High-speed InAlAs/InGaAs heterojunction bipolar transistors

InAlAs/InGaAs heterojunction bipolar transistors fabricated from wafers grown by molecular beam epitaxy are discussed. A cutoff frequency of 32 GHz for a collector current of 20 mA is achieved in the emitter area of devices 6×10 μm². The use of heavily doped and nondoped InGaAs layers as the emitter cap and collector, respectively, results in a reduction of the emitter and collector charging times; this, in turn, leads to improved microwave performance     

Simulation of PNP InAlAs/InGaAs heterojunction bipolar transistors

The performance of single heterojunction InAlAs/InGaAs PNP heterojunction bipolar transistors is modeled numerically and good agreement is found with experimental measurements. Peak experimental values of f_T=14 GHz, f_Max=22 GHz, β=170 and U=38 dB are obtained near a collector current density of 10⁴ A/cm² for a nonoptimized device     

InAlAs/InGaAs heterojunction bipolar transistors with AlAs etch-stop layer

A seven monolayer AlAs layer was used as an etch stop at the emitter-base heterojunction of an Npn In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As HBT. The etch-stop HBTs displayed higher DC gain and similar microwave performance when compared to devices without the AlAs layer.<>     

Low-frequency noise performance of self-aligned InAlAs/InGaAs heterojunction bipolar transistors

The first measurement of low-frequency noise performance for self-aligned InAlAs/InGaAs HBTs is reported. The 1/f noise obtained was around 20 dB lower than that for AlGaAs/GaAs HBTs at a fixed frequency, which is considered to be caused by the low surface recombination velocity of InGaAs.<>     

A collector current model for InAlAs/InGaAsSb/InGaAs double heterojunction bipolar transistors with non-ideal effects

A collector current model incorporating electron diffusion in the base and thermionic emission at the abrupt B–E heterojunction is derived and applied to InGaAsSb heterojunction bipolar transistors (HBTs). Parameters extracted from the model include effective base doping concentration, conduction band discontinuity (ΔE_C) at the base-emitter junction, and emitter resistance. The calculated current from the model is consistent with the measured result. It is found that a high collector current ideality factor is resulted from a nonzero ΔE_C and a low effective base doping concentration. Moreover, a nonzero ΔE_C makes the high-injection effect almost invisible in collector current characteristics, even if it actually exists.     

The effects of base dopant diffusion on DC and RF characteristicsof InGaAs/InAlAs heterojunction bipolar transistors

The effects of base p-dopant diffusion at junction interfaces of InGaAs/InAlAs HBTs with thin base thicknesses and high base dopings are reported. It is shown that HBTs with compositionally graded emitter-based (E-B) junctions are very tolerant to base dopant outdiffusion into the E-B graded region. The RF performance is nearly unaffected by the diffusion, and the DC current gain and E-B junction breakdown voltages are improved with finite Be diffusion into the E-B graded region     

Application of O+implantation in inverted InGaAs/InAlAs heterojunction bipolar transistors

Deep O+ implantation has been used to create a high-resistivity layer buried beneath the Be+ -implanted extrinsic base-emitter junction region of In0.52Al0.48As/In0.53Ga0.47As inverted (emitter-down) heterojunction bipolar transistors (HBT's). The O+ -implanted layer remains highly resistive even after a rapid thermal annealing step at 700°C to activate the Be+ implants. With the O+ implantation, the forward current of the extrinsic base-emitter diode is significantly reduced. HBT's with Be+ - and O+ -implanted extrinsic base regions exhibit current gains of ≃ 100 at a collector current density in excess of 10³A/cm². Another benefit from the deep O+ -implanted layer is a dramatic reduction in the junction capacitance of the extrinsic base-emitter diode.     

Ultra-high-speed InP/InGaAs heterojunction bipolar transistors

We report on the microwave performance of InP/In_0.53Ga _0.47As heterojunction bipolar transistors (HBT's) utilizing a carbon-doped base grown by chemical beam epitaxy (CBE). The f_T and f_max of the HBT having two 1.5×10 μm² emitter fingers were 175 GHz and 70 GHz, respectively, at I_C=40 mA and V_CE=1.5 V. To our knowledge, the f _T of this device is the highest of any type of bipolar transistors yet reported. These results indicate the great potential of carbon-doped base InP/InGaAs HBT's for high-speed applications     

High-speed InP/InGaAs heterojunction bipolar transistors

Very-high-performance common-emitter InP/InGaAs single heterojunction bipolar transistors (HBTs) grown by metalorganic molecular beam epitaxy (MOMBE) are reported. They exhibit a maximum oscillation frequency (f_T) of 180 GHz at a current density of 1×10⁵ A/cm². this corresponds to an (R_BC_BC)_eff=f _T/(8πf²_max) delay time of 0.12 ps, which is the smallest value every reported for common-emitter InP/InGaAs HBTs. The devices have 11 μm² total emitter area and exhibit current gain values up to 100 at zero base-collector bias voltage. The breakdown voltage of these devices is high with measured BV_CEO and BV_CEO of 8 and 17 V, respectively     

InP/InGaAs heterojunction bipolar transistors grown by gas-sourcemolecular beam epitaxy with carbon-doped base

The first N-p-n InP/InGaAs heterojunction bipolar transistors (HBTs) with p-type carbon doping in InGaAs are reported. P-type carbon doping in the InGaAs base has been achieved by gas-source molecular beam epitaxy (GSMBE) using carbon tetrachloride (CCl₄) as the dopant source. The resulting hole concentration in the base was 1×10¹⁹ cm^-3. HBTs fabricated using material from this growth method display good I-V characteristics with DC current gain above 500. This verifies the ability to use carbon doping to make a heavily p-type InGaAs base of an N-p-n HBT     

InGaAs/InP composite collector heterostructure bipolar transistors

A high speed bipolar transistor with high breakdown voltage BV/sub CEO/ is described. The structure uses a composite collector of InGaAs and InP. A common emitter gain of 65 is obtained with a base doping of 7*10/sup 19/ cm/sup -3/ and a breakdown voltage in excess of 10 V. The f/sub T/=64 GHz was reached at a collector-emitter voltage of 2 V and a current density of 52 kA/cm/sup 2/. The potential of this structure for very high speed applications is demonstrated by the extracted intrinsic transit time of 0.4 ps.<>     

High-gain InGaAlAs/InGaAs heterojunction bipolar transistors andphototransistors

The characteristics of InGaAlAs/InGaAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy are described. A current gain of 15600 at a current density of ~10⁴ A/cm² and an emitter-base heterojunction ideality factor of 1.02 were measured. Appropriately designed InGaAlAs/InGaAs HBTs, when operated as phototransistors, also had high gains. A current gain of 1000 for a collector current of only 10 μA was obtained for phototransistors. Such high gains are due to low recombination currents as a consequence of the good crystalline quality of the InGaAlAs bulk and InGaAlAs/InGaAs interface     

Influence of base thickness on collector breakdown in abruptAlInAs/InGaAs heterostructure bipolar transistors

The avalanche process in the collector of abrupt Al_0.48In_0.52As-In_0.53Ga_0.47 As heterostructure bipolar transistors (HBTs) is reported. It is reported that the collector multiplication constant decreases monotonically with increasing base thickness. When the base thickness is less than the mean-free path for energy relaxation in the base, the avalanche process in the collector is enhanced by high-energy injection from the emitter. On the other hand, no such dependence is observed for long-base transistors with equilibrium base transport. These effects are expected as the emitter injection energy of 0.48 eV is appreciable compared to the impact ionization threshold of 0.83 eV in the InGaAs collector     

Be diffusion in InGaAs/InP heterojunction bipolar transistors

Classic signatures of Be diffusion were observed in InAlAs/InGaAs HBT's after elevated temperature bias stress, i.e., a positive shift in the Gummel plot, higher collector ideality, and higher offset voltage. An activation energy of 1.57 eV was calculated. Lifetimes of 3.3×106 h and 37000 h were extrapolated for low and high power operation, respectively. In contrast, an InP/InGaAs HBT with a C doped base showed no signatures of C diffusion. The results show that Be diffusion is manageable at lower power. They also support the idea that C is more stable than Be in this material system     

High-performance InP/InGaAs heterojunction bipolar transistors with highly carbon-doped base grown by chemical beam epitaxy

InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistors (HBTs) using a highly carbon-doped base are reported. High carbon doping has been achieved by chemical beam epitaxy (CBE). The resulting hole concentration in the carbon-doped base is as high as 7*10/sup 19//cm/sup 3/. To the authors' knowledge, this is the highest doping level reported using carbon. HBTs with a 20 AA spacer layer exhibited nearly ideal I-V characteristics with collector and base current ideality factor of 1.018 and 1.037, respectively. Current gain and breakdown voltage BV/sub CEO/ were 7 and 6 V, respectively.<>     

Magnetotransport characterization of surface-treated InP/InGaAs heterojunction bipolar transistors

The results of surface modification induced effects on InP/InGaAs single heterojunction bipolar transistors, as revealed by magnetotransport experiments, are described here. The surface treatments included both sulphur-based surface passivation and ion bombardment-induced surface damage. The former is known to improve device characteristics and the latter to degrade device operation. In this work the aim was to assess these techniques for tailoring device performance for surface sensing applications. Device characteristics were found to be sensitive to surface preparation prior to measurements. Measurements revealed that surface treatments that improve device performance also reduce sensitivity to external magnetic fields while treatments that degrade performance make devices more sensitive to externally applied magnetic fields.     

InP/InGaAs heterojunction bipolar transistors with different g-bridge structures

Several μ-bridge structures for InP-based heterojunction bipolar transistors (HBTs) are reported. The radio frequency measurement results of these InP HBTs are compared with each other. The comparison shows that μ-bridge structures reduce the parasites and double μ-bridge structures have a better effect. Due to the utilization of the double μ-bridges, both the cutoff frequency f_T and also the maximum oscillation frequency f_(max) of the 2×12.5 μm~2 InP/InGaAs HBT reach nearly 160 GHz. The results also show that the μ-bridge has a better effect in increasing the high frequency performance of a narrow emitter InP HBT.     

Self-aligned InAlAs/InGaAs heterojunction bipolar transistor with aburied subcollector grown by selective epitaxy

We report the first microwave characterization of an In_0.52 Al_0.48As/In_0.53Ga_0.47As heterojunction bipolar transistor (HBT) with a buried InGaAs subcollector grown by selective epitaxy. The study compares two HBT's having identical 2×10 μm² self-aligned emitter fingers but different subcollectors. Improvement in microwave performance of the selectively-grown HBT over the conventional HBT was observed due to the reduced parasitic base-collector capacitance achieved by incorporating the selectively-grown buried subcollector     

AlGaAs/InGaAs/GaAs strained-layer heterojunction bipolar transistors by molecular beam epitaxy

The growth and characteristics of the first AlGaAs/InGaAs/GaAs HBTs are reported. Layers with up to 10% indium content appeared to be free of misfit dislocations, and resulted in HBTs with good I/V characteristics which scaled with In content according to theory.     

Predicted performance of high-speed integrated-injection logicusing InGaAs/InP heterojunction bipolar transistors

By the use of analytical expressions and SPICE simulation, the switching performance of integrated injection logic (I²L) using heterojunction bipolar transistors (HBTs) has been investigated. A proposed inverter configuration using InP/InGaAs HBTs which avoids saturation in the p-n-p injector has predicted propagation delays of 16 ps at only 3-mW power dissipation. Transient response analysis illustrates the importance of reducing parasitic resistances in the structure. Ring oscillator simulations indicate that switching speeds approaching those of emitter-coupled logic but with advantages in high density and low power are possible