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Quantum-well lasers that exploit tunneling for electron injection into the quantum well ground state exhibit negligible gain compression, superior high-temperature performance, lower Auger recombination and improved modulation characteristics. Lasers of the type InGaAs-GaAs-AlGaAs show both single and multiple quantum-well tunneling injection phenomena. The physical principles behind the superior performance are explored, and relaxation time measurements in quantum wells are presented.

The spectral response characteristics and carrier impact ionization coefficients of Si(sub 1 - x)Ge(sub x) photodiodes grown by MBE are determined. The ratio of electron and hole impact ionization coefficients is computed and is shown to agree well with published data from Si and Ge. The ratio attains unity at x = 0.45 representing a cross-over in the alloy system. Detailed measurement results having important photodetection applications are presented.

This paper reports on a dc-20-GHz InP heterojunction bipolar transistor (HBT) active mixer, which obtains the highest gain-bandwidth product (GBP) thus far reported for a direct-coupled analog mixer integrated circuit (IC). The InP HBT active mixer is based on the Gilbert transconductance multiplier cell and integrates RF, local oscillator, and IF amplifiers. High-speed 70-GHz [f.sub.T] and 160-GHz [f.sub.max] InP HBT devices along with microwave matching accounts for its record performance. Operated as a down-converter mixer, the monolithic microwave integrated circuit achieves an RF bandwidth (BW) from dc-20 GHz with 15.3-dB gain and benchmarks a factor of two improvement in GBP over state-of-the-art analog mixer IC's [1]-[9]. Operated as an up-converter, direct-digital modulation of a 2.4-Gb/s [2.sup.31] - 1 pseudorandom bit sequence (PRBS) onto a 20-GHz carrier frequency resulted in a carrier rejection of a 28 dB, clock suppression of 45 dBc, and less than a 50-ps demodulated eye phase jitter. The analog multiplier was also operated as a variable gain amplifier, which obtained 20-dB gain with a BW from dc-18 GHz, an third-order intercept of 12 dBm, and over 25 dB of dynamic range. A single-ended peak-to-peak output voltage of 600 mV was obtained with a [+ or -] 35-mV 15 Gb/s [2.sup.5] - 1 PRBS input demonstrating feasibility for OC-192 fiber-telecommunication data rates. The InP-based analog multiplier IC is an attractive building block for several wide-band communications such as those employed in satellites, local multipoint distribution systems, high-speed local area networks, and fiber-optic links. Index Terms--Fiber optics, InP HBT, limiter, mixer, multiplier, VGA.