Berlin 2005 – wissenschaftliches Programm
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SYOO: Organic Optoelectronics and Photonics
SYOO 2: Optoelectronic Properties
SYOO 2.6: Vortrag
Montag, 7. März 2005, 12:45–13:00, TU C130
Modelling of modal gain and laser threshold in electrically pumped organic semiconductor optical amplifier and laser diode structures — •Christof Pflumm, Christian Karnutsch, Martina Gerken, and Uli Lemmer — Lichttechnisches Institut, Universität Karlsruhe, Kaiserstraße 12, 76128 Karlsruhe
We present a model to calculate the modal gain in organic optical amplifiers and the threshold power density in organic laser diode structures. The dependence of the modal gain and threshold power density on electron and hole mobility, injection barriers and the thickness of the active layer is investigated. In order to achieve appreciable gain of ≈ 1/cm at a power density of P=50kW/cm2, equal charge carrier mobilities are of crucial importance. For injection barriers up to φb=0.3 eV, the gain remains nearly constant. If different devices are compared on the basis of equal power density, there is an optimum thickness for the active layer of d ≈ 200 nm. Power laws for the dependence of modal gain on mobility and power density are derived. These can serve as guidelines for future device design considerations. To quantify the influence of polaron absorption in optical amplifiers, a figure of merit ζ is introduced. For the most favourable parameters, the polaron absorption cross section has to be at least twenty times smaller than the cross section for stimulated emission in order to achieve net gain. We investigate the dependence of the laser threshold power density on the above mentioned parameters. For the optimum case considered, the power density necessary for lasing in the considered single layer devices is 25 times higher than the highest value reported in the literature to date.