Subpicosecond InP/InGaAs heterostructure bipolar transistors

Bipolar transistors with subpicosecond extrinsic delay are discussed. These InP/InGaAs heterostructure transistors show a unity-current-gain cutoff frequency f_$T=165 GHz and maximum oscillation frequency f_MAX=100 GHz at room temperature. The authors model shows that an f_$T beyond 386 GHz is obtainable by further vertical scaling. Ring oscillators implemented with nonthreshold logic (NTL) and transistors having f_MAX=71 GHz show a propagation delay of 14.7 ps and 5.4 mW average power consumption per stage     

Selfaligned InGaAs/InP heterostructure bipolar transistors

InGaAs/InP heterostructure bipolar transistors have been realised using a new selfaligned process. Transistor wafers were grown by chemical beam epitaxy. Ideality factors close to unity were measured for emitter-base and collector-base diodes. The resulting devices exhibit nearly constant gain over four orders of magnitude of collector current densities, from j=1.5*10/sup -4/ A/cm/sup 2/ to 1.5 A/cm/sup 2/.<>     

InP/InGaAs double heterostructure bipolar transistors grown by MBE

Double heterostructure bipolar transistors have been fabricated on InP/InGaAs MBE material. Current gains of up to 80 have been observed in the emitter-up configuration. The devices were fabricated using two diffusion techniques and selective etching to contact the base.     

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     

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     

InP/InGaAs double-heterojunction bipolar transistors for high-speedoptical receivers

We fabricated monolithically integrated pin/HBT photoreceivers using FPIGA (full-potential InGaAs) DHBT's with various collector thicknesses. An HBT figure-of-merit was deduced from the relationship between measured bandwidths of the preamplifiers and the f_T's and f_max's of the DHBT's. A phenomenological device model of the DHBT's is proposed to find the optimum collector thickness that gives the highest bandwidth of the photoreceivers. Finally, we discuss the feasibility of monolithically integrating a pin-PD, preamplifier, buffer amplifier, and D-type flip-flop with an operating speed of 40 Gbit/s     

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     

DC and temperature dependent characteristics of InP double heterostructure bipolar transistors with quaternary collector

Reports the first study of the temperature dependence of the DC characteristics of InP-based double heterostructure bipolar transistors which have a quaternary collector. The quaternary layer was spaced away from the base-collector junction to improve the HBT characteristics. The devices exhibited useful gain over seven orders of magnitude of current and had breakdown voltages of approximately 8 V. The DC gain decreased with decreasing temperature whereas the ideality factors increased.<>     

InP/InGaAs double-heterojunction bipolar transistor with step-graded InGaAsP collector

An MOCVD-grown InP/InGaAs double-heterojunction bipolar transistor with a step-graded InGaAsP collector is described. This transistor allows high injection current densities over 2.9*10/sup 5/ A/cm/sup 2/, which suggests no significant current blocking related to the wide-gap InP layers. A cutoff frequency of 155 GHz and a maximum oscillation frequency of 90 GHz are obtained at the collector current density of 1.6*10/sup 5/ A/cm/sup 2/.<>     

Breakdown-speed considerations in InP/InGaAs single- anddouble-heterostructure bipolar transistors

The breakdown and speed characteristics of InP/InGaAs single and double HBTs are presented. Temperature-dependent two- and three-terminal measurements suggest that avalanche impact ionization is the dominant breakdown mechanism in InGaAs collector HBTs. Monte Carlo techniques and 1D drift-diffusion modeling are used for speed and breakdown simulation, respectively. Special doping profiles are evaluated for improving the breakdown-speed characteristics of single HBTs (SHBTs) with conventional uniformly doped InGaAs collectors. Double HBTs (DHBTs) outperform all SHBTs in terms of speed-breakdown tradeoffs as long as they use graded base-collector junctions or they operate under sufficiently high collector-emitter voltage conditions. A cutoff frequency of 200 GHz was found to be feasible with graded DHBTs, and breakdown voltages up to 4.6 V were evaluated with a 3000-Å-thick collector. Nongraded DHBTs can be optimized to perform better in terms of speed-breakdown tradeoffs provided that a high collector doping is used     

On the storage time of InGaAs/InP bipolar transistors

The collector storage time was measured for InGaAs/InP bipolar transistors. For the evaluation, the transistors were driven into deep saturation choosing a test condition with no reverse base current. Devices comprising a homojunction- and a modified wide-gap-collector structure, respectively, were compared. For the latter device structure a marked reduction of the storage time by a factor of 10 was found.     

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.     

Hot-electron InGaAs/InP heterostructure bipolar transistors withfT of 110 GHz

A hot-electron InGaAs/InP heterostructure bipolar transistor (HBT) is discussed. A unity-current-gain cutoff frequency of 110 GHz and a maximum frequency of oscillation of 58 GHz are realized in transistors with 3.2×3.2-μm² emitter size. Nonequilibrium electron transport, with an average electron velocity approaching 4×10⁷ cm/s through the thin (650 Å) heavily doped (p=5×10¹⁹ cm^-3) InGaAs base and 3000-Å-wide collector space-charge region, results in a transit delay of 0.5 ps corresponding to an intrinsic cutoff frequency of 318 GHz     

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.     

High-speed InGaAs(P)/InP double-heterostructure bipolar transistors

Double-heterostructure InGaAs(P)/InP bipolar transistors ranging in emitter size from 5 × 10 to 100 × 150 µm²have been fabricated using a non-self-aligned technology. These transistors exhibit current gains as high as 275 independent of emitter perimeter-to-area ratio. The best frequency of unity current gain was measured in the smallest devices to be 18 GHz. The high-frequency operation was mainly limited by the emitter charging time.     

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     

Comparative investigation of InP/InGaAs heterostructure-emitter tunneling and superlattice bipolar transistors

In this article, the characteristics of InP/InGaAs heterostructure-emitter bipolar transistors with 30 n-InP layer tunneling layers and a five-period InP/InGaAs superlattice are demonstrated and comparatively investigated by experimentally results and analysis. In the three devices, a 200 Å n-In_0.53Ga_0.47As layer together with an n-InP tunneling emitter layer (or n-InP/n-InGaAs superlattice) forms heterostructure emitter to decrease collector-emitter offset voltage. The results exhibits that the largest collector current and current gain are obtained for the tunneling transistor with a 30 Å n-InP tunneling emitter layer. On the other hand, some of holes injecting from base to emitter will be blocked at n-InP/n-InGaAs heterojunction due to the relatively small hole transmission coefficient in superlattice device, which will result in a considerable base recombination current in the n-InGaAs layer. Therefore, the collector current and current gain of the superlattice device are the smallest values among of the devices.     

Millimetre-wave InP/InGaAs heterojunction bipolar transistors witha subpicosecond extrinsic delay time

We report the microwave characteristics of InP/InGaAs heterojunction bipolar transistors (HBTs) using a carbon-doped base grown by chemical beam epitaxy (CBE). An extrinsic delay time of 0.856 ps was achieved by nonequilibrium transport in a very thin base layer and extremely small emitter parasitic resistance through the use of silicon δ-doping in the emitter ohmic contact layer. To our knowledge, this is the shortest extrinsic delay time of any bipolar transistors reported. This result indicates the great potential of InP/InGaAs HBTs for applications requiring a very large bandwidth     

Low-base-resistance InP/InGaAs heterojunction bipolar transistors with a compositionally graded-base structure

To reduce base resistance of an InP/InGaAs heterojunction bipolar transistor grown by gas-source molecular beam epitaxy, the doping characteristics of carbon-doped InGaAs and the dependence of doping concentration on current gain were investigated. Using a thicker graded base was found to increase current gain significantly, resulting in increased doping level in the InGaAs: C-base layer. In particular, an 80-nm-thick graded base produces a base sheet resistance of 285 Ω/sq and maintains a practically useful current gain of 23 and a high cut-off frequency of 139 GHz.