Deep Level Transient Spectroscopy Reveals Influence of Defects on 2D Semiconductor Devices

By using deep level transient spectroscopy (DLTS), researchers can learn more about potential defects in the electrical properties of two-dimensional (2D) semiconductors, according to a new study published in Nature Communications (1).

Semiconductor analysis is increasingly becoming a hot topic in spectroscopy circles. In particular, semiconductors are used for many clean energy products, including self-driving vehicle circuits and solar cells (2). Because semiconductors are so vital to powering many electronic devices and other essential equipment, their production is important to ensure a thriving society. It is also important to ensure that the materials used to construct semiconductors are of optimal condition to prevent any defects with their electrical properties.

Vibrational spectroscopic techniques have been used in the past to characterize, optimize, and analyze semiconductor materials (2). In this study, researchers from the Institute of Electrical and Microengineering in Lausanne, Switzerland, delved into analyzing 2D semiconductors and their electrical defects (1). Led by Andras Kis, the research team’s findings provided insight on how to innovate the next generation of electronic devices and integrate them into practical applications (1).

Defects in solid materials are inevitable and can significantly alter their electronic and optical characteristics of semiconductors. With the rapid advancement in the utilization of 2D semiconductors, understanding and characterizing the effects of defects has become increasingly important (1). Using DLTS, the research team examined the electrical response of defect filling and emission in monolayer metal-organic chemical vapor deposition (MOCVD)-grown materials deposited on complementary metal-oxide-semiconductor (CMOS)-compatible substrates (1).

Through aberration-corrected scanning transmission electron microscopy (STEM) imaging and theoretical calculations, the researchers identified that neighboring sulfur vacancy pairs introduce additional shallow trap states through the hybridization of individual vacancy levels (1). These vacancy pairs are important because they have a great influence on the off currents and switching slopes of field-effect transistors based on 2D semiconductors (1).

As part of their study, the researchers focused on locating a shallow state that emerges through the hybridization of the neighboring sulfur vacancy pairs. They accomplished this by using DLTS and adapting it to single-layer MOCVD-grown molybdenum disulfide (MoS2) crystals using CMOS-compatible device geometry (1). DLTS also helped detect energy linewidths. Doing so helped them confirm the narrow bandwidth of the hybridized shallow state and considerable energy broadening of vacancy-sulfur traps (1).

The high sensitivity of DLTS measurements and its applicability to capacitor-based devices offer a pathway for understanding atomic defects and their electrical properties in 2D semiconductors. Based on the results of this study, the researchers anticipate that the future application of DLTS techniques in other 2D materials will be able to accomplish three objectives. First, they will enrich the defect library; second, they will unveil unexplored defect characteristics; and finally, DLTS technologies will facilitate effective defect engineering and mitigation (1).

As 2D materials continue their rapid progress towards electronic device applications, the DLTS technique stands poised as an efficient tool for defect characterization and device enhancement.

References

(1) Zhao, Y.; Tripathi, M.; Cernevics, K.; et al. Electrical Spectroscopy of Defect States and the Hybridization in Monolayer MoS2.Nat. Commun. 2023, 14, 44. DOI: 10.1038/s41467-022-35651-1

(2) Dahal, S. Using Raman Spectroscopy for Semiconductor Analysis. Available at: https://www.thermofisher.com/blog/materials/?p=13939 (accessed 2024-04-25).