Nanoslit cavity plasmonic modes and built-in fields enhance the CW THz radiation in an unbiased antennaless photomixers array

Abstract

A new generation unbiased antennaless CW terahertz (THz) photomixer emitters array made of asymmetric metal-semiconductor-metal (MSM) gratings with a subwavelength pitch, operating in the optical near-field regime, is proposed. We take advantage of size effects in near-field optics and electrostatics to demonstrate the possibility of enhancing the THz power by 4 orders of magnitude, compared to a similar unbiased antennaless array of the same size that operates in the far-field regime. We show that, with the appropriate choice of grating parameters in such THz sources, the first plasmonic resonant cavity mode in the nanoslit between two adjacent MSMs can enhance the optical near-field absorption and, hence, the generation of photocarriers under the slit in the active medium. These photocarriers, on the other hand, are accelerated by the large built-in electric field sustained under the nanoslits by two dissimilar Schottky barriers to create the desired large THz power that is mainly radiated downward. The proposed structure can be tuned in a broadband frequency range of 0.1-3 THz, with output power increasing with frequency.

Significant performance improvement of a terahertz photoconductive antenna using a hybrid structure

“…3c, the plasmonic resonance mode between two adjacent nanostructures is responsible for high photocurrent peak at periodicity of 190 nm that is the same phenomena seen at ref. 34. By increasing the periodicity parameter, as can be observed in Fig.…”

Analysis of Screening Effects on Terahertz Photoconductive Devices Using a Fully-Coupled Multiphysics Approach

“…Ignoring the source term J t c (r, t) in ( 3) (as done with the methods described in [21], [33]- [35]) has two consequences in terms of modeling screening effects: (i) As described in Section I and in [20], [21], the increasing photoconductivity limits the penetration of the optical EM fields into the active region of the device, resulting in optical-field screening. If J t c (r, t) in ( 3) is ignored, the EM fields do not "see" the effective photoconductivity and therefore the optical-screening cannot be account for.…”

“…(ii) "Uncoupled" simulation that uses the same mathematical model except J t e (r, t) and J t h (r, t) are ignored. The uncoupled simulation is similar to the frequency-domain FEM-based approach [21], [33]- [35] where the EM fields are computed by the Maxwell solver without taking into account the photocurrents (the screening effects are ignored). Since in the unit-cell model, the source aperture is assumed infinitely large, in the following, the peak power flux density S pump (in unit of mW/cm 2 ) is used as a measure of the optical pump power.…”

“…These approaches use semianalytical expressions of the generation rate and do not strictly model the two-way coupling between the EM fields and the carriers [26]- [32]. In recent years, the finite element method (FEM), which is more flexible and accurate than FDM, has started to become the method of choice to compute the optical EM fields, especially on nanostructured PCDs [21], [33]- [35]. But like the previous approaches, those that rely on FEM ignore the coupling from the carriers to the EM fields and therefore they cannot account for the screening effects [21].…”

Analysis of Screening Effects on Terahertz Photoconductive Devices using a Fully-Coupled Multiphysics Approach

“…These approaches use semi-analytical expressions of the generation rate and do not strictly model the two-way coupling between the EM fields and the carriers [26][27][28][29][30][31][32]. In recent years, the finite element method (FEM), which is more flexible and accurate than FDM, has started to become the method of choice to compute the optical EM fields, especially on nanostructured PCDs [21,[33][34][35]. But like the previous approaches, those that rely on FEM ignore the coupling from the carriers to the EM fields and therefore they cannot account for the screening effects [21].…”