In the world of semiconductor nanodevices, where quantum effects and atomic positions dictate behavior, the demand for advanced characterization methods is on the rise, and spectroscopic techniques emerge as powerful tools to unlock their quantum properties and explore their unique dimensions.
Image Credit: noisuk Photo/Shutterstock.com
Semiconductor nanodevices are prized for their size-dependent properties and the potential control offered by the semiconductor structures. Objects on the nanometer length scale often have very large surface area to volume ratios and quantum effects often dominate the behavior and response of the nanodevice. The highly controllable, size-dependent properties of semiconductor nanodevices have seen them used in a number of application areas, from energy storage, optoelectronics and pharmecuticals.1
As the properties of a semiconductor nanodevice can be dependent on the positions of individual atoms in the structure and the devices are highly sensitive to their dimensions and architecture, developing semiconductor nanodevices is highly demanding in terms of characterization techniques.
The growing interest in nanodevices and advances in nanofabrication methods make it possible to create new architectures, which means that demand for such advanced characterization methods is also increasing.
Spectroscopic methods are one such approach for semiconductor nanodevice characterization and analysis and are powerful tools for both physical characterization of the dimensions and shape of such semiconductor nanodevices as well as for the exploration of their quantum properties and behaviour.2,3
Overview of Semiconductor Nanodevices
There is a growing range of semiconductor nanodevice shapes and structures available, from simpler nanowires to more complex architectures that can be used to produce light emitting diodes (LEDs) and lasers.4
What makes semiconductor nanodevices so interesting in terms of applications is that, at the small length scale of these devices, the electron transport is largely ballistic and the electrons travel without experiencing collisions.5
In a standard, macroscale electronic device or semiconductor, electron collisions are relatively frequent, leading to energy loss, heating and a loss of information. In semiconductor nanodevices, the electron transport is more akin to that of an electromagnetic wave and so quantum coherence effects can be exploited in the device.
This is why, as well as trying to develop new devices for applications, another big challenge has been finding how to use spectroscopic techniques to measure the electron transport properties and using modeling to understand how the material structure affects the electron decoherence times.6
Spectroscopy Techniques
Spectroscopic methods have been used extensively in the material sciences for characterization, with applications in semiconductor nanodevices. The availability of sub-nanometer resolution techniques has been an essential part of device development. Popular techniques for studying semiconductor nanodevices include terahertz spectroscopy, scanning tunneling electron microscopy and Raman spectroscopy.7-10
Electron microscopes are useful for semiconductor nanodevice analysis as their high spatial resolution makes it possible to image and, with the right reconstruction algorithms, even reconstruct full 3D structures of the nanodevice. The structural analysis is essential for confirming device dimensions and geometry. Tunneling microscopy methods are also useful as they can be adapted for device fabrication but also as a way of measuring the spatially localized electron forces in the device.
Many semiconductor nanodevice studies now make use of electron microscopy in combination with another spectroscopic technique, such as optical or terahertz spectroscopy, for spatially resolved analysis of properties such as optical absorption strength.11
Raman spectroscopy can be a useful tool for the chemical analysis of semiconductor nanodevices but also to look at their phonon transport properties and any physical strain in the device.12 Phonon motion can be one of the processes that lead to the destruction of electronic coherences and, if the device application requires the preservation of quantum coherence, say for information transfer, can be problematic.
Terahertz spectroscopy is a very versatile and useful tool for understanding semiconductor nanodevice functioning. While there are many experimental complexities to performing terahertz measurements, the ability to directly measure the charge carrier dynamics in semiconductor devices is an incredibly powerful tool in understanding how to refine their design.
Advantages and Challenges
Terahertz and Raman spectroscopy are both nondestructive techniques, though electron microscopy and exposure to intense electron beams can lead to sample degradation and damage. The key advantages of using spectroscopy methods are the sensitivity to many of the quantum scale phenomena happening in semiconductor nanodevices and the ability to selectively probe phenomena such as the phonon motion or charge carrier dynamics. Most spectroscopy techniques work well at the nanoscale.
One challenge for device measurements is that some techniques require a certain amount of sample preparation or it can be difficult in many instruments to perform true in operando measurements. Terahertz radiation can be challenging to generate and there are still limited numbers of optics and detectors that work well in these wavelength regions. Most of these techniques still require an expert user, in particular for the interpretation of data, and instrumentation can be prohibitively expensive, particularly for electron microscopy.
Conclusion
However, despite the challenges, spectroscopic techniques have helped make huge advances in our understanding of how nanoscale semiconductors work and how they differ from their more macroscopic counterparts.
The understanding of the atomic-level behavior and quantum effects in semiconductor nanodevices provided by spectroscopic measurements is an essential part of learning how these devices work and how their structures and elemental compositions can be tuned for particular properties.
See More: How to Make a Semiconductor Wafer
References and Further Reading
Tertis, M., Cernat, A., Mirel, S., & Cristea, C. (2021). Nanodevices for Pharmaceutical and Biomedical Applications Nanodevices for Pharmaceutical and Biomedical. Analytical Letters, 54(1–2), 98–123. https://doi.org/10.1080/00032719.2020.1728292
Hirsch, O., Kvashnina, K., Willa, C., & Koziej, D. (2017). Hard X ‑ ray Photon-in Photon-out Spectroscopy as a Probe of the Temperature-Induced Delocalization of Electrons in Nanoscale Semiconductors. Chemistry of Materials, 29, 1461–1466. https://doi.org/10.1021/acs.chemmater.6b05218
Ibabe, A., Gómez, M., Steffensen, G. O., Kanne, T., Nygård, J., Yeyati, A. L., & Lee, E. J. H. (2023). Joule spectroscopy of hybrid superconductor – semiconductor nanodevices. Nature Communications, 14, 2873. https://doi.org/10.1038/s41467-023-38533-2
Li, J., Wang, D., & LaPierre, R. R. (Eds.). (2011). Advances in III-V semiconductor nanowires and nanodevices. Bentham Science Publishers.
Gross, P., Ramakrishna, V., Vilallonga, E., Rabitz, H., Littman, M., Lyon, S. A., & Shayegan, M. (1994). Optimally designed potentials for control ofelectron-wave scattering in semiconductor nanodevices. Physical Review B, 49(16), 100–110. https://doi.org/https://doi.org/10.1103/PhysRevB.49.11100
Querlioz, D., Saint-Martin, J., Bournel, A., & Dollfus, P. (2008). Wigner Monte Carlo simulation of phonon-induced electron decoherence in semiconductor nanodevices. Physical Review B, 78, 165306. https://doi.org/10.1103/PhysRevB.78.165306
Lundh, J. S., Zhang, T., Zhang, Y., Xia, Z., Wetherington, M., Lei, Y., Kahn, E., Rajan, S., Terrones, M., & Choi, S. (2020). 2D Materials for Universal Thermal Imaging of Micro- and Nanodevices: An Application to Gallium Oxide Electronics. Applied Electronic Materials, 2. https://doi.org/10.1021/acsaelm.0c00574
Peng, W., Wang, H., Lu, H., Yin, L., Wang, Y., Grandidier, B., Yang, D., & Pi, X. (2021). Recent Progress on the Scanning Tunneling Microscopy and Spectroscopy Study of Semiconductor Heterojunctions. Small, 17, 2100655. https://doi.org/10.1002/smll.202100655
Vianez, P., Tsyplyatyev, O., & Ford, C. (2021). Semiconductor nanodevices as a probe of strong electron correlations. https://doi.org/10.1016/B978-0-12-822083-2.00007-1
Ho, I., & Zhang, X. (2014). Application of broadband terahertz spectroscopy in semiconductor nonlinear dynamics. Front. Optoelectron., 7(2), 220–242. https://doi.org/10.1007/s12200-014-0398-2
Wieghold, S., & Nienhaus, L. (2020). Probing Semiconductor Properties with Optical Scanning Tunneling Microscopy. Joule, 4(3), 524–538. https://doi.org/10.1016/j.joule.2020.02.003
Anaya, J., Torres, A., Martín-martín, A., Martínez, O., Prieto, A. C., & Jiménez, J. (2010). Raman spectroscopy study of group IV semiconductor nanowires. Physics Procedia, 8, 78–83. https://doi.org/10.1016/j.phpro.2010.10.015
