New conductive-bridge interlayer contacts could boost performance of 2D optoelectronics

Photodiodes are widely used devices based on semiconducting materials that can convert light into electrical current. These devices are central components of various contemporary technologies, including photovoltaics (PVs) and some sensing, imaging, measurement and communication systems.

In recent years, engineers have been trying to devise new design strategies that could further improve the performance of photodiodes and the efficiency with which they convert light into electricity. One proposed approach entails their fabrication using two-dimensional (2D) semiconductors, which are only a few atomic layers thin and exhibit advantageous properties.

Despite their potential, many 2D semiconductor-based photodiodes fabricated so far have not performed as well as expected. This is in great part due to a phenomenon known as Fermi level pinning, which entails a fixation of the energy level at the interface between a metal and semiconductor.

Researchers at the Korea Institute of Science and Technology (KIST), Korea University, Yonsei University and other institutes in South Korea designed and fabricated new conductive-bridge interlayer contacts that could help to enhance the charge transport of 2D photodiodes. Their paper, published in Nature Electronics, could open new possibilities for the future advancement of optoelectronic devices.

“Photodiodes based on two-dimensional semiconductors are of potential use in the development of optoelectronic devices, but their PV efficiency is limited by strong Fermi level pinning at metal-semiconductor contacts,” Jisu Jang, Jung Pyo Hong, and their colleagues wrote in their paper. “Typical metal-interlayer-semiconductor contacts can address this issue, but can also lead to an increase in series resistance. We report a conductive-bridge interlayer contact that offers both Fermi level depinning and low resistance.”

The conductive-bridge interlayer contact developed by Jang, Hong and their colleagues is essentially a thin insulating layer that separates the metal inside a photodiode from a 2D semiconductor. This thin interlayer is made of an oxide material with gold nanoclusters (i.e., tiny conductive particles) embedded in it.

“We create an oxide interlayer that decouples the metal and semiconductor, while embedded gold nanoclusters in the interlayer act as conductive paths that facilitate efficient charge transport,” wrote Jang, Hong and their colleagues. “Using these contacts, we fabricate a tungsten disulfide (WS₂) photodiode with a photoresponsivity of 0.29 A W⁻¹, linear dynamic range of 122 dB and power conversion efficiency of 9.9%.”

As part of their recent study, the researchers integrated the conductive-bridge interlayer contacts they developed in a WS₂-based photodiode. They found that this interlayer effectively reduced undesirable electronic interactions, such as Fermi level pinning, thus improving the photodiode’s power conversion efficiency.

“Our approach also provides a platform for probing photocarrier dynamics, and we find that contact recombination substantially affects PV performance,” wrote Jang, Hong and their colleagues. “In addition, we illustrate the potential of using photodiodes with these conductive-bridge interlayer contacts as full-color two- and three-dimensional imagers.”

In the future, the new conductive-bridge interlayer contacts developed by this team of researchers could be integrated and tested on other 2D semiconductor-based optoelectronic devices. Ultimately, they could contribute to the advancement of a wide range of technologies, including communications, imaging and sensing systems.

© 2025 Science X Network