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

TLDR

The low charge‑carrier mobility in organic semiconductors limits film thickness to <100 nm and causes carrier‑induced changes in optical properties under intense electrical excitation. The study proposes organic waveguide laser structures comprising thin organic films and transparent indium‑tin‑oxide electrodes, emphasizing the need to account for these effects in device design and material selection. These waveguides enable efficient current injection and low optical loss, while the authors examine electrically induced optical changes using electroluminescence and pump‑probe spectroscopy. They report induced transparency and absorption associated with triplet excitons or trapped carriers, and observe pump‑induced absorption in organic films under quasi‑continuous‑wave optical excitation.

Abstract

The challenges to realizing diode lasers based on thin films of organic semiconductors are primarily related to low charge carrier mobility in these materials. This not only limits the thickness of organic films to /spl les/100 nm in electrically pumped devices, but it also leads to changes in the optical properties of organic films induced by the large number of carriers trapped in the materials subjected to an intense electrical excitation. We describe organic waveguide laser structures composed of thin organic films and transparent indium-tin-oxide electrodes. These waveguides allow for efficient injection of an electrical current into the organic layers and provide for low optical losses required in a laser. The changes in the optical properties of organic thin films induced by electrical excitation are studied using electroluminescence and pump and probe spectroscopy. Induced transparency and absorption observed in the organic materials may be related to triplet excitons or trapped charge carriers. Pump-induced absorption is also observed in organic films under quasi-CW optical excitation. These effects must be taken into account both in the design of organic diode laser structures and in the selection of charge transporting materials.