Modeling of interfacial phonon transport and electron-phonon interactions for thermal management in micro/nano-electronics
Creators: name: Huang, Xu
Publisher: name: No Publisher Supplied
Year: 2022

description: High thermal conductivity electronic components with low interfacial thermal resistance are of technological importance and fundamental interest of research. Diamond and cubic polymorph of boron nitride (c-BN) are two promising ultrawide bandgap semiconductor materials owning superior thermal properties. Silicon is the most commonly used semiconductor. In this dissertation, we firstly employed ab initio calculation of phonon transport to investigate lattice vibrations and thermal properties of the above-mentioned three materials. Heat transport phenomena across the interfaces of Si/diamond, c-BN/diamond, and Si/c-BN are unfolded. The interfacial thermal conductance of c-BN/diamond is found to be ten-fold of that of Si/diamond; besides, the thermal conductance across Si/c-BN interface is 20.2% larger than that of Si/diamond at 300 K and 18.9% larger at 340 K.The rapid development of GaN-on-diamond devices holds much promise for thermal management of high-power electronics and devices. Hitherto, the interfacial effect of an inherent epilayer between GaN and diamond to thermal dissipation is less investigated. The second aim of this dissertation is to understand and analyze the thermal boundary resistance (TBR) across a diamond/GaN heterostructure with the presence of an epilayer of either AlN, or Si₃N₄, or Si. Based on the first-principles calculation, we found that the Si₃N₄ epilayer gave the lowest TBR at 4.58 m²K/GW among the three epilayer types in diamond/GaN interface when the epilayer is 5 nm thick. We also revealed the epilayer thickness effect and found that the lowest TBR exists for the AlN epilayer around 50 nm thickness and for the Si₃N₄ epilayer around 70 nm thickness. The interfacial TBR reduced when the diamond cap or the GaN substrate was replaced by the c-BN. Further, c-BN can be directly grown on diamond without use of epilayer, resulting in an unprecedented low TBR of 0.4 m²K/GW in the diamond/c-BN interface. Although lattice vibration is the dominant mechanism of heat conduction in semiconductors, electron-phonon interactions exist and may affect phonon transport in doped semiconductors; yet such effects in wide bandgap materials have not received much attention. The third aim of this dissertation is to explore the effects of electron-phonon interactions on the lattice thermal conductivity and phonon transport in doped Si, diamond, and c-BN under various electron concentrations and in a wide temperature range from 300 K to 900 K based on the first-principles calculation. It is found that the electron-phonon interactions will bring down the thermal conductivity of doped materials, and the depletion impact increases as the electron concentration increases but decreases as the temperature increases. This depression effect in ultrawide bandgap diamond and c-BN is apparent, though it is not as severe as in Si. At room temperature with a high electron concentration of 10²¹ cm⁻³, the reduction of thermal conductivity reaches 36% in Si, and 17.4% and 16.1% in diamond and c-BN, respectively. The findings in this dissertation provide us new vision and potential solution to heat dissipation of electronic devices, shedding light on future thermal management of c-BN and diamond related electronics.