Electron Tunneling Enhances Thermal Conductance through Metal-Insulator-Semiconductor Junctions

Abstract

The presence of interfaces in semiconductor devices substantially hinders thermal transport, contributing disproportionately to the overall thermal resistance. However, approaches to enhance interfacial thermal transport remain scarce without changing the interface structure, as the intrinsic electron and phonon properties of constituent materials set an upper limit. Here, we find a new thermal transport pathway, electronic heat tunneling, to enhance interfacial thermal conductance through metal-insulator-semiconductor junctions. By applying photoexcitation or bias voltage, we observe remarkable thermal conductance increases in operando, opening a new channel for efficient interfacial heat dissipation. The electron quantum tunneling pathway is parallel to conventional phonon-mediated interfacial thermal transport, and violates the Wiedemann-Franz law since this pathway deviates from the paradigm of diffusive transport. Moreover, we develop a tunneling mismatch model to describe the enhanced thermal conductance, originating from tunneling heat flux. Our Letter demonstrates a previously unexplored heat transport mechanism to enhance thermal conductance, bypassing the need for interface engineering. These findings emphasize the essential need to understand semiconductor thermal properties under realistic operating conditions.

Figures (4)

• Figure 1: (a) Schematic illustration depicting the experiment in the Al-SiO$_2$-Si MIS junction under continuous-wave laser excitation. (b) TDTR signals acquired at varying photoexcited electron concentrations. The experimental signals (open circles) were fitted using a multilayered heat diffusion model (solid lines). Red symbols correspond to signals obtained without excitation, while purple and blue symbols correspond to signals under electron concentrations n of 2.84$\times$10$^{19}$ cm$^{-3}$ and 6.34$\times$10$^{19}$ cm$^{-3}$, respectively.
• Figure 2: Measured thermal conductance of the Al/SiO$_2$/Si interface in the MIS junction. Data points corresponding to 532 nm, 671 nm, and 808 nm laser excitation are represented by green, blue, and red circles, respectively. The dashed gray line denotes thermal conductance in the absence of excitation. The inset figure shows band profiles of the MIS junction under continuous-wave excitation, where $\Phi$ denotes the effective barrier height of the SiO$_2$ layer, E$_f$ is the Fermi energy, and E$_{exc}$ represents elevated electron energy by photoexcitation.
• Figure 3: Primary pathways for heat flow across the metal/insulator/semiconductor interface in our experiment. R$_{et}$, R$_{ep}$, and R$_{pp}$ represent interfacial thermal resistance of electron tunneling, electron-phonon interactions, and phonon-phonon interfacial thermal transport, respectively.
• Figure 4: (a) Schematic illustration depicting the experiment in the Al-thin SiO$_2$-doped Si MIS junction under bias voltages, where the voltage source shows the bias direction. (b) Measured thermal conductance of the Al (or Au)/SiO$_2$/doped Si interface (filled circles) at 300 K, fitted by the tunneling mismatch model (dashed lines). The red plots represent thermal conductance measured in the Al-SiO$_{2}$-doped Si junction (4.58$\times$10$^{19}$ cm$^{-3}$). Blue plots show the measurements in the Al-SiO$_{2}$-doped Si junction (1.03$\times$10$^{20}$ cm$^{-3}$), while orange plots display measurements in the Au-SiO$_{2}$-doped Si junction (4.58$\times$10$^{19}$ cm$^{-3}$). The inset figure shows band profiles of the MIS junction under bias, where U stands for the voltage.