Integration of Multi-layer Black Phosphorus into Photoconductive Antennas for THz Emission

We fabricated, characterized, and modeled photoconductive antennas by using black phosphorus (BP; ~ 40 nm thin film as the photoconductor) and hexagonal boron nitride (hBN; a capping layer to prevent the oxidation of BP). BP and hBN flakes were transferred inside a nitrogen glovebox onto dipole antennas (fabricated on oxidized high-resistivity Si substrates). The thickness of the BP and hBN were optimized for maximum absorption within the BP layer using the transfer matrix method. The armchair axis of BP flakes (determined by reflection anisotropy) was aligned with the anode-cathode gap of the antenna. Under illumination with 100 fs pulses at 780 (1560) nm, photocurrent imaging shows a bias-dependent maximum photocurrent localized to the antenna gap with a peak photoconductivity 1 (2) S/cm in the linear regime of bias [1]. Device performance was modeled numerically by solving Maxwell’s and the drift-diffusion equations to obtain the photocurrent density in response to pulsed laser excitation, showing qualitative agreement with the experimental observations. These devices present a step toward high-performance THz photoconductive antennas using BP.

[1] Doha, M. H. et al. (2020). J. Appl. Phys, 128(6), 063104.