Enhanced near-field thermal radiation between black phosphorus with high electron density by BP/hBN heterostructures

The black phosphorus (BP)/hexagonal boron nitride (hBN) Van der Waals heterostructure has great potential application in BP-based devices due to its higher stability than monolayer BP film. The near-field thermal radiation (NFTR) between two identical BP/hBN heterostructures with high electron density is studied to promote the application of BP-based devices. The BP/hBN heterostructures show a higher heat transfer coefficient (HTC) at a 10 nm gap distance compared to BP films with electron density n larger than 1 × 1013 cm−2, due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). Especially at n ≥ 3 × 1013 cm−2, the improvement is more than 100%. The SPPs and the HPPs couple into surface plasmon-phonon polaritons (SPPPs) out of the hyperbolic region and hyperbolic plasmon-phonon polaritons (HPPPs) inside. The SPPPs can achieve photon tunneling in the broader wavevector region than SPPs, making most of the contribution to heat transfer. The influences of the thickness of the hBN sheet and gap distance are also discussed. This scheme only effectively enhances NFTR for BP with high electron density at small nanogaps. After structural optimization, h = 2 nm is the optimal thickness for BP/hBN configuration with low electron density, such as n = 1 × 1013 cm−2. In contrast, large thickness h = 500 nm is optimal for BP with high electron density. At high electron density, a thick hBN sheet is prominent in enhancing the SPPPs in the frequencies below the type-I region and the HPPPs inside the type-II region. We further propose BP/hBN/BP heterostructures and find that HTC is further enhanced by 4.4% ~ 30.8% due to the more robust surface modes. Our work may contribute to developing BP-based near-field thermal devices and promote understanding the NFTR mechanism of BP/hBN heterostructure.