Novel Terahertz Emitters and Detectors: InGaAs Slot Diodes and InAs Self-Switching Diodes

Licentiate thesis, 2013

Two novel types of diodes for emission and detection of THz radiation have been investigated. The diodes are based on high electron mobility III-V heterostructures. Both diodes are aimed for room-temperature operation, for which there is a demand for new THz technology. For emission, slot diodes based on an InGaAs heterostructure were studied. Slot diodes have been proposed as a potential power source at terahertz frequencies. However, slot diodes have never been demonstrated experimentally, only in Monte Carlo (MC) simulations. In this thesis, design, fabrication and I-V characterization of slot diodes are covered, as well as emission experiments. Despite the fact that MC simulations predicted an output power of 50 µW at 0.8 THz or higher, no emission was detected for the fabricated slot diodes experimentally up to 1 THz with a noise floor of 10 nW. For detection, InAs self-switching diodes (SSDs) for zero-bias operation were investigated. Fabrication, design and characterization of InAs SSDs are presented. Responsivity was measured on-wafer in the range 2-315 GHz, for which no roll-off was observed. At 50 GHz, the InAs SSD showed a responsivity of 17 V/W and noise-equivalent power (NEP) of 150 pW/Hz½ when driven by a 50 Ω source. With a conjugately matched source a responsivity of 34 V/W and NEP of 65 pW/Hz½ are expected, based on s-parameters and responsivity as measured with a 50 Ω source. An InAs SSD designed with a substrate antenna demonstrated detection in a free-space experiment at 600 GHz. For comparison, InGaAs SSDs which are a more established type of SSDs were evaluated. For InGaAs SSDs, a lowest NEP of 65 pW/Hz½ with a 50 Ω source was achieved, measured at 50 GHz. The measured responsivity was 280 V/W. It was observed that DC measurements can be used to successfully predict responsivity and NEP of SSDs. Also, the first systematic experimental study of how the design influences the SSD detection performance was carried out.