Tabletop Deep-Ultraviolet Transient Grating to Characterize Ultrawide Bandgap Semiconductors

Ultrawide bandgap semiconductors are promising materials for next-generation computer chips, as they exhibit high electron mobilities and high breakdown voltages [1,2]. To integrate these materials into next-generation devices, methods to characterize their charge, spin, and thermal transport properties at the nanoscale are needed. Moreover, understanding and measuring non-diffusive thermal transport at the length scales comparable to phonon mean free paths in semiconductors is crucial for optimizing device performance. Tabletop transient grating (TG) experiments using visible light have been used to probe nanoscale transport in semiconductors – however, to date, this approach has been limited to near-micron-scale heating patterns and to narrow bandgap materials [3]. Extreme-ultraviolet light has been used to create TG patterns as small as 10s of nm using facility-scale light sources [4], but these facilities have limited access, which limits their application for research into novel materials. To probe transport at nanoscale dimensions, we use deep-ultraviolet light to generate TG periods as small as 287nm [5], which are the smallest periods achieved to date using a tabletop laser source. Additionally, the use of deep-ultraviolet light allows for the excitation of ultrawide bandgap semiconductor materials, such as diamond and hexagonal boron nitride. To demonstrate deep-ultraviolet TG, we generate and probe GHz surface acoustic waves to extract the elastic properties of thin gold films. We also measure the effects of carrier density on electron diffusion in diamond, an ultrawide bandgap material that has been difficult to study previously. We use this novel technique to validate new theories of non-diffusive thermal transport in a variety of wide bandgap semiconductor materials at significantly smaller length scales than could be explored previously [5].


[1] Warzoha at al., Journal of Electronic Packaging 143, 020804 (2021)
[2] Tsao et al., Adv. Electron. Mater. 4, 1600501 (2018)
[3] Johnson et al., Phys. Rev. Lett. 10, 025901 (2013)
[4] Bencivenga et al., Science Advances 5, eaaw5805 (2019)
[5] Nelson, et al. Phys. Rev. Appl. Accepted