# Key Roles of Plasmonics in Wireless THz Nanocommunications--A Survey
## 5 Plasmonic THz Wireless Nanoscale Link Components
### THz Band Nanotransceivers
#### 5.2.2 THz Band Receivers  
As far as concerns state of the art THz band receivers, waveguide integrated detectors using GaAs Schottky barrier diodes (SBDs) [143], are considered the most common implementation choice. However, they pose limitations on their size and available bandwidth, and behave poorly at room temperature, as QCLs [144]. Silicon CMOS technology has also been proposed in [145], for equipping oscillators at 870 GHz, and sub-harmonic detectors between 790 and 960 GHz. These structures require power amplifiers implemented with InP or GaN technologies, in order to challenge path losses, such as the InP based high electron mobility transistors (HEMT) amplifiers with 10 dB gain at 640 GHz [146], or GaN, GaAs or InGaAs HEMTs [147; 148; 149]. Unfortunately, all these components require more chip space and they also pose performance limitations when operating above 1 THz.  
As far as concerns plasmon based THz wave detectors, hybrid plasmonic schemes consisting of plasmonic waveguides along with silicon waveguides, all integrated with conventional nanoantenna structures, such as dipole or bowtie antennas are considered to be promising, beyond state of the art approaches. A POH slot waveguide integrated with a bowtie antenna is proposed in [150], as a THz wave detector. In this structure, a taper is used to connect silicon strip waveguide with the electro-optical polymer refilled plasmonic slot waveguide, all integrated with a bowtie antenna. Plasmonic slot waveguides are capable of guiding electromagnetic waves at subwavelength scale modes, thus bypassing the diffraction limit bottleneck of conventional waveguides. Consequently, they are functioning as nanocouplers, and hence they can be used as excellent matching elements with the state of the art on chip sources such as nanoLEDs [151] and nanolasers [152], which are all belong to the quantum emitters family. Recently, plasmon based nanocouplers, such as plasmonic grating couplers [153], plasmonic waveguide tapers [154], and nanoantennas [155] have been proposed for integrating silicon photonic chip components with plasmon based components, providing a promising approach for manufacturing plasmonic integrated circuits (PICs) [156].  
Alternatively, plasmonic internal photoemission detectors (PIPED) structures, which are actually transmitter and receiver packages, monolithically integrated on a common silicon photonic chip platform, have been also proposed in [157], for THz wave signal generation and coherent detection at frequencies of up to 1 THz. Finally, other more novel approaches are related to the employment of a FET operating at THz frequencies (TeraFET), as a THz detector. Specifically in [158], a TeraFET operation with identical radiation amplitudes at the source and drain antennas but with a phase shift induced asymmetry is proposed, based on the principle that a phase difference between THz signals coupled to the gate and source, and gate and drain terminals of a FET accordingly, enhances device plasmonic resonances. Such a TeraFET structure operates between 200-600 GHz band, and could be used for 5G and beyond, communication systems.  
Figure 17: Antenna feedback principle of a DFB laser.