Photorefractive hole transport materials

Figure 6. The photorefractive effect. Top in an idealized hole transport material, the net charge density is ti radians out of phase with the intensity pattern. Middle the electric field, E, due to this net charge density, p, is given by Gauss law, dEjdx = p/e, and is shifted in phase by njl radians relative to the charge density distribution. Bottom the refractive index will then follow the phase of the electric field. In real materials the charge distribution is not always n radians out of phase relative to the intensity pattern, as competition between drift and diffusion currents leads to a reduced phase shift. The refractive index contrast might therefore be shifted by only n/lO radians relative to the intensity pattern in some polymers.

Specific Examples of Hole Transport Materials for Organic Photorefractives... 

An expression for the internal space-charge field can be obtained through the Kukhtarev model [38] that was developed to describe photorefractivity in most inorganic materials. In this model, the photorefractive material is described by a band model. As for a traditional semiconductor, the material consists of a conduction and a valence bands separated by a band gap as shown in Fig. 13. The model describes the transport of single carrier species and the band gap of the material contains localized energy levels that can be excited optically promoting either holes in the valence band (VB) or electrons in the conduction band (CB). In the model that we adopt here, we assume that the dopant is a donor with an energy level located in the band gap with concentration N. Furthermore, the crystal contains Nj acceptors with that are all ionized and that have accepted a... 

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