We examine the effects of nonradiative losses on lasing in crystalline and amorphous organic thin films. In crystalline films, the dominant loss mechanism is singlet-singlet annihilation, and this must be avoided if lasing is to be achieved at practical current densities. The electrically pumped crystalline-tetracene laser structure of Schön et al. [Science 289, 599 (2000)] is studied in detail. Optical and electrical confinement in the bulk structure appears unable to explain the spectral narrowing reported; consequently, we consider electron-hole plasmas, self-focusing at interfaces, and crystal defects as possible sources of the reported phenomena. In amorphous films, lasers are likely to have to operate at current densities J < 1000 A/cm2 due to a combination of nonradiative losses. The performance of potential lasing materials is quantified by the external quantum efficiency-current-density product, ηEXTJ. Electrically pumped lasers require ηEXTJ∼5 A/cm2; the best amorphous devices currently posses ηEXTJ∼0.3 A/cm2. However, we demonstrate that electrically pumped lasing in amorphous materials should be possible using indirect pumping techniques.
|Original language||English (US)|
|Number of pages||3178906|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Jul 15 2002|
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