Sensitive Room Temperature THz Detectors

Intro to THz detector technology

Terahertz (THz) frequency band offers many unique opportunities, such as applications in security screening, bio, medical, pharmaceutical industry. However, lack of affordable and sensitive room temperature detectors for the THz band hinders the development of the various technologies.

Related previous research by Sherwin group

77 K UCSB Terahertz Antenna Coupled Inter-subband Terahertz (TACIT) Detector Previously, Sherwin group had made a sensitive narrowband, tunable Terahertz detector based on inter-subband transition of quantum wells. However, due to the nature of its excitation mechanism, it required cooling with liquid Nitrogen.

Beginning of the 300 K UCSB THz detector project

Using similar device structure to the TACIT at 77K, but by introducing a non-saturable absorber instead of inter-subband transitions of the quantum wells, we could make room temperature THz detectors. One such example is bulk electron plasmon.
Absorb THz with twin-slot dipolar antennas --> transfer the energy into active area of the transistor --> excite 3D electrons --> measure the change of Source-Drain resistance. The antenna was designed to work for horizontally polarized THz radiation. A photoconductive signal was expected.

Recent experimental results

In experiments, however, our detector responds to vertical polarization only (at 300 K), and generates photovoltaic signal. E&M simulation later showed that we are indeed coupling to the vertical polarization via “surface plasmonic mode” supported by metal-insulator-metal gaps in our unique detector structure. The resulting responsivity from this unexpected detection mode is better than commercial pyroelectric detectors, but not better than Schottky diodes, the current state-of-the-art.
These results are published on Appl. Phys. Lett. 92, 253508 (2008). Here are the data (pdf), from which we reason that the responsivity is due to excitation of 3D electron plasmon.

Search for detection mechanisms

Although our detector works, the exact operating principle is not understood. Theoretical and experimental exploration for possible detection mechanism is ongoing.

Next generation devices

Design and fabrication of next generation devices is ongoing.

Figure: UCBS THz detector sees the water absorption through 60 cm of air in the lab.