| abstract |
When the density of excitons in an organic single crystal (including the linear acenes, polyacenes, and thiophenes) approaches the density of molecular sites, an electron-hole plasma may form in the material altering the overall excitonic character of the system. The formation of the electron-hole plasma arises as a result of the screening of Coulomb interactions within individual excitons by injected free carriers. The large exciton densities required to accomplish this screening process can only be realized when excitons collect near dislocations, defects, traps, or are confined in heterostructures. Such confinement and subsequently large exciton densities allows for the observation of physical phenomena not generally accessible in an organic material. Specifically, the formation of an electron-hole plasma in an organic single crystal can allow for the observation of field-effect transistor action and electrically-pumped lasing. Amorphous organic materials and polymeric organic materials can also used to sustain an electron-hole plasma and demonstrate similar phenomena as well. |