Picosecond transient thermoreflectance for thermal conductivity characterization

ABSTRACT

We developed a picosecond transient thermoreflectance (ps-TTR) system for thermal property characterization, using a low-repetition-rate picosecond pulsed laser (1064 nm) as the heating source and a 532 nm CW laser as the probe. Low-repetition-rate pump eliminates the complication from thermal accumulation effect. Without the need of a mechanical delay stage, this ps-TTR system can measure the thermal decay curve from 500 ps up to 1 ms. Three groups of samples are tested: bulk crystals (glass, Si, GaAs, and sapphire); MoS₂ thin films (157 ~ 900 nm thickness); InGaAs random alloy and GaAs/InAs digital alloy (short period superlattices). Analysis of the thermoreflectance signals shows that this ps-TTR system is able to measure both thermal conductivity and interface conductance in nanostructures. The measured thermal conductivity values in bulk crystals, MoS₂ thin films, and InGaAs random alloy are all consistent with literature values. Cross-plane thermal conductivity in MoS₂ thin films does not show obvious thickness dependence. Thermal conductivities of GaAs/InAs digital alloys are smaller than InGaAs random alloy, due to the efficient scattering at interfaces. We also discuss the advantages and disadvantages of this newly developed ps-TTR system comparing with the popular time-domain thermoreflectance system.

KEYWORDS:

• Thermoreflectance
• cross-plane thermal conductivity
• interfacial thermal conductance
• picosecond

Acknowledgments

The authors would like to acknowledge support from National Science Foundation (NASCENT, Grant No. EEC-1160494; CAREER, Grant No. CBET-1351881; and CBET-1707080). Ann Kathryn Rockwell and Seth R Bank also acknowledge support from NSF Grant No. DMR 1508603, and ARO and DARPA under Contract No. W911NF-17-1-0065.

Supplementary Material

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

This work was supported by the Army Research Office [W911NF-17-1-0065]and National Science Foundation [CBET-1351881,CBET-1707080,DMR 1508603,EEC-1160494].