Excitons in Biological and Non-Biological Nano-Structured Systems: Progress Towards Bio-inspired Photodetectors

An exciton, an elementary excitation formed from a bound electron-hole pair, is the lowest optically excited state in semiconductors, and plays a prominent role in condensed matter physics. In reduced dimensional materials, including biological structures, excitonic transitions should dominate due to carrier confinement. Here, I will first describe excitonic transitions in the photocurrent spectra of carbon nanotube diodes as a model system to describe optical absorption in ID semiconductors. The sharp narrow peaks are associated with excitonic transitions, and peak # 1 corresponds to the lowest optically allowed exciton state. The observation of sharp narrow absorption peaks at room temperature in a semiconductor is unprecedented, and is due to strong optical transitions of excitons as compared to band-to-band transitions normally seen for bulk materials.