Dielectric Engineering Boosts the Efficiency of Carbon Nanotube Photodiodes.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 34105938.
- Also identified by DOI 10.1021/acsnano.1c02940.
- No licence information is recorded for this record.
- Because redistribution is not established, this page shows the abstract only. Follow the links below for the full text.
Abstract
Carbon nanotube (CNT) photodiodes are a promising system for high-efficiency photocurrent generation due to the strong Coulomb interactions that can drive carrier multiplication. If the Coulomb interactions are too strong, however, exciton formation can hamper photocurrent generation. Here, we explore, experimentally and theoretically, the effect of the environmental dielectric constant (ε<sub>env</sub>) on the photocurrent generation process in CNTs. We study individual ultraclean CNTs of known chiral index in a vacuum or dry nitrogen gas (ε<sub>env</sub> = 1) and oil (ε<sub>env</sub> = 2.15). The efficiency of photocurrent generation improves by more than an order of magnitude in oil. Two mechanisms explain this improvement. First, the refractive index of the environment optimizes the interference between incident and reflected light. Second, exciton binding energies are reduced in oil, changing the relaxation pathways of photoexcited carriers. We varied the axial electric field in the pn junction from 4 to 14 V/μm. Our measurements at high field indicate that autoionization of second-subband excitons can coexist with carrier multiplication. Dielectric screening makes this coexistence regime more accessible and allows us to reach photocurrent quantum yields greater than 100%.