Interlayer Exciton Optoelectronics in a 2D Heterostructure p-n Junction (1701.00802v1)

Abstract: Semiconductor heterostructures are backbones for solid state based optoelectronic devices. Recent advances in assembly techniques for van der Waals heterostructures has enabled the band engineering of semiconductor heterojunctions for atomically thin optoelectronic devices. In two-dimensional heterostructures with type II band alignment, interlayer excitons, where Coulomb-bound electrons and holes are confined to opposite layers, have shown promising properties for novel excitonic devices, including a large binding energy, micron-scale in-plane drift-diffusion, and long population and valley polarization lifetime. Here, we demonstrate interlayer exciton optoelectronics based on electrostatically defined lateral p-n junctions in a MoSe2-WSe2 heterobilayer. Applying a forward bias enables the first observation of electroluminescence from interlayer excitons. At zero bias, the p-n junction functions as a highly sensitive photodetector, where the wavelength-dependent photocurrent measurement allows the direct observation of resonant optical excitation of the interlayer exciton. The resulting photocurrent amplitude from the interlayer exciton is about 200 times smaller compared to the resonant excitation of intralayer exciton. This implies that the interlayer exciton oscillator strength is two orders of magnitude smaller than that of the intralayer exciton due to the spatial separation of electron and hole to opposite layers. These results lay the foundation for exploiting the interlayer exciton in future 2D heterostructure optoelectronic devices.

• The paper reveals that interlayer excitons exhibit strong binding energy and prolonged valley polarization, validating their potential in excitonic devices.
• The study employs electrostatically defined p-n junctions to achieve electroluminescence and high photodetection sensitivity in the MoSe2-WSe2 heterobilayer.
• The findings advance nanoscale device engineering by distinguishing emission features of interlayer versus intralayer excitons for improved optoelectronic design.

Interlayer Exciton Optoelectronics in 2D Heterostructure p-n Junctions: Implications and Advances

The paper "Interlayer Exciton Optoelectronics in a 2D Heterostructure p-n Junction" by Ross et al. presents a detailed exploration of interlayer exciton dynamics within a two-dimensional (2D) heterostructure, specifically within a molybdenum diselenide (MoSe$_2$)-tungsten diselenide (WSe$_2$) heterobilayer. The paper leverages advances in van der Waals heterostructure assembly techniques to explore the properties and potential applications of interlayer excitons, which are tightly bound electron-hole pairs situated in separate layers. This work encompasses both theoretical insights and experimental results, contributing to the expanding body of knowledge concerning the use of 2D materials in optoelectronics.

Key Contributions

1. Interlayer Exciton Characteristics: The paper demonstrates that interlayer excitons exhibit significant binding energy, long populations, and valley polarization lifetimes. These properties enable their potential use in novel excitonic devices due to their lower oscillator strengths, a quality attributed primarily to the spatial electron-hole separation.
2. Electroluminescence and Photodetection: By utilizing electrostatically defined lateral p-n junctions within the heterobilayer, the paper records electroluminescence from interlayer excitons when a forward bias is applied. At zero bias, the structure serves as an ultra-sensitive photodetector, revealing an ability to directly observe resonant optical excitation of interlayer excitons.
3. Device Innovation and Performance: The experimental setup includes using palladium back gates to create separate p and n regions, facilitating layer-specific carrier injection. The interlayer exciton was found to contribute an emission peak energy distinguishing it distinctly from intralayer exciton emissions, providing critical insights for device design and application.
4. Nanoscale Phenomena and Measurement: The interlayer exciton photodetector shows amplitude that is approximately two orders of magnitude smaller than intralayer excitons, correlating to previous theoretical predictions and highlighting the importance of excitonic dynamics concerning interlayer separation.

Implications and Future Directions

The findings encapsulated in this paper suggest a profound potential for interlayer excitons in next-generation optoelectronic applications. The documented sensitivity in photodetectors utilizing interlayer excitons offers pathways for development in low-light and wavelength-specific detection technologies. Furthermore, the observation of electroluminescence opens avenues for developing light-emitting devices powered by interlayer excitons.

Practical implications for 2D heterostructures extend to improved understanding and manipulation of electronic properties inherent in materials such as transition metal dichalcogenides (TMDs), with direct potential in phototransistors, photovoltaic systems, and beyond. Ongoing research addressing the role of layer twist angle and crystal alignment in excitonic properties will explore tuning exciton dynamics for device optimization.

The paper underscores an emergent trend whereby atomic-scale engineering and characterization techniques are revolutionizing the fabrication and application of semiconductor devices. Future advancements are likely to involve integration of these 2D materials in complex systems, increasing their interface with electronic, optical, and quantum computing domains.

Overall, this work exemplifies a significant step towards harnessing the unique physical properties of interlayer excitons, facilitating innovative application in optoelectronics and extending theoretical models to encompass a diverse range of phenomena intrinsic to 2D material systems.