manufacturable, high throughput process. Currently, In this paper, we present the latest advancements 75 mm diameter InP substrates are used and EBL of sub 50 nm InGaAs/InAlAs/InP High Electron lithography requires less than 1 hour for exposure Mobility Transistor (InP HEMT) devices that have over the wafer. A maximum wafer throughput of 150 achieved extrapolated Fmax above 1 THz. This wafers per week and 100 wafers per week on 100 mm extrapolation is both based on unilateral gain (1.2 diameter wafers would be possible on a single EBL THz) and maximum stable gain/maximum available system. A 2nd key enhancement is the reduction of gain (1.1 THz) extrapolations, with an associated fT of ohmic contact resistance through a higher doped cap 385 GHz. This extrapolation is validated by the layer design coupled with a InAs/InGaAs channel demonstration of a 3-stage common source low noise grown by molecular beam epitaxy. The sheet MMIC amplifier which exhibits greater than 18 dB gain resistance of the epitaxial layers is lowered to 75 at 300 GHz and 15 dB gain at 340 GHz. ohm/sq. (compared to 110 ohm/sq. in the baseline InP HEMT profile) and the mobility was improved to as INTRODUCTION high as 15,000 cmA2N-sec (compared to 12,000 Future systems will extend the need for higher cmA2/V-sec in the baseline InP HEMT profile). A low frequency and bandwidth devices and circuits beyond contact resistance of 0.05 ohm-mm and a high peak current capability and concepts. Rapid development transconductance as high as 2300 mS/mm was and advancement of solid state transistor and MMIC measured at 1V drain bias with a device breakdown technology has pushed extremely high cutoff typically of 2.5V and a maximum drain source voltage frequency and high maximum oscillation frequencies of 2V and good device pinchoff characteristics. (Fmax) in various technologies [1][2][3]. This paper describes the latest advancements of sub 50 nm InP HEMT DEVICE MEASUREMENTS InGaAs/InAlAs/InP High Electron Mobility Transistor S-parameter measurements on extended (InP HEMT) devices that have achieved extrapolated reference plane 2 finger 20 um grounded CPW Fmax above 1 THz for the first time to the best of our devices with 2-mil thick substrates were measured knowledge and is validated by the demonstration of a from 1-110 GHz. The grounded CPW and extended 3-stage low noise MMIC amplifier at 340 GHz with reference plane serve to reduce measurement and greater than 15 dB gain. calibration issues such as probe coupling and substrate modes. The device performance is deInP HEMT DEVICE FABRICATION embedded using an EM simulated SOLT calibration To develop the THz Fmax InP HEMT device, structures fabricated on-wafer. H21 and maximum several process enhancements were implemented on stable gain (MSG) are relatively smooth and follows NGST's baseline InP HEMTs [4]. One key process the theoretical slope of -20 dB/decade and -10 enhancement was the reduction of gate length from dB/decade slope closely from 1 -110 GHz. The 70 to less than 50 nm. Based on cross sections ext...

Aims. This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods. The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480−1250 GHz with SIS mixers and the 1410−1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s −1 . Results. After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.

Abstract-We present an overview of solid-state integrated circuit amplifiers approaching terahertz frequencies based on the latest device technologies which have emerged in the past several years. Highlights include the best reported data from heterojunction bipolar transistor (HBT) circuits, high electron mobility transistor (HEMT) circuits, and metamorphic HEMT (mHEMT) amplifier circuits. We discuss packaging techniques for the various technologies in waveguide modules and describe the best reported noise figures measured in these technologies. A consequence of THz transistors, namely ultra-low-noise at cryogenic temperatures, will be explored and results presented. We also present a short review of power amplifier technologies for the THz regime. Finally, we discuss emerging materials for THz amplifiers into the next decade.

We report the detection of absorption lines by the reactive ions OH + , H 2 O + and H 3 O + along the line of sight to the submillimeter continuum source G10.6−0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH + at 971 GHz, H 2 O + at 1115 and 607 GHz, and H 3 O + at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6−0.4 as well as in the molecular gas directly associated with that source. The OH + spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H 2 O + lines remains lower than 1 in the same velocity range, and the H 3 O + line shows only weak absorption. For LSR velocities between 7 and 50 km s −1 we estimate total column densities of N(OH + ) ≥ 2.5 × 10 14 cm −2 , N(H 2 O + ) ∼6 × 10 13 cm −2 and N(H 3 O + ) ∼4.0 × 10 13 cm −2 . These detections confirm the role of O + and OH + in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH + by the H 2 O + column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.

We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH + and the 1115 GHz 1 11 −0 00 transition of ortho-H 2 O + . The resultant spectra show absorption by ortho-H 2 O + , and strong absorption by OH + , in foreground material at velocities in the range 0 to 70 km s −1 with respect to the local standard of rest. The inferred OH + /H 2 O + abundance ratio ranges from ∼3 to ∼15, implying that the observed OH + arises in clouds of small molecular fraction, in the 2−8% range. This conclusion is confirmed by the distribution of OH + and H 2 O + in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH + /H abundance ratio of a few ×10 −8 suggests a cosmic ray ionization rate for atomic hydrogen of 0.6−2.4 × 10 −16 s −1 , in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H + 3 and other species.

The InAs/Ga1−xInxSb strained-layer superlattice (SLS) holds promise as an alternative III–V semiconductor system for long wavelength infrared detectors. In this article, we present the first investigation, to the best of our knowledge, of heterojunction photodiodes using this new material. The devices were grown by molecular beam epitaxy on GaSb substrates, and are comprised of a 38 Å InAs/16 Å Ga0.64In0.36Sb SLS used in double heterojunctions with GaSb contact layers. The structures were designed to optimize the quantum efficiency while minimizing transport barriers at the heterointerfaces. The photodiodes are assessed through the correlation of their performance with the SLS material quality and the detector design. X-ray diffraction, absorption, and Hall measurements are used to determine the SLS material properties. The electrical and optical properties of the photodiodes are determined using current–voltage and spectral responsivity measurements. At 78 K, these devices exhibit rectifying electrical behavior and photoresponse out to a wavelength of 10.6 μm corresponding to the SLS energy gap. The responsivity and resistance in these thin-layered (0.75 μm), unpassivated photodiodes result in a detectivity of 1×1010 cm √Hz/W at 8.8 μm and 78 K. Based upon the performance of these devices, we conclude that high-sensitivity operation of long-wavelength photovoltaic detectors at temperatures well in excess of conventional III–V band gap-engineered systems, and potentially in excess of HgCdTe, is feasible using this material system.

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