Comparison of GaInP/GaAs heterostructure-emitter bipolartransistors and heterojunction bipolar transistors

Carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBT's) and heterostructure-emitter bipolar transistors (HEBT's) grown by MOCVD were fabricated. Experimental comparison of HBT's and HEBT's has been made based on the dc and the RF performance. HBT's have higher current gains than those of HEBT's in the high current regime, while HEBT's offer a smaller offset voltage and better uniformity in dc characteristics across the wafer. The current gain and cutoff frequency of the DEBT with a 150 Å emitter set-back layer are comparable to those of HBT's. DC (differential) current gains of 600 (900) and 560 (900) were obtained at a collector current density of 2.5×10⁴ A/cm² for the HBT and HEBT, respectively. The cutoff frequencies are 37 and 31 GHz for the HBT and HEBT, respectively. It is shown that there is negligible contribution of the diffusion capacitance to the emitter capacitance in HEBT's with a thin emitter set-back layer but not with a thick emitter set-back layer. The behavior of HEBT's both in dc and RF characteristics is similar to that of HBT's     

On the short and long term degradation of GaInP/GaAs heterojunction bipolar transistors

This work deals with the short and long term effects of a current stress performed at room temperature on Carbon doped GaInP/GaAs heterojunction bipolar transistors. The investigation has been carried out by means of DC characterizations and low frequency noise (LFN) measurements in the 250 Hz–100 kHz frequency range. During the stress the devices were biased in the forward active region; a collector–emitter voltage of 7.7 V and a collector current density of 2.2×10⁴ A/cm² were imposed. The effect of the stress on the DC and LFN characteristics were compared and discussed in terms of two recombination mechanisms. The discussion points out that both extrinsic and intrinsic recombination processes have to be taken into account in order to justify the short and long term effects of the electrical stress.     

Growth characteristics of hydride-free chemical beam epitaxy and application to GaInP/GaAs heterojunction bipolar transistors

We report on the complete characterization of a hydride- and hydrogen-free chemical beam epitaxy (CBE) process for the realization of GaAs/GaInP heterojunction bipolar transistors. Alternative group V sources tertiarybutylarsine, tertiarybutylphosphine, and trisdimethylaminoarsenic are used instead of traditionally employed AsH₃ and PH₃. A very high degree of reproducibility of growth parameters (fluxes, substrate temperature, doping levels) is demonstrated. Total defect densities lower than 10 def/cm² are routinely obtained. Large-area GaInP/GaAs heterojunction bipolar transistors (HBTs) show a high current gain of 225 for base sheet resistance of 400 ohm/sq. The devices also exhibit excellent high-frequency characteristics. A cut-off frequency of 48 GHz and a maximum oscillation frequency of 60 GHz have been obtained. These results demonstrate the high potential capability of CBE for high-throughput GaInP/GaAs HBT production.     

Choice of epitaxial structure to promote performance and uniformityof GaAs/AlGaAs heterojunction bipolar transistors grown by MOVPE

Numerical simulations with a one-dimensional physical device model are used to investigate the importance of the design of the emitter and base regions of n-p-n GaAs/AlGaAs HBT structures. A structure of optimum gain and speed is determined together with limits for the variations of the aluminum gradings and doping placement. The simulations show that the edge of the base doping on the emitter side has to be controlled within a few nanometers to avoid serious degradations of the current gain and the cutoff frequency. Variation in the position of the base doping relative to the aluminum gradings is a plausible source of the spread in current gain observed in measurements of devices made by metalorganic vapor-phase epitaxy (MOVPE). It is predicted that longer emitter aluminum gradings will reduce the sensitivity to these variations together with the peak values of gain and speed. It is suggested that the grading length be chosen as a compromise between performance and uniformity depending on the accuracy of the manufacturing method and the demands of the application     

An emitter guard-ring structure for GaAs high-gain heterojunction bipolar transistors

An emitter guard-ring structure is adopted for GaAs/AlGaAs heterojunction bipolar transistors (HBT's). The guard ring is added around the central emitter and has nearly the same dc bias as the base, so that the carrier injection as well as the surface recombination at the emitter periphery is blocked. As a result, the current gain at low operating currents is improved remarkably. It remains almost constant at 600 as the collector current is decreased from 20 mA down to 5 µA. This is the best result to date for a GaAs HBT at low currents. This technique also makes it possible to investigate the interface quality without interference from surface effects.     

GaAlAs/GaAs heterojunction bipolar transistors: issues andprospects for application

Issues important for the manufacturing of GaAlAs/GaAs heterojunction bipolar transistors (HBTs) and their prospects for application in various areas are discussed. The microwave and digital performance status of HBTs is reviewed. Extrapolated values of maximum frequency of oscillation above 200 GHz and frequency divider operation at 26.9 GHz are reported. Key prospects for further device development are highlighted     

AlGaAs/GaAs heterojunction bipolar transistors fabricated using a self-aligned dual-lift-off process

This paper describes a self-aligned heterojunction-bipolar-transistor (HBT) process based on a simple dual-lift-off method. Transistors with emitter width down to 1.2 µm and base doping up to 1 × 10²⁰/cm³have been fabricated. Extrapolated current gain cutoff frequency ftof 55 GHz and maximum frequency of oscillationf_{max}of 105 GHz have been obtained. Current-mode-logic (CML) ring oscillators with propagation delays as low as 14.2 ps have been demonstrated. These are record performance results for bipolar transistors. The dual-lift-off process is promising for both millimeter-wave devices and large-scale integrated circuit fabrication.     

GaAs/AlGaAs heterojunction bipolar transistors for integrated circuit applications

Molecular-beam epitaxy (MBE) and ion implantation were used to fabricate GaAs/AlGaAs heterojunction bipolar transistors with buried wide bandgap emitters. Inverted-mode current gains of ∼ 100 were obtained, demonstrating the feasibility of this technology for I²L types of digital integrated circuits.     

Numerical simulation of GaAs/GaAlAs heterojunction bipolar transistors

A numerical analysis program for the 1-dimensional simulation of GaAs/GaAlAs heterojunction bipolar transistors is described. Calculations for a representative transistor structure indicate that a cutoff frequency, ft, of 100 GHz is obtainable. To attain such a high value, the transistor design incorporated a graded-bandgap base region and relatively high emitter doping (5 × 10¹⁷cm^-3), and the device was operated at high current density (5 × 10⁴A/cm²). Transient electron velocity overshoot effects were also included.     

High-frequency characteristics of AlGaAs/GaAs heterojunction bipolar transistors

The fabrication and high-frequency performance of MBE-grown AlGaAs/GaAs heterojunction bipolar transistors (HBT's) is described. The achieved gain-bandwidth product fTis 25 GHz for a collector current density Jcof 1 × 10⁴A/cm²and a collector-emitter voltage VCEof 3 V.fTcontinues to increase with the collector current in the high current density region over 1 × 10⁴A/cm²with no emitter crowding effect nor Kirk effect. The limitation on fTin fabricated devices is found to be caused mainly by the emitter series resistance.     

Fabrication of InGaP/Al/sub 0.98/Ga/sub 0.02/As/GaAs oxide-confined collector-up heterojunction bipolar transistors

A partially oxidized Al/sub 0.98/Ga/sub 0.02/As layer was introduced between the emitter and base of collector-up heterojunction bipolar transistors (C-up HBTs) to suppress the leakage current and improve the current gain. Dependence of device current gain and leakage current on oxidation temperature was investigated. At lower oxidation temperature, the current gain can be effectively improved. Current gain and base sheet resistance were 79 and 203 ohm/sq. for the C-up HBT oxidized at 400/spl deg/C.     

Fabrication and characterization of AlGaAs/GaAs heterojunction bipolar transistors

The fabrication and characterization of MBE-grown AlGaAs/GaAs heterojunction bipolar transistors (HBT's) are described, A Be redistribution profile in the HBT epi-layer at the emitter-base heterojunction interface is investigated using secondary ion mass spectrometry, A relatively high substrate temperature of 650°C during growth can be employed by introducing a 100-Å undoped spacer layer between the emitter and base layer. A simple wafer characterization method using phototransistors is demonstrated for accurately predicting current gain in a three-terminal device. A dc current gain of up to 230 is obtained for the fabricated HBT with a heavy base doping of 1 × 10¹⁹/cm³. A gain-bandwidth product fTof 25 GHz is achieved with a 4.5-µm-width emitter HBT.     

Analytical investigation of dead space effect under near-breakdown conditions in GaInP/GaAs composite double heterojunction bipolar transistors

The dead space effect under near-breakdown conditions in GaInP/GaAs composite collector double heterojunction bipolar transistor (DHBT) is investigated analytically. Using the dead space corrected model, the breakdown voltage is found to decrease with GaAs spacer thickness as reported from experiments. The common-mode emitter IV characteristics for the DHBT are simulated until the onset of multiplication with good agreement with reported experimental results [IEEE Elec. Dev. Lett. 15 (1994) 10]. A proposed optimised structure is simulated with comparably good turn-on I–V characteristics and improved breakdown performance.     

Integration of GalnP/GaAs heterojunction bipolar transistors andhigh electron mobility transistors

Integration of carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs) is demonstrated by growing an HBT on the top of a HEMT. A current gain of 60, a cutoff frequency of 59 GHz and a maximum oscillation frequency of 68 GHz were obtained for a 5×15 μm² self-aligned HBT. The HEMT, with a gate length of 1.5 μm has a transconductance of 210 mS/mm, a cutoff frequency of 9 GHz and a maximum oscillation frequency of 22 GHz. It is shown that the GaInP/GaAs HBT on the HEMT is a simple Bi-FET technology suitable for microwave and mixed signal applications     

Collector-top GaAs/AlGaAs heterojunction bipolar transistors for high-speed digital ICs

GaAs/AlGaAs collector-top heterojunction bipolar transistors with magnesium and phosphorus double-implanted external bases were fabricated. A cutoff frequency of 17 GHz and a gate delay time of 63 ps for DCTL were obtained. These results indicate the potential of collector-top HBTs for high-speed ICs.     

Monte Carlo simulation of AlGaAs/GaAs heterojunction bipolar transistors

A first demonstration of one-dimensional Monte Carlo simulations of AlGaAs/GaAs heterojunction bipolar transistors is reported. The electron motion is solved by a particle model, while the hole motion is solved by a conventional hydrodynamic model. It is shown that the compositional grading of AlxGa1-xAs in the base region is effective to cause the ballistic acceleration of electrons in the base region, resulting in a high collector current density of above 1 mA/µm². The current-gain cutoff frequency fT reaches 150 GHz if the size of a transistor is properly designed. Also shown is the relation between the device performances and the electron dynamics investigated.     

High-frequency output characteristics of AlGaAs/GaAs heterojunction bipolar transistors

A model has been developed which generates the high-frequency i/sub c/-v/sub ce/ output characteristics of bipolar transistors from computed cutoff frequency against current density data. The presented results, which can be used directly for large-signal modelling are the first report of high-frequency output characteristics of bipolar transistors.<>     

High-frequency performance of lattice-strained heterojunction GaInAs/GaAs bipolar transistors

The performance of bipolar devices and circuits in the novel lattice-strained GaInAs/GaAs materials system show an improving trend with increased In composition in the base. An fT of 8 GHz has been measured using an 8 ?m emitter stripe width and 8% In. A small-signal model is presented.     

GaAs/(GaAl)As heterojunction bipolar transistors using a self-aligned substitutional emitter process

This paper describes the first self-aligned heterojunction bipolar transistor (HBT) process which includes ion implantation to reduce the base resistance. With this substitutional emitter technique, the base implant and the emitter contact patterns are defined with the same mask. Arbitrary contact materials can be used allowing optimization of the contact resistances. Transistors with emitter width down to 1.5 µm have been fabricated. Nonthreshold logic (NTL) ring oscillators made with these transistors had propagation delay times down to 27.2 ps. This is the lowest reported to date for bipolar transistors.