- Photo-dember
In
semiconductor physics the photo-Dember effect (named after its discoverer H. Dember [1] ) consists in the formation of a chargedipole in the vicinity of asemiconductor surface after ultra-fast photo-generation ofcharge carriers [2-4] . Thedipole forms owing to the difference of mobilities (ordiffusion constants) for holes andelectrons which combined with the break of symmetry provided by the surface lead to an effective charge separation in the direction perpendicular to the surface.One of the main applications of photo-Dember effect is the generation of
terahertz (THz)radiation pulses forterahertz time domain spectroscopy . This effect is present in most semiconductors but it is particularly strong in narrow band-gap semiconductors (mainly arsenides and antimonides) such as InAs [2,3] and InSb [4] owing to their highelectron mobility . The photo-Dember terahertz emission should not be confused with the surface field emission which occurs if the surfaceenergy bands of asemiconductor fall between itsvalence andconduction bands, which produces a phenomenon known asFermi level pinning, causing, at its time, band bending and consequently the formation of adepletion oraccumulation layer close to the surface which contributes to theacceleration ofcharge carriers [2] . These two effects can contribute constructively or destructively for thedipole formation depending on the direction of the band-bending.(1) H. Dember, Phys. Z. 32, 554 (1931)
(2) http://dx.doi.org/10.1103/PhysRevB.65.165301
(3) http://dx.doi.org/10.1103/PhysRevB.53.4005
(4) http://dx.doi.org/10.1007/s003400000455
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