A method for reducing the reflections from silicon optics at terahertz frequencies has been investigated. In this study, we used thin films of parylene as an anti-reflection (AR) layer for silicon optics and show low-loss behavior well above 1 THz. Transmittance spectra are acquired on double-sided-parylene-coated, high-resistivity, single-crystal silicon etalons between 0.45 THz and 2.8 THz. Modeling the optical behavior of the three-layer system allowed for the determination of the refractive index and absorption coefficient of parylene at these frequencies. Our data indicate a refractive index, , of 1.62 for parylene C and parylene D, and a reasonably modest absorption coefficient make these materials a suitable AR coating for silicon at terahertz frequencies. Coatings sufficiently thick for AR performance reduced the average transmittance of the three-layer system by 10% compared to a lossless AR coating with an ideal refractive index.

Microwave mixing and noise measurement techniques have been used to characterize energy relaxation and noise phenomena for the two-dimensional electron gas (2DEG) medium in single AlGaAs/GaAs modulation-doped quantum wells. Mixing experiments at 94 GHz yield the energy relaxation time directly, in good agreement with optical methods previously reported. The noise output power at low microwave frequencies (1.5–3.5 GHz), is shown to have one term due to Nyquist noise at the electron temperature, and a second frequency-dependent term caused by fluctuations in the electron temperature.

This paper presents a new type of electron bolometric ("hot electron") mixer. We have demonstrated a three order of magnitude improvement in the bandwidth compared with previously known types of electron bolometric mixers, by using the two-dimensional electron gas (2DEG) medium at the hetero-interface between AlGaAs and GaAs. We have tested both in-house MOCVD-grown material, and MBE material, with similar results. The conversion loss (L ,) at 94 GHz is presently 18 dB for a mixer operating at 20 K, and calculations indicate that L, can be decreased to about 10 dB in future devices. Calculated and measured curves of L, versus &o, and IDC, respectively, agree well. We argue that there are several different configurations of electron bolometric mixers, which will all show wide bandwidth, and that these devices are likely to become important as low-noise THz receivers in the future.

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