Photoinduced Switching of Charge Carrier Mobility in Conjugated Polymers

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Published on 26 June 2009

In this paper we investigate theoretically a mode of heating thick layers using a laser beam where the temperature of the layer propagates in a steady-state self sustained fashion from the bottom of the layer towards the surface and may exhibit a very steep front. The propagation of the thermal front happens at a constant speed, related to the intensity of the power flux. To achieve this heating mode the absorption coefficient of the layer has to remain low in weak temperatures and increase rapidly as a function of temperature in higher temperatures. Additionally, a significant temperature increase must be generated to trigger this propagation mode, for example through the presence of a strongly absorbing layer beneath the transparent layer. The mode is well suited to semiconductors, especially silicon . The theoretical approach is confirmed by a simulation in the case of a low doped silicon layer 150 micrometers thick above a highly doped substrate ; the low doped silicon is heated homogeneously at 1476 K by a 2E6Wcm^-2 CO₂ laser beam throughought the entire thickness in a timescale of 20µS.