n-type Ge/Si antennas for THz sensing

Abstract

Ge-on-Si plasmonics holds the promise for compact and low-cost solutions in the manipulation of THz radiation. We discuss here the plasmonic properties of doped Ge bow-tie antennas made with a low-point cost CMOS mainstream technology. These antennas display resonances between 500 and 700 GHz, probed by THz time domain spectroscopy. We show surface functionalization of the antennas with a thin layer of α-lipoic acid that red-shifts the antenna resonances by about 20 GHz. Moreover, we show that antennas protected with a silicon nitride cap layer exhibit a comparable red-shift when covered with the biolayer. This suggests that the electromagnetic fields at the hotspot extend well beyond the cap layer, enabling the possibility to use the antennas with an improved protection of the plasmonic material in conjunction with microfluidics.

Terahertz subwavelength sensing with bio-functionalized germanium fano-resonators

“…To reduce the standard Si substrate thickness (∼730 µm), an automatic chemical-mechanical polishing process was performed on the back-side of the 200-mm wafer. Further details can be found in section VII and in [14].…”

“…In previous studies, we have presented the sensing capability of semiconductor-based LSPR devices [10,13,14].…”

“…In particular, we have demonstrated sensing by using highly n-doped Ge bow-tie antennas (n-Ge antenna), epitaxially grown on Si, operating in the THz range [14]. The process for obtaining the high doping in the Ge epilayers, necessary to realize quasi metallic transport conditions in the antenna, was optimized to a quality close to that of bulk Ge [14]. Consequently, a further improvement of the resonant antenna performances, i.e.…”

Impact of surface charge depletion on the free electron nonlinear response of heavily doped semiconductors

“…0.8 < λ < 2 µm, and in the mid-infrared (MIR), i.e. 2 < λ < 20 µm [12][13][14][15][16]. Being low-loss high-quality materials that can be compatible with standard microelectronics fabrication processes, and being their optical response tunable through electrical or optical doping, heavily doped semiconductors offer a unique perspective for integrated optical devices in the NIR and in the MIR [17][18][19][20].…”