M. Asaka

LPMOCVD growth of C doped GaAs layers and AlGaAs/GaAs heterojunction bipolar transistors

Low-pressure MOCVD growth of GaAs using trimethylgallium (TMG) and arsine was investigated under conditions of low growth temperatures and low V/III ratios. The growth rate was limited not by the supply rate of TMG but by surface kinetics. Incorporation of carbon atoms was enhanced by decreasing the growth temperature and V/III ratio. GaAs layers with hole concentrations as high as 6×1019 cm-3 were obtained with a V/III ratio near unity. AlGaAs/GaAs heterojunction bipolar transistors with carbon doped GaAs bases were fabricated using this novel growth technique. The diffusion of carbon atoms was so small that a spacer layer, in the base, as narrow as 10Awas found to be sufficiently effective to establish the emitter-base junction.

Transit-time reduction in AlGaAs/GaAs HBTs utilizing velocity overshoot in the p-type collector region

The effect of electron-velocity overshoot in a p-type GaAs collector on the transit-time reduction of AlGaAs/GaAs HBTs (heterojunction bipolar transistors) is investigated. A cutoff frequency improvement of about 30% over the conventional n-type GaAs collector was obtained in p-type collector HBTs for the same collector depletion-layer width. A significant increase in electron velocity in the p-type GaAs collector layer was confirmed by a simple analysis.<<ETX>>

AlGaAs/GaAs HBTs fabricated by a self-alignment technology using polyimide for electrode separation

A self-aligned HBT (heterojunction bipolar transistor) technology using polymide for insulating the emitter contact from the base contact is described. A 1- mu m emitter-width HBT with maximum oscillation frequency of 86 GHz was successfully fabricated. This processing was also applied to fabricate frequency-divider ICs. An operating frequency of 18 GHz was obtained with good reproducibility.<<ETX>>

AlGaAs/GaAs HBT receiver ICs for a 10 Gbps optical communication system

Key component ICs for an optical communication system such as an equalizing amplifier a rectifier, and a limiting amplifier were fabricated with AlGaAs/GaAs HBTs. The equalizing amplifier with an amplitude detection circuit had an 11 GHz bandwidth, 30-dB maximum voltage gain and over 30-dB controllable gain width. The rectifier could extract 10-GHz signals, and the limiting amplifier had a 36-dB voltage gain at 10 GHz and an over 20-dB dynamic range with an under 10 degrees phase-shift deviation. These optical receiver ICs have a performance sufficient for 10-Gbit/s optical communication system.<<ETX>>

Electron space-charge effects on high-frequency performance of AlGaAs/GaAs HBTs under high-current-density operation

The high-frequency characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) under high-current-density biasing condition are investigated in conjunction with the electron space charge in the collector depletion layer. A significant increase in cutoff frequency f/sub t/ and maximum oscillation frequency f/sub max/ at the early stage of the base push-out was observed in HBTs with a lightly doped n-type collector structure, and is attributed to the collector depletion layer widening and the enhancement of the velocity overshoot effect caused by the increasing electron density.<<ETX>>

Ultra-low resistance base ohmic contact with Pt/Ti/Pt/Au for high-fmax AlGaAs/GaAs heterojunction bipolar transistors

Ohmic contacts to 500-A-thick p-Al0.1Ga0.9As layer formed with a Pt/Ti/Pt/Au metal system were investigated. An extremely low contact resistivity of 4.2×10-7 Ω cm2 was obtained. The contact resistance increased with the increment of the Pt thickness, because the thicker the intermetallic layer becomes the thinner the AlGaAs layer beneath it, which leads to a higher contact resistance. The optimum Pt thickness was around 50 A. Moreover, this metal scheme was thermally stable at 350° C. A high f max of 160 GHz was obtained for AlGaAs/GaAs HBTs using Pt/Ti/Pt/Au base electrodes. A multiplexer (MUX) lC implemented with these high-f max HBTs operated properly up to 40 Gbps, the highest speed ever reported. This value was restricted by the measuring instrument capability.

15 GBPS MUX/DMUX implemented with AlGaAs/GaAs HBTs

AlGaAs/GaAs HBTs (heterojunction bipolar transistors) with improved high-speed performance obtained by a self-alignment technology and a new layer design have been used to construct ultra-high-speed MUX (multiplexer) and DMUX (demultiplexer) ICs. Quantitative error-free operation of these ICs was confirmed up to 10 Gb/s. Although only a few test patterns were available, the maximum operation speeds of the MUX and the DMUX were found to be around 15 Gb/s and 19 Gb/s, respectively. These results demonstrate the promising potential of HBTs for coming ultra-high-speed digital systems.<<ETX>>

Five AlGaAs/GaAs HBT ICs for a 20 Gb/s optical repeater

The development of future ultra high bit rate optical transmission systems is now under way to meet the need for a rapid increase in transmission capacity. The capability of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is already demonstrated by a 10 Gb/s optical transmission unit This paper describes a complete 5-chip set of AlGaAs/GaAs HBT ICs for a 20Gb/s direct detection optical repeater.<<ETX>>

Ultrahigh-speed heterojunction bipolar transistor multiplexer/demultiplexer ICs

High-speed 2-b monolithic integrated multiplexer (MUX) and demultiplexer (DMUX) circuits have been developed using self-aligned AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with improved high-speed performance. Both ICs were designed using emitter-coupled logic. The 2:1 MUX was composed of a D-type flip-flop (D-FF) merging a selector gate and a T-type flip-flop (T-FF). The 1:2 DMUX consisted of two D-FFs driven at a clock of half the rate of the input data. Error-free operation with a pseudorandom pattern was confirmed up to 10 Gb/s. The rise and fall times of the output signals of both ICs were 40 and 25 ps, respectively. HBT frequency dividers were used as inputs for both ICs in order to find the maximum operation speed. Although only a few test patterns were available, the maximum operation speeds of the MUX and DMUX were found to be around 15 and 19 Gb/s, respectively. >

Reliability characteristics of mesa-etched isolated emitter structure AlGaAs/GaAs HBTs with Be-doped base

High-temperature bias stress tests were carried out on AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with a 5*10/sup 19/ cm/sup -3/ Be-doped base. It was shown that HBTs with a mesa-etched isolated emitter structure were more durable than ion-implanted isolated emitter structure HBTs in terms of switch-on voltage stability. This result implies that the base/emitter junction edge, which makes contact with the ion-implanted defect-rich region, plays an important role in reliability characteristics. The lifetime of mesa-etched isolated emitter structure HBTs was also considered. It was found that the lifetime was determined by a reduction in hfe. The mean time to failure was estimated at 9.6*10/sup 5/ hours at 25 degrees C.<<ETX>>