Previously, members of the Sherwin Group made a sensitive narrowband, tunable terahertz (THz) detector based on intersubband transitions of quantum wells. However, due to the nature of its excitation mechanism, it required costly liquid nitrogen cooling. With a device structure similar to that of the previous detector, but by introducing bulk electron plasmon as an absorber, a sensitive broadband, room temperature terahertz detector is realized. In this work, the plasmons in GaAs metal-semiconductor-field-effect-transistors (MESFETs) have been electrically tuned and detected for frequencies of 0.14, 0.24, 0.6 and 1 THz. The first generation of these detectors exhibits sensitivity and speed characteristics better than those of commercial pyroelectric detectors (measured responsivity of 80 μA/W, a NEP of about 50 nW/Hz1/2 , and speed < 10 ns). Although the detector works well, numerous unexpected behaviors were observed, such as strong photovoltaic response and dual resonances. These observations are explained with the assumption of two space-charge regions where plasmons are locally excited and a terahertz self-rectification process occurs. The new analytical model of “plasmon-assisted self-mixing” can explain the experimental observations both qualitatively and quantitatively. Also, the model suggests three important factors for improving the detector sensitivity: power coupling efficiency, self-mixing efficiency, and the plasma resonance. If carefully optimized, the performance of this new detection scheme could rival that of the commercial state-of-the-art Schottky diode detectors. The new detection scheme also conceptually permits scaling to higher frequencies without the significant loss of sensitivity exhibited by Schottky diodes. Therefore, it would be interesting to navigate the possibility of terahertz to mid-infrared (MIR) operation or waveguide coupling where the technology could be integrated with various quantum cascade lasers (QCLs). Successful detectors may be employed to characterize THz-QCLs, or could become compact receiver parts for a terahertz communication system or pixels for a focal plane array terahertz imager.
|Advisor:||Sherwin, Mark S.|
|Commitee:||Cleland, Andrew, Gossard, Arthur C., Lubin, Phillip|
|School:||University of California, Santa Barbara|
|School Location:||United States -- California|
|Source:||DAI-B 70/11, Dissertation Abstracts International|
|Subjects:||Electrical engineering, Electromagnetics, Condensed matter physics|
|Keywords:||Detection, Field effect transistors, Gallium arsenide, Plasmon-assisted self-mixing, Self-mixing, Terahertz|
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