Double Heterostructure Bipolar Transistors Research Articles

Electrical stress damage reversal in non-passivatedfully self-aligned InP HBTs by ozone surface treatment

The authors report that the degradation of device characteristics due to electrical stressing in non-passivated fully self-aligned InP-based heterostructure bipolar transistors (HBTs) can be reversed by a simple surface treatment in ozone. The technique is demonstrated on MOCVD-grown InP/GaAs0.51Sb0.49/InP double heterostructure bipolar transistors (DHBTs) with a C-doped base, and on conventional MBE-grown InP/Ga0.47In0.53As single heterostructure bipolar transistors (SHBTs) with a Be-doped base. This is the first report of the reversibility of bias stress damage in the extrinsic region of III-V HBTs: the experiments presented confirm that stress damage occurs at the exposed emitter periphery, thus explaining the success of emitter ledge passivation techniques.

Ultrahigh-Speed InP/InGaAs Double-Heterostructure Bipolar Transistors and Analyses of Their Operation

Novel hexagonal emitters are proposed for heterostructure bipolar transistors (HBTs) with a base-metal-overlaid emitter-base self-alignment structure to reduce parasitic effects. Two different layer structures for InP/InGaAs double-heterostructure bipolar transistors (DHBTs) that can more fully utilize the inherent potential of the materials are used to enhance unity current gain cutoff frequency, f T, and maximum oscillation frequency, fmax . On a wafer with a 180-nm-thick collector, a transistor with a 20-µ m2 hexagonal emitter electrode shows an f T of 230 GHz and an fmax of 147 GHz, while with a 4-µ m2 hexagonal emitter electrode the corresponding values are 225 GHz and 241 GHz. fmax of 300 GHz is achieved for a transistor with a 4-µ m2 emitter electrode and a 330-nm-thick collector. Transistor operation is analyzed using a simple but appropriate small-signal equivalent circuit model of a transistor that includes internal and external base/collector capacitances and yields good estimates of the measured scattering (s-) parameters. Even in these InP-based (D)HBTs, the internal collector capacitance increases with collector current density due to the Kirk effect which degrades performance. In thin-collector (D)HBTs, the increase in the internal collector capacitance is suppressed, which increases the collector current density at which the transistor can operate normally, and f T is increased by both transit time reduction and high-collector-current operation.

High-efficiency InP-based DHBT active frequency multipliers for wireless communications

We present, for the first time, the performance of AlInAs/GaInAs/InP double heterostructure bipolar transistors (DHBT's) as active frequency multipliers at frequencies of relevance to Wireless Communications applications. In particular, we present results comparing the performance of X6 (127/spl rarr/762 MHz) and X4 (762.5/spl rarr/3050.0 MHz) InP- and Si-based (NEC2107) multiplier circuits. A well-known multiplier circuit topology has been chosen as a vehicle, so that we can focus on active device comparison. The X6 InP-based multiplier exhibits output power and efficiency of +6 dBm and 11%, respectively, compared to +7.2 dBm and 4.8% of the Si-based circuit. The X4 InP-based multiplier exhibits output power and efficiency of +3.74 dBm and 8%, respectively, compared to -6.1 dBm and 0.4% of the Si-based circuit. The superior electronic properties of InP-DHBT's enable high-conversion gain/highly DC-efficient multipliers, however, their nonexponential I/sub C/-V/sub BE/ characteristic limits the maximum obtainable conversion gain at high-order frequency multiplication.

Current blocking in InP/InGaAs double heterostructure bipolar transistors

The one-flux analysis of double-heterostructure bipolar transistors with composite collectors in the preceding article W. R. McKinnon, J. Appl. Phys. 79, 2762 (1996) is compared to drift-diffusion calculations and to measurements on InP/InGaAs/InP/composite collectors-double heterostructure bipolar transistors. For quantitative agreement we include the effects of ionized impurities in the space-charge regions, and an approximate treatment of Fermi–Dirac statistics.

An analytical expression for base transit time in an exponentially doped base bipolar transistor

An analytical expression of base transit time for exponentially doped base, which is applicable to both homojunction and heterojunction bipolar transistors, is developed. The present treatment includes dopant dependent mobility variation, bandgap narrowing and finite velocity saturation effects in the calculation of base transit time and thus is a generalization of the results reported recently by Rosenfield and Alterovitz[6]. These effects degrade base transit time significantly and must be incorporated in the calculation. the finite velocity saturation effect will progressively play a pivotal role as the base width is scaled down and for double heterostructure bipolar transistor. The transition of base transit time from the ballistic and the drift-diffusion limit will occur at a longer base width if the base is exponentially doped with a sufficiently high doping index.

Oscillations in collector current of a double heterostructure bipolar transistor: a quantum effect

In spite of many advantages, GaInP/GaAs/GaInP double heterostructure bipolar transistors (DHBT) suffer from the disadvantage of energy barrier to flow of carriers at the collector-base junction due to non-zero conduction band edge discontinuity which results in higher V D,sat . To circumvent this critical problem, Liu et al. IEEE Transactions on Electron Devices, 40 , 1384-1389 (1993) have employed a set-back layer of undoped GaAs between the base and the collector. As a consequence of the set-back layer, they observed oscillations in the collector current in the forward active mode with the output voltage ( V BC ), the origin of which they proposed to be the presence and absence of resonant energy levels at the energy equal to the conduction band edge, E c , of the base. In this work, we have investigated the origin and conditions of these oscillations theoretically. Energy band balance was performed at the base-set-back layer and set-back layer-collector junctions to determine the distribution of the output voltage, V BC , at these junctions using degenerate statistics. This calculation also provided the electric field and potential drop on the set-back layer. The parabolic E c profiles of the base and collector depletion layers were linearized. The transmission coefficient as a function of energy was obtained using Airy and exponential function solutions to Schrödinger equation. The transmission coefficient was energy averaged for various V BC S and thus, a transmission parameter for the collector-base junction was obtained and used in a DC I-V characteristics model. Theoretical results are in excellent agreement with the experimental results with the V BC S at which the peaks of the collector current occurs matching closely for the first two peaks.

Formula omitted] double-heterostructure bipolar transistors for high-speed ICs and OEICs

This paper describes a novel collector structure for full-potential InGaAs (FPIGA) double-heterostructure bipolar transistors (DHBTs). This new structure not only ensures high-speed operation, high breakdown and low collector turn-on voltages, but also provides pin photodiode (PD) layers suitable for high-speed and high-sensitivity operations. The FPIGA DHBT collector structure is primarily composed of relatively thick undoped, thin p +- and thin n +-InGaAs layers, and a lightly doped N-InP layer. They form a potential notch at the InGaAs InP interface at a relatively long distance from the base-collector interface, which effectively suppresses the current blocking effects arising from the conduction band discontinuity at the InGaAs InP interface. The thin p +-InGaAs layer also raises the conduction band in the collector to enhance the ballistic transport of electrons. Breakdown voltage increases because the major part of the potential change at high collector bias occurs in the N-InP layer. The layer compatibility of both the high-performance DHBTs and high-speed PDs enables us to easily manufacture optoelectronic integrated circuits (OEICs). A 1.6 × 4.6- μm 2 emitter FPIGA DHBT shows a current gain cutoff frequency, f T , of 160 GHz and a maximum oscillation frequency, f max , 162 GHz. The f T value reaches 124 GHz at low V CE of 0.65 V owing to the suppressed electron blocking effect. A small FPIGA DHBT with a 0.6 × 1.6- μm 2 emitter operates with 118 GHz f T and 148 GHz f max at an I C as low as 1 mA. The breakdown voltages of the DHBTs are high enough for any high-speed IC applications. A photoreceiver OEIC comprising a pin PD and an amplifier implemented with the FPIGA DHBTs operates error free up to 10 Gbit/s for 1.55 μm wavelength NRZ signals. For electrical inputs, the amplifier provides a transimpedance of 47.2 dBΩ with 3 dB bandwidth of 23 GHz although it has a disadvantage of parasitic capacitance of the pin PD.

A proposed collector design of double heterojunction bipolar transistors for power applications

A new collector design for the AlGaAs-GaAs double heterostructure bipolar transistor (DHBT) is proposed, analyzed, and simulated. The base-collector junction is linearly graded and terminated with a highly doped thin layer to offset the adverse alloy grading electric field. Simple analytical formulas are derived to facilitate the implementation of the design. A proof-of-principle simulation has been carried out for an X-band AlGaAs-GaAs power DHBT to confirm the design and the derived formula. The simulation shows the breakdown voltage can be increased from 30 V to about 45 V while the critical current density is about the same. It is also shown that, unlike other refined DHBT structures, the proposed structure does not require critical control in the fabrication of the base-collector junction. >

High-speed InP/InGaAs double-heterostructure bipolar transistors with suppressed collector current blocking

InP/InGaAs double-heterostructure bipolar transistors (DHBTs), incorporating a new collector structure featuring ‘‘pn pair doping’’ in the heterointerface vicinity, have been fabricated using a low-pressure metalorganic chemical vapor deposition (MOCVD) method. These transistors provide high collector current densities over 1×105 A/cm2, indicating the successful suppression of current blocking. S-parameter measurements determine the high current gain cutoff frequencies of 130 GHz. These values favorably compare with those of conventional InGaAs-collector HBTs fabricated for comparison, suggesting that the InP collectors have excellent electron transport properties.

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

The Letter 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 8 V. The DC gain decreased with decreasing temperature whereas the ideality factors increased.

Breakdown-speed considerations in InP/InGaAs single- and double-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-AA-thick collector. Nongraded DHBTs can be optimized to perform better in terms of speed-breakdown tradeoffs provided that a high collector doping is used. >

InGaP/GaAs/InGaP double heterostructure bipolar transistors with carbon-doped base grown by CBE

Carbon-doped InGaP/GaAs/InGaP double heterostructure bipolar transistors with 25 Å setback layer are grown by chemical beam epitaxy. Transistors with nonalloyed base contacts show a very high common emitter current gain of 120 and very low collector saturation voltage of 75 mV at room temperature.

Simulation and experimental study of Zn outdiffusion during epitaxial growth of a double heterostructure bipolar transistor structure

A model is developed describing Zn outdiffusion during epitaxial growth of a Double Heterostructure Bipolar Transistor (DHBT) structure. This model is used for the design of the highly p-doped base layer. Experimental results confirm the calculated doping profiles.

Application of Localized Zn Diffusion across Heterointerfaces for the Realization of a Compact High‐Speed Bipolar Driver Circuit on InGaAsP / InP

In this paper a model is proposed explaining the mechanism of Zn diffusion across heterointerfaces. The model is based on the interstitial‐substitutional diffusion mechanism. Employing a repetitive algorithm Zn diffusion across heterointerfaces has been simulated such that the evolution of Zn diffusion in time can be calculated. As an application Zn diffusion across three heterointerfaces involved in the fabrication of invertible double heterostructure bipolar transistors (DHBT) (Zn from the gas phase at 823 K) has been numerically calculated. Good agreement between simulated results and experimental data was achieved. The invertible DHBTs were used to build a compact driver circuit with the three transistors involved being interconnected by a common subcollector layer. A current modulation capability up to 2.6 Gbit/s with output currents of more than 50 mA and an ac transconductance of 120 mS were obtained.

Structure, properties and applications of GexSi1-x strained layers and superlattices

The first successful pseudomorphic GexSi1-x strained layers on Si were grown in Germany in 1975. The extensive work that has been done on the production, properties and application of GexSi1-x strained layers and superlattices over the last fifteen years is described in this review. Values of critical layer thickness of the strained layers predicted by equilibrium theories are discussed and compared with experimental results. For x<0.6 the observed values are much larger than the theoretical values. The possible causes of this discrepancy are investigated and it is concluded that the layers must be metastable due to an energy barrier for the production of dislocations. Critical layer thicknesses of superlattices are also discussed and symmetrically strained superlattices are described. Results of band structure calculations of the strained layers and superlattices are given. Strain causes a large reduction in the fundamental indirect band gap of the Si/Ge alloy. Calculated band line-ups at the strained layer-substrate interface are compared with experiment. Modifications in the band structure due to strain have considerable effect on the optical and transport properties of the strained layers. Observed luminescence, photoconductivity and mobility are compared with predictions, taking strain into account. In the case of superlattices, band structure is further modified by zone folding. Superlattice structures which can produce a direct band gap are discussed. Raman scattering has proved a valuable tool for characterizing strained layers and superlattices. In the case of GexSi1-x strained layers, the Raman spectrum shows phonon lines shifted by strain. In the case of superlattices, additional lines due to zone folded LA phonons are observed. Raman measurements may be used to determine strain, thickness of a period and quality of interfaces. This review places emphasis on the use of Si/Ge strained in layers in Si-technology-based integrated circuits. The devices which have been fabricated to exploit properties of these layers include double heterostructure bipolar transistors, optical detectors, modulation doped field-effect transistors and mixed tunnelling avalanche transit time diodes. Progress made in the last 18 months has been rapid; a transistor with a cut-off frequency of 75 GHz was recently fabricated and this device has considerable promise.

The combined effects of strain and heavy doping on the indirect band gap of Si and Ge xSi 1− x alloys

Both boron and phosphorus cause shrinkage in the lattice constant of Si. Therefore heavily doped Si:B and Si:P epitaxial layers grown on intrinsic Si substrates are strained provided no misfit dislocations are present at the interface. The strain is a biaxial extension and has a hydrostatic component as well as a shear component. Ge x Si 1− x layers matched to Si or Ge substrates are also strained. The strain causes band splitting which in its turn causes narrowing of the fundamental indirect band gap of the layers. The hydrostatic component also causes band gap shrinkage. In addition the strain modifies and increases the band gap narrowing due to heavy doping effects as compared with the unstrained case. In this paper the narrowing of the fundamental indirect band gap due to the combined effects of strain and heavy doping is calculated for Si and Ge x Si 1− x epilayers. The results are used to explain the photoluminescence of heavily doped Si:B strained layers grown by MBE on intrinsic Si substrate. It is shown that the band gap narrowing due to heavy doping in strained Ge x Si 1− x layers must be taken into account in the design of double heterostructure bipolar transistors with Ge x Si 1− x base layers.

GaInAs/GaInAsP/InP heterostructure bipolar transistors with very thin base (150 Å) grown by chemical beam epitaxy

It is demonstrated that chemical beam epitaxy (CBE) is suitable for growing high quality GaInAs(P)/InP heterostructure bipolar transistors. Step-graded double-heterostructure bipolar transistors with very thin base (150 Å) and very high p doping (∼5×1019 cm−3), and with an added ‘‘grading layer’’ of 200 Å GaInAsP (Eg =0.94 eV) between the GaInAs/InP base-collector junction, have shown good current drive capability and excellent current gain ( β=2500). In addition, CBE-grown standard single-heterostructure bipolar transistors with a 1000 Å base and 2×1018 cm−3 p doping are characterized by high gain, β∼3500, which is only weakly dependent on the collector current.

GexSi1−x strained-layer heterostructure bipolar transistors

Double heterostructure bipolar transistors with the base region consisting of a p-Ge0.5Si0.5 strained-layer superlattice have been grown by molecular beam epitaxy. At a wavelength of 1.3 μm, optical gain as high as 52 has been achieved in two-terminal phototransistors. The large photocurrent is inferred to be a product of the transistor gain, on the order of 20, and avalanche multiplication. A differential current gain of 10 has been obtained in the three-terminal bipolar transistors. The incorporation of a narrow band-gap GexSi1−x superlattice base is expected to result in higher emitter injection efficiency as compared to Si bipolar transistors.

Emitter-collector reciprocity of double heterojunction bipolar transistors: A three-dimensional analysis and proof for transistors with heavily doped and degenerate base regions

A three-dimensional analysis of the validity of emitter-collector reciprocity of double heterostructure bipolar transistors with heavily doped and degenerate base regions has been carried out. The analysis is based on current-density relations of Marshak and Van Vliet [Solid-State Electron. 21, 429 (1978)], an effective intrinsic carrier concentration derived in terms of band-gap narrowing and the effect of Fermi–Dirac statistics, and p-n product derived by considering potential barriers and related properties of heterostructures. The analysis indicates that the bipolar reciprocity holds under low-level injection even when parameters such as band-gap narrowing of the band, and mobility, diffusivity, lifetime, and recombination velocity, etc., of the carriers depend on spatial coordinates, and the carrier concentrations are described by Fermi–Dirac statistics. The analysis is general enough to be applicable to both n-p-n and p-n-p heterostructure and homostructure bipolar transistors.

High-speed self-aligned InP/GaInAs double heterostructure bipolar transistor with high current-driving capability

A fully self-aligned InP/GaInAs double heterostructure transistor has been fabricated using a substitutional emitter process. The small-signal current gain was typically 10–30 with a fT of 27 GHz. The maximum fT = 27 GHz occurred at current densities of 7 × 104 A cm−2, and the associated fmax was 20 GHz, the highest value obtained for InP-based bipolar transistors to date.