Probing nanoscale thermal transport in a GaAs/AlGaAs heterostructure

Present-day understanding of power dissipation in nanoscale electronic devices has not kept up with advances in their manufacturing. For instance, it typically takes approximately 10 nanoseconds to re-establish thermal equilibrium following a single binary switching event in electronic materials – much longer than the typical timescale of 1 to 10 picoseconds of the electrical transients involved in modern high-frequency electronics. At some hot spots, transient local energy density can be very high, equivalent to a temperature jump of hundreds of degrees, making the system highly non-equilibrium and dynamical.

To better understand heat dissipation in nanoscale electronics, Gorfien et al. investigated the thermal transport in a GaAs/AlGaAs heterostructure by directly monitoring the lattice temperature evolution over time. They conducted a pump-probe study on the sample with ultrafast electron diffraction arranged in standard Reflection High Energy Electron Diffraction (RHEED) geometry. Using both experimental data and numerical simulation, the researchers extracted thermal boundary resistance (TBR) as a function of the laser pumping fluence.

For a moderate pumping fluence, the extracted TBR matched theoretical predictions under the diffusive transport limit. TBR increased for the lowest pumping fluence, which indicates the effect of ballistic transport. As for the highest pumping fluence, the researchers unexpectedly observed a decrease in TBR, which contradicts the expectation of heat transporting slower at higher temperatures.

Gorfien et al. suspect that this decrease may indicate the failure of Fourier’s Law under such highly non-equilibrium and dynamical conditions. In other words, the temperature change within the length scale of a phonon mean free path could become too large for the concept of local temperature and its gradient to be justified.

Source: “Nanoscale thermal transport across an GaAs/AlGaAs heterostructure interface,” by Matthew Gorfien, Hailong Wang, Long Chen, Hamidreza Rahmani, Junxiao Yu, Pengfei Zhu, Jie Chen, Xuan Wang, Jianhua Zhao, and Jianming Cao, Structural Dynamics (2020). The article can be accessed at http://doi.org/10.1063/1.5129629 .