carrier generation Thermal ionization Transition probability Transition rate Tunneling Tunneling current Tunneling spectroscopy 


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© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.NaplesUSA
  2. 2.Institut für Festkörperphysik, EW5-1Technische Universität BerlinBerlinGermany

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