Electronically tunable near-field radiative heat transfer between doped silicon and graphene-covered silicon dioxide

Abstract The key to the micro/nanoscale thermal management of precision instruments is flexibly controlling the heat flux in the near-field following the actual demand. In this paper, a near-field radiative thermal switch (NFRTS) made of the n-type doped silicon (D-Si) and graphene-covered silicon dioxide (SiO2) plates is proposed to achieve the active near-field radiative heat transfer modulation. The radiative heat flux, thermal switching factor, and thermal modulation factor are calculated for different graphene chemical potential values from 0 to 1 eV and D-Si doping concentrations at different vacuum gaps. This is achieved by considering the breakdown voltage of the SiO2, and with the fluctuational electrodynamics and fluctuation-dissipation theorem. The SiO2 is also replaced by the silicon carbide (SiC) in the thermal switch to clarify further the effect of the breakdown voltage on the performance of the NFRTS. In combining the graphene chemical potential value and D-Si doping concentration, it is obtained that the optimal thermal switching factor is 93.5% for a doping concentration of 1018 cm−3 at a 10 nm vacuum gap for SiO2 system when the heat source and heat sink temperatures are 400 K and 300 K, respectively. This is mainly due to the combination of the major angular frequency band of the transmission coefficients for bulk D-Si determined by the doping concentration and the surface mode of the graphene-covered SiO2 modulated by altering the graphene chemical potential value via applying the external voltage bias. Results also reveal that the performance of the NFRTS with SiC substrate is significantly affected and weakened by the limited breakdown voltage of SiC, and almost always worse than that of the NFRTS with SiO2 substrate. This work paves a way for designing the active near-field thermal management devices for simple structures.