A wireless communication system with a maximum data rate of 100 Gbit s−1 over 20 m is demonstrated using a carrier frequency of 237.5 GHz. The photonic schemes used to generate the signal carrier and local oscillator are described, as is the fast photodetector used as a mixer for data extraction.

Wireless sub-THz communication system with high data rate

Infrared (2–12 μm) solid-state laser sources: a review

The wavelength range around 2 μm which is covered by the laser systems described in this chapter is part of the so called “eye safe” wavelength region which begins at about 1.4 μm. Laser systems that operate in this region offer exceptional advantages for free space applications compared to conventional systems that operate at shorter wavelengths. This gives them a great market potential for the use in LIDAR and gas sensing systems and for direct optical communication applications. The favourable absorption in water makes such lasers also very useful for medical applications. As it can be seen in figure 1, there is a strong absorption peak near 2 μm which reduces the penetration depth of this wavelength in tissue to a few hundred μm.

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2 µm Laser Sources and Their Possible Applications

This paper critically investigates the advantages and limitations of the current-transient methods used for the study of the deep levels in GaN-based high-electron mobility transistors (HEMTs), by evaluating how the procedures adopted for measurement and data analysis can influence the results of the investigation. The article is divided in two parts within Part I. 1) We analyze how the choice of the measurement and analysis parameters (such as the voltage levels used to induce the trapping phenomena and monitor the current transients, the duration of the filling pulses, and the method used for the extrapolation of the time constants of the capture/emission processes) can influence the results of the drain current transient investigation and can provide information on the location of the trap levels responsible for current collapse. 2) We present a database of defects described in more than 60 papers on GaN technology, which can be used to extract information on the nature and origin of the trap levels responsible for current collapse in AlGaN/GaN HEMTs. Within Part II, we investigate how self-heating can modify the results of drain current transient measurements on the basis of combined experimental activity and device simulation.

Deep-Level Characterization in GaN HEMTs-Part I: Advantages and Limitations of Drain Current Transient Measurements

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.

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An Overview of Solid-State Integrated Circuit Amplifiers in the Submillimeter-Wave and THz Regime

The dependence of the beam quality of tapered laser oscillators and amplifiers on the modal optical gain is demonstrated experimentally and theoretically for the first time. Tapered devices with high- (HMG) and low-modal gain (LMG) structures are compared in terms of output power and beam quality. At high-output powers the beam quality of LMG devices is by a factor of ten better than the beam quality of high-modal gain devices. The beam quality remains nearly unchanged up to power levels of more than 2-W continuous-wave (CW) where a beam quality factor of M/sup 2/<3 is achieved for both, tapered laser oscillators and tapered amplifiers.

High-brightness tapered semiconductor laser oscillators and amplifiers with low-modal gain epilayer-structures

A metamorphic high electron mobility transistor (mHEMT) technology featuring 35 nm gate length has been developed. The optimized MBE grown layer sequence has a channel mobility and a channel electron density as high as 9800 cm2/Vs and 6.1times1012 cm-2, respectively. To enable a maximum extrinsic transconductance gm, max of 2500 mS/mm the source resistance has been reduced to 0.1 Omegamiddotmm. An ft of 515 GHz was achieved for a 2 times 10 mum device. Based on this advanced 35 nm mHEMT technology very compact single-stage H-band amplifiers circuits have been realized demonstrating a high small-signal gain of more than 7 dB at 270 GHz.

35 nm metamorphic HEMT MMIC technology

A metamorphic HEMT (MHEMT) MMIC technology including circuit applications is presented. The MHEMT layers are MBE grown on 4-inch GaAs wafers. The technology is based on a 50 nm gate length MHEMT and includes a 50 mum substrate backside process with dry etched through-substrate vias. For the electron confinement an ln0.8Ga0.2As/ln0.53Ga0.47As composite channel was used. The devices are passivated with BCB and SiN to achieve a median time-to-failure of 2.7 times 106 h in air. Cut-off frequencies ft and fmax of 375 GHz were extrapolated for a 2 times 15 mum gate width device. Low-noise amplifiers with more than 15 dB gain in the frequency range from 192 GHz to 235 GHz were realized.

50 nm MHEMT Technology for G- and H-Band MMICs

High-efficiency tapered diode lasers with ridge-waveguide structure emitting at 976 nm have been realised. High wall-plug efficiencies of more than 57% result in output powers of more than 12 W for a single emitter with 3.5 mm resonator length. A nearly diffraction limited behaviour has been demonstrated up to 8.3 W CW.

Michael Mikulla

Papers

Deep-Level Characterization in GaN HEMTs-Part I: Advantages and Limitations of Drain Current Transient Measurements

High-brightness tapered semiconductor laser oscillators and amplifiers with low-modal gain epilayer-structures

35 nm metamorphic HEMT MMIC technology

50 nm MHEMT Technology for G- and H-Band MMICs

Tapered diode lasers at 976 nm with 8 W nearly diffraction limited output power