December effect

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The Dember Effect , also known as the Photo Dember Effect or Crystal Photo Effect , is named after the physicist Harry Dember (1882–1943). It describes the creation of an electrical voltage when light shines on a semiconductor .

description

December effect

Physically, the Dember effect is based on the following cause: When light shines with sufficient energy (or sufficiently short wavelength) onto the semiconductor, electrons are lifted from the valence band over the band gap of the semiconductor ( photoelectric effect ). So-called electron-hole pairs are created (holes are missing electrons in the valence band of the semiconductor). Since the light is absorbed in the semiconductor, the density of the electron-hole pairs is highest on the surface and decreases in the semiconductor. This spatial decrease in the electron-hole pairs follows an exponential decrease, the Lambert-Beer law . The gradient of the electron-hole pairs leads to oneDiffusion current in the semiconductor. Now electrons and holes have different weights, they have different effective masses . As a rule, the effective masses of the electrons are smaller than those of the holes, which is why electrons diffuse faster into the semiconductor. This sets in a spatial separation of electrons and holes. This spatial separation of electrons (negative charges) and holes (positive charges) creates an electrical voltage.

application

The December effect is also relevant for the generation of terahertz radiation from semiconductors. If a short pulse of light hits a semiconductor, the electrical voltage builds up due to the December effect. If the light pulse is generated by a femtosecond laser , the voltage builds up within less than a picosecond. This process emits electromagnetic radiation in the terahertz frequency range, which was first observed by Thomas Dekorsy .

See also

literature

  • Harry Dember: About a photoelectronic force in copper oxide crystals . In: Physikalische Zeitschrift . tape 32 , 1931, pp. 554 .
  • Harry Dember: On the advancement of electrons through light . In: Physikalische Zeitschrift . tape 33 , 1931, pp. 207 .
  • Peter Würfel: Physics of Solar Cells . 2nd Edition. Spektrum Akademischer Verlag, 2000, ISBN 3-8274-0598-X , p. 116 ff .
  • Maja Krčmar, Wayne M. Saslow: Exact surface solutions for semiconductors: The December effect and partial currents . In: Physical Review B . tape 65 , no. 23 , 2002, p. 233313 , doi : 10.1103 / PhysRevB.65.233313 .

Individual evidence

  1. ↑ Thomas Dekorsy, T. Pfeifer, W. Kütt, H. Kurz: Subpicosecond carrier transport in GaAs surface-space-charge fields . In: Physical Review B . tape 47 , no. 7 , 1993, pp. 3842-3849 , doi : 10.1103 / PhysRevB.47.3842 .
  2. ↑ Thomas Dekorsy, H. Auer, HJ Bakker, HG Roskos, H. Kurz: THz electromagnetic emission by coherent infrared-active phonons . In: Physical Review B . tape 53 , no. 7 , 1996, pp. 4005-4014 , doi : 10.1103 / PhysRevB.53.4005 .