Integration of multi-layer black phosphorus into photoconductive antennas for THz emission

Abstract

We report the fabrication, characterization, and modeling of photoconductive antennas (PCAs) using 40 nm thin-film flakes of black phosphorus (BP) as the photoconductor and hexagonal boron nitride (hBN) as a capping layer to prevent oxidation of BP. Dipole antennas were fabricated on oxidized high-resistivity Si substrates, and BP and hBN flakes were picked up and transferred onto the antenna inside a nitrogen glovebox. The transfer matrix technique was used to optimize the thickness of BP and hBN for maximum absorption. BP flakes were aligned with the armchair axis along the anode–cathode gap of the antenna, with crystal orientation measured using reflection anisotropy. Photocurrent imaging under illumination with 100 fs pulses at 780 and 1560 nm showed a bias-dependent maximum photocurrent localized to the antenna gap with a peak photoconductivity of 1 (2) S/cm in the linear regime of bias for excitation at 780 (1560) nm. Photocurrent saturation in bias (pump fluence) occurred at approximately 1 V (0.25mJ/cm2). Device performance was modeled numerically by solving Maxwell’s equations and the drift–diffusion equation to obtain the photocurrent density in response to pulsed laser excitation, which was largely in qualitative agreement with the experimental observations. THz output computed from surface current density suggests that BP THz PCA performance is at least comparable to more traditional devices based on low-temperature-grown GaAs. These devices represent a step toward high-performance THz photoconductive antennas using BP.

Experimental and Computational Analysis of Broadband THz Photoconductive Antennas

“…Te other two modules are the semiconductor module to solve the difuse/drift equations and the RF transient to solve the radiation equation. To avoid repeating the details of the three modules, we refer the readers to the cited references [11,13,25].…”

“…Te results demonstrate that the generated photocurrent densities are approximately the same in all four devices, as expected since they have the same dimensions of the antenna gap and the thickness of the LT-GaAs layer. A variety of aspects of simulations and boundary conditions used in the COMSOL model can be seen in Appendix A and in [10,11,13,17,25].…”

“…To connect the bias voltage to the electrodes, an aluminum (Al) wire bond of diameter 1 mil is used as shown in Figure 13. "Te design of the device was accomplished using a COMSOL Multiphysics model based on several eforts reported in [1,10,11,13,17,25]. "…”

Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials

“…They observed a strong absorption of 36% at 780 nm, which suggests a promising outlook for the THz performance of these devices. 45 Additionally, computational work by Sibari and collaborators explores the relation among atomistic structure and electronic properties of few-layer black phosphorene, 46 while Betancur-Ocampo and coworkers employed a Green's function formalism on a tight-binding model of a black phosphorus monolayer pnp junction, as well as a continuum description, and determine that these junctions operate as electron waveguides. 47…”

Photonic Platforms Using In‐Plane Optical Anisotropy of Tin (II) Selenide and Black Phosphorus

“…[2,3] Here, we focus on 2D materials that are substantially triaxial, with low optical symmetry within individual layers. [4,5] Among layered and 2D materials, there are many with substantial optical anisotropy within individual layers, including the group-IV monochalcogenides MX (M ¼ Ge or Sn and X ¼ S or Se) and black phosphorous (bP). We study whether the optical anisotropy within individual layers can be used to switch light in PIC devices, provided that a mechanism is available to switch the crystal orientation (i.e., the domain pattern).…”