This paper investigates current-gain and high-frequency characteristics of double heterojunction bipolar transistors (DHBTs) with a uniform GaAsSb, compositionally graded GaAsSb, uniform InGaAsSb, or compositionally graded InGaAsSb base. DHBTs with a compositionally graded InGaAsSb base exhibit a high current gain of ∼75 and fT=504GHz. In order to boost fmax of DHBTs with a compositionally graded InGaAsSb base, a highly doped GaAsSb base contact layer is inserted. The fabricated DHBTs exhibit fT/fmax=513/637GHz and a breakdown voltage of 5.2V.

We propose a novel structure that can reduce the power consumption and extend the transmission distance of an electro-absorption modulator integrated with a DFB (EADFB) laser. To overcome the trade-off relationship of the optical loss and chirp parameter of the EA modulator, we integrate a semiconductor optical amplifier (SOA) with an EADFB laser. With the proposed SOA assisted extended reach EADFB laser (AXEL) structure, the LD and SOA sections are operated by an electrically connected input port. We describe a design for AXEL that optimizes the LD and SOA length ratio when their total operation current is 80mA. By using the designed AXEL, the power consumption of a 10-Gbit/s, 1.55-µm EADFB laser is reduced by 1/2 and at the same time the transmission distance is extended from 80 to 100km.

An active integrated antenna (AIA) oscillator consisting of an active circuit and planar antenna on the same substrate can be used as a high-performance, low-cost, small component for millimeter-to-sub-millimeter wave applications. We describe a highly extended, finite-difference-time-domain full-wave analysis method for designing AIA circuits precisely. It treats active devices as distributed elements. Using this method and 0.1-µm-gate InP-based HEMTs, we fabricated W-band AIA oscillators with an oscillation frequency of 111 GHz.

An SCFL-compatible 40-Gbit/s selector circuit using resonant tunneling diodes (RTDs) and high-electron-mobility transistors (HEMTs) is presented. The circuit comprises two monostable-bistable transition elements (MOBILEs) using RTDs, a HEMT NOR circuit, and a HEMT output buffer based on source-coupled-FET logic (SCFL). The circuit is fabricated by monolithically integrating RTDs and 0.1-µm HEMTs on an InP substrate. The fabricated circuit exhibits clear eye-opening at 40 Gbit/s with an output swing of 800 mVp-p, which is close to the conventional high-speed logic IC interface called SCFL.

A novel fabrication technology for lateral scale-down of sub-100-nm-gate InP-based HEMTs is presented. The fabricated device, whose structure features a reduced distance between the gate and ohmic metals of less than 100 nm, exhibits low ohmic resistances and improved DC and RF characteristics with good uniformity across a wafer. A fabricated 130-nm-gate lattice-matched InAlAs/InGaAs HEMT exhibits an extrinsic transconductance of 1.3 S/mm. This is 25% increase compared to that of a HEMT fabricated with our conventional process, which is explained by the reduction of RS. The average current-gain-cutoff-frequency (fT) of 261 GHz was obtained with a small deviation of 9.0 GHz. Uniform characteristics with high yield were also confirmed for HEMTs with shorter gates. The average fT of 290 GHz with a standard deviation of 9.3 GHz was obtained for 55-nm-gate HEMTs. The developed fabrication technology is promising for improving the electrical characteristics of sub-100-nm-gate InP-based HEMTs and for their integration.