This paper discusses crystal-growth and device-design issues associated with the development of high-performance InP/InGaAs heretostructure bipolar transistors (HBTs). It is shown that a highly Si-doped n+-subcollector in the HBT structure causes anomalous Zn redistribution during metalorganic vapor phase epitaxial (MOVPE) growth. A thermodynamical model of and a useful solution to this big problem are presented. A novel hybrid structure consisting of an abrupt emitter-base heterojunction and a compositionally-graded base is shown to enhance nonequilibrium base transport and thereby increase current gain and cutoff frequency fT. A double-heterostructure bipolar transistor (DHBT) with a step-graded InGaAsP collector can improve collector breakdown behavior without any speed penalty. We also elucidate the effect of emitter size shrinkage on high-frequency performance. Maximum oscillation frequency fmax in excess of 250 GHz is reported.

A wideband, low-power preamplifier and a high-speed, low-power monolithically integrated regenerative receiver are designed and fabricated using small-scale InP/InGaAs DHBTs. The preamplifier has a gain-bandwidth product of 192 GHz with a power dissipation of 51 mW. The regenerative receiver is successfully operated at 20 Gbit/s with a power dissipation of 0.6 W and an input dynamic range of 13 dB. This IC offers the lowest energy ever reported for regenerative receivers. In addition, a 20-Gbit/s optical modulator driver with a driving voltage of 2 V is successfully fabricated. These results demonstrate the feasibility of InP/InGaAs DHBTs for high-speed, low-power lightwave communication ICs.

This paper discusses direct optical injection locking of a millimeter-wave oscillator using an InP/InGaAs heterojunction phototransistor (HPT) and its applications. Previously reported optically injection-locked oscillators (OILOs) are reviewed first. In particular, the features of a direct OILO (DOILO), where synchronization can be achieved by illuminating the active oscillator device itself, are discussed in comparison with the indirect OILO. DOILOs with excellent characteristics require high-performance transistors having both a high maximum oscillation frequency and fast photoresponse. We have developed high-performance opto-microwave-compatible InP/InGaAs HPTs whose layer and fabrication process are fully compatible with ultrahigh-speed heterojunction bipolar transistors. The paper discusses the photocoupling structure, and it is shown that the back-illuminated structure with the aid of InP subcollector enables one to achieve a 100-GHz-class DOILO. The configuration and performance of the 100-GHz-class DOILO are then presented; in particular, injection locking from optical signals with a modulation or beat frequency of around the fundamental (96 GHz) or second harmonic (192 GHz) is successfully demonstrated. To our knowledge, 96 GHz is the highest optically injection-locked frequency and 192 GHz is the highest inputmodulation frequency reported for OILOs. The HPT oscillator IC promises compact, low-power-consumption remote local oscillators for 100-GHz-class wireless systems and 100-Gbit/s-class optoelectronic clock recovery circuits. In addition, when the HPT oscillator is used as a modulator, we can attain cost-effective millimeter-wave systems compatible with conventional optical fiber networks transmitting digitally modulated baseband signals.

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.

A design scheme for a high-speed differential-input limiting transimpedance amplifier (TIA) was developed. The output-stage amplifier of the TIA is investigated in detail in order to suppress undershoot and ringing in the output waveform. The amplifier also includes a peak detector for the received signal strength indicator (RSSI) output, which is used to control the optical demodulator for differential-phase-shift-keying or differential-quadrature-phase-shift-keying formats. The limiting TIA was fabricated on the basis of 1-µm emitter-width InP-based heterojunction-bipolar-transistor (HBT) IC technology. Its differential gain is 39 dB, its 3-dB bandwidth is 27 GHz, and its estimated differential transimpedance gain is 73 dBΩ. The obtained output waveform shows that the developed design scheme is effective for suppressing undershoot and ringing.

An electron-wave device consisting of a hot electron transistor structure with a transversal potential grating in a base region is proposed. A reduced transit time and extremely small charging times provide significant potential for high-speed operation.

A 3-bit flash analog-to-digital converter (ADC) for electronic dispersion compensation (EDC) was developed using InP HBTs. Nyquist operation was confirmed up to 24 Gsps, which enables oversampling acquisition for 10 Gbit/s non-return-to-zero (NRZ) signals. The ADC can also be operated at up to 37 Gsps for low input frequencies. To reduce aperture jitter and achieve a wide band of over 7 GHz, an analog input signal for all pre-amplifiers and a clock signal for all latched comparators are provided as traveling waves through coplanar transmission lines. EDC was demonstrated by capturing a 10-Gbit/s pseudo-random bit stream (PRBS) with the waveform degraded by polarization-mode dispersion (PMD). By using the captured data, we confirmed that a calculation of a transversal filter mitigates PMD.

Self-aligned InP/InGaAs heterojunction bipolar transistors (HBTs) were fabricated with emitter electrodes of 12, 22, 25, and 220 µm2 on the same wafer to investigate the influence of lateral scaling on device performance. DC characterization of these devices showed that InP/InGaAs HBTs are less subject to the emitter-size effect than GaAs-based HBTs. Common-emitter current gain β of the smallest 12-µm2 transistor was approximately 60 which is high enough for practical use. High-frequency characteristics of the transistors were almost the same in spite of the large difference in device size. Unity current-gain cutoff frequency fT of the smallest 12-µm2 transistor was as high as 163 GHz at a collector current of 2.3 mA, which ranks with the fT176 GHz achieved by the largest 220-µm2 transistor at a collector current of 45 mA. The smallest device also showed an excellent high-speed performance of fT100 GHz at submilliampere collector currents of Ic0.6 mA. The results indicate that small-lateral-dimension InP/InGaAs HBTs are applicable to high-speed ICs with low power dissipation.

This letter describes theoretical characteristics of the electron diffraction transistor and its inverter circuit. The electron wave diffraction due to a transverse potential grating is analyzed taking thermally induced dispersions into account. The switching time is estimated as 0.4 ps at 77 K.

We describe 150-nm-thick collector InP-based double heterojunction bipolar transistors with two types of thin pseudomorphic bases. The emitter and collector layers are designed for high collector current operation. The collector current blocking is suppressed by the compositionally step-graded collector structure even at JC of over 500 kA/cm2 with practical breakdown characteristics. An HBT with a 20-nm-thick base achieves a high fT of 351 GHz at high JC of 667 kA/cm2, and a 30-nm-base HBT achieves a high value of 329 GHz for both fT and fmax at JC of 583 kA/cm2. An equivalent circuit analysis suggests that the extremely small carrier-transit-delay contributes to the ultrahigh fT.

We have developed 0.5-µm-emitter InP-based HBTs with high reliability. The HBTs incorporate a passivation ledge structure and tungsten-based emitter metal. A fabricated HBT exhibits high collector current density and a current gain of 58 at a collector current density of 4 mA/µm2. The results of dc measurements indicate that the ledge layer sufficiently suppresses the recombination current at the emitter-base periphery. The HBT also exhibits an ft of 321 GHz and an fmax of 301 GHz at a collector current density of 4 mA/µm2. The ft does not degrade even though the emitter size is reduced to as small as 0.5 µm2 µm. The results of an accelerated life test show that the degradation of dc current gain is due to thermal degradation of the interfacial quality of semiconductors at the passivation ledge. The activation energy is expected to be around 1.5 eV, and the extrapolated mean time to failure is expected to be over 108 hours at a junction temperature of 125. These results indicate that this InP HBT technology is promising for making over-100-Gbit/s ICs with high reliability.

This paper investigates the effects of n-type doping in the emitter-base heterojunction vicinity on the DC and high-frequency characteristics of InP/InGaAs heterojunction bipolar transistors (HBTs). The n-type doping is shown to be very effective for enhancing the tunneling-injection current from the emitter and thus for reducing the collector-current turn-on voltage. However, it is also revealed that an unnecessary increase in the doping level only degrades the current gain, especially in the low-current region. A higher doping level also increases the emitter junction capacitance. The optimized HBT structures with a 0.5-µm-wide emitter exhibit turn-on voltage as low as 0.78 V and current gain of around 80 at JC = 1 mA/µm2. They also provide a current-gain cutoff frequency, ft, of 280 GHz and a maximum oscillation frequency, fmax, of 385 GHz at VCE = 1 V and JC = 3 mA/µm2. These results indicate that the proposed HBTs are very useful for high-speed and low-power IC applications.