Abstract-Dual-frequency CMOS terahertz detector with silicon-based plasmonic antenna

Ruizhi Huang, Xiaoli Ji, Yiming Liao, Jingyu Peng, Ke Wang, Yue Xu, and Feng Yan

Fig. 1 (a) The schematic illustration of 3D stacked structure of dual-frequency CMOS THz detector and (b) Cross-section of the detector realized in standard CMOS technology.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-16-23250

Multi-frequency Terahertz (THz) detectors have shown great application potentials in THz imaging and sensing systems. For the first time to our knowledge, a novel dual-frequency THz detector with the stacked structure consisting of a silicon-based plasmonic antenna and a metal-based antenna in one compact unit is proposed and fabricated in standard CMOS technology. Compared with the metal antenna, the antenna based on heavy-doped poly-silicon materials enables the detector to excite localized surface plasmon resonance mode, making the effective absorption of the THz waves and thus resulting in the significant responsivity enhancement of the detector. The experimental results show a maximum voltage responsivity up to about 2000 V/W and 450 V/W, while the noise equivalence power is as low as 23 pW/Hz0.5and 110 pW/Hz0.5 for the silicon antenna and metal antenna at the frequency of 220 GHz and 650 GHz, respectively. The presented dual-frequency detector can be easily implemented in a small size in favor of high-density array integration.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Parasitic transport paths in two-well scattering-assisted terahertz quantum cascade lasers

Li Wang, Tsung-Tse Lin, Ke Wang,  Hideki Hirayama,

https://iopscience.iop.org/article/10.7567/1882-0786/ab2b56

Using nonequilibrium Green's functions, possible parasitic paths are identified in two-well scattering-assisted terahertz quantum cascade lasers operating at 3.5 THz. The majority of electrons in the upper laser state can escape through these paths, causing a 66% loss of population inversion at 50 K. Three types of paths are clarified: one is responsible for non-selective injection via LO-phonon scattering, the other two lead to leakages via high-lying states to downstream periods by sequential tunneling. Finally, several ways of suppressing these paths are suggested by having small oscillator strength (<0.3), or employing asymmetric structure.

Abstract-Controlling loss of waveguides for potential GaN terahertz quantum cascade lasers by tuning the plasma frequency of doped layers

Ke Wang, Tsung-Tse Lin, Li Wang, Wataru Terashima and Hideki Hirayama

http://iopscience.iop.org/article/10.7567/JJAP.57.081001

We have analyzed the waveguide loss originating from various doping layers in double metal waveguides for potential GaN-based terahertz quantum cascade lasers (THz QCLs) by theoretical calculations. The optical field can be very well confined in the active QCL region. Average electron densities in the QCL active region and n+ contact layers should be controlled carefully. The loss in the low-frequency range (3 THz) can be minimized by decreasing the electron density in the QCL layer. In the middle- and high-THz-frequency ranges (~3 < f < 15 THz), the absorption by the heavily doped n+ contact layer dominates the waveguide loss. Consequently, the bulk plasma frequency, which is determined by electron density and shows a strong absorption peak, must be tuned to deviate from the target QCL frequency. The waveguide loss plus the cavity mirror loss can be controlled to be as low as ~24 cm−1.