Structures for organic diode lasers and optical properties of organic semiconductors under intense optical and electrical excitations

The challenges to realizing diode lasers based an thin films of organic sem iconductors are primarily related to low charge carrier mobility in these m aterials, This not only limits the thickness of organic films to less than or equal to 100 nm in electrically pumped devices, but it also leads to cha nges in the optical properties of organic films induced by the large number of carriers trapped in the materials subjected to an intense electrical ex citation. We describe organic waveguide laser structures composed of thin o rganic films and transparent indium-tin-oxide electrodes, These waveguides allow for efficient injection of an electrical current into the organic lay ers and provide for low optical losses required in a laser, The changes in the optical properties of organic thin films induced by electrical excitati on are studied using electroluminescence and pump and probe spectroscopy. I nduced transparency and absorption observed in the organic materials may be related to triplet excitons or trapped charge carriers. Pump-induced absor ption is also observed in organic films under quasi-CW optical excitation. These effects must be taken into account both in the design of organic diod e laser structures and in the selection of charge transporting materials.