Single Heterojunction Bipolar Transistors Research Articles

High current gain AlGaAs/GaAs heterojunction bipolar transistor grown by molecular beam epitaxy

The fabrication and characteristics of Npn AlGaAs/GaAs single heterojunction bipolar transistors (HBTs) with an emitter edge-thinning structure have been studied. A new and simple selective wet etching method was used to make the emitter edge-thinning structure. The best device obtained shows a common emitter differential current gain of 8700. To our knowledge, this is the highest current gain of AlGaAs/GaAs HBT grown by MBE reported to date. The Gummel plot of this device is analyzed and compared with another HBT which has no emitter edge-thinning structure and was fabricated on the same epiwafer. It is found that the base current of the emitter edge-thinning device is one-tenth smaller than that of the controlled device. In low current region, the effect of emitter edge-thinning structure is even more significant. Because of the reduction of 2-kT surface recombination current, the emitter edge-thinning device reveals its intrinsic 1-kT base current in high current region.

Hot-electron electroluminescence in AlGaAs/GaAs heterojunction bipolar transistors

When biased in the active region at high collector voltages, AlGaAs/GaAs single heterojunction bipolar transistors have been observed to emit light in the 1.1–2.5 eV energy range. The spectral distribution of the emitted radiation results from the superimposition of (i) two peaks at about 1.4 and 2.1 eV, due to band-to-band recombination of cold electrons and holes, and (ii) a nearly exponential tail due to hot-electron-induced electroluminescence, whose intensity depends on reverse collector-base voltage. Moreover, a linear correlation has been found between the intensity of the hot-electron-induced electroluminescence and the current generated by impact ionization.

Base recombination of high performance InGaAs/InP HBT's

Summary form only given. The authors have measured the gain of InGaAs HBTs (heterojunction bipolar transistors) as a function of base doping, with Zn and Be, using MOCVD (metal-organic chemical vapor deposition), and with C, using gas source MBE (molecular beam epitaxy), in the range of 5*10/sup 18/ to 8*10/sup 19/. Large area devices were measured at 2 kA/cm/sup 2/, where DC gain is saturated. Single HBTs, and double HBTs with graded base-collector junctions, were compared. Zn doping gave the highest figure of merit (HFE/R/sub bs//sup 2/), but the tendency for Zn to diffuse at high concentrations produced low collector breakdown voltage. Be doping resulted in high V/sub bc/>6 V at very low r/sub o/, >

Characterisation of GaInP/GaAs double heterojunction bipolar transistors with different collector designs

The characteristics of InGaP/GaAs:C double-heterojunction bipolar transistors (DHBTs) with different collector layer designs are investigated and compared with those of a single heterojunction bipolar transistor. By inserting highly-doped n-type GaAs and InGaP layers in the collector, current saturation characteristics of a DHBT, comparable to those of a single heterojunction bipolar transistor, are achieved. The breakdown voltage of the DHBT was substantially higher than that of a single-heterojunction bipolar transistor with the same collector doping and thickness.

Large-signal nonquasi-static model for single and double heterojunction bipolar transistors

A large-signal nonquasi-static model for heterojunction bipolar transistors (HBTs) is presented. Using this model, the turn-on and turn-off transient characteristics were simulated. The simulation results obtained using this model and that of Gummel-Poon model are compared with the results obtained numerically. This comparison shows that our model can more accurately predict the device transient performance. The model accuracy can be improved even further if nonquasi-static junction capacitance models are used. Using our model, it will be possible to simulate digital circuits in the gigabit range.

Intrinsic gate delay of GaAs/AlGaAs single and double heterostructure I 2 L circuits

An analytical model is used to compare minimum gate delay in GaAs/AlGaAs single and double heterostructure I/sup 2/L circuits. It is shown that for a moderate base doping level a single heterojunction bipolar transistor incorporated in Schottky coupled I/sup 2/L circuit offers the smallest delay.

InGaP/GaAs single- and double-heterojunction bipolar transistors grown by organometallic vapour phase epitaxy

InGaP/GaAs single-heterojunction bipolar transistors (HBTs) and double-heterojunction bipolar transistors (DHBTs) grown by organometallic vapour phase epitaxy are reported. A current gain beta =40 was obtained for 90 mu m diameter HBT devices at a base-collector bias of 0 V. The base carbon-doping concentration for the devices was 2*1019 cm-3 and the sheet resistivity ( rho s) of the base layer was 600 Omega / Square Operator . For the DHBTs, a current gain beta =27 was obtained for a base-collector bias of 2 V. The carbon doping concentration in these devices was 8*1018 cm-3 with rho s=1400 Omega / Square Operator . This represents the first successful fabrication of DHBTs for this material system.

InGaP/GaAs based single and double heterojunction bipolar transistors grown by MOMBE

Carbon-doped based InGaP/GaAs single and double heterojunction bipolar transistors (HBTs) grown by gas-source metal organic molecular beam epitaxy (MOMBE) are reported. Large area devices (emitter diameter 70μm) exhibited gain of 25 for high injection levels at a base doping of 5 × 1019 cm-3. Ideality factors (<1.1) were obtained for both emitter-base and base-collector junctions in both single (SHBT) and double (DHBT) heterojunction devices. Vceos of 12 and 19V for SHBTs and DHBTs, respectively, were measured.

InGaP/GaAs Based Single and Double Heterojunction Bipolar Transistors Grown by MOMBE

Carbon-doped base InGaP/GaAs single and double heterojunction bipolar transistors (HBTs) grown by gas-source Metal Organic Molecular Beam Epitaxy (MOMBE) are reported. Large are devices (emitter diameter 70 μm) exhibited gain of 25 for high injection levels at a base doping of 5 × 1019 cm−3. Ideality factors (&lt;1.1)were obtained for both emitter-base and base-collector junctions in both single (SHBT) and double PHBT) heterojunction devices. Vceo's of 12 V and 19 V for SHBTs and DHBTs respectively were measured.

AlGaAs/GaAs heterojunction bipolar transistor with a two-dimensional electron gas emitter

We report the operation of the first two-dimensional electron gas (2-DEG) emitter heterojunction bipolar transistor. This device, which was grown by molecular beam epitaxy, incorporates an undoped GaAs spacer between the emitter and base of a standard AlGaAs/GaAs single-heterojunction bipolar transistor. The introduction of the spacer layer causes the formation of a 2-DEG at the AlGaAs/GaAs interface. This 2-DEG defines the emitter side of the junction and produces an emitter-base characteristic similar to that of the collector GaAs homojunction. Using a 300 Å GaAs spacer, offset voltages as low as 30 mV have been attained. These devices also exhibit current gains greater than 10 at emitter current densities of 3 A/cm2 and gains up to 400 in the high current density regime.

AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) prepared by molecular beam epitaxy

A novel AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) has been fabricated and demonstrated. The problems of conventional single heterojunction bipolar transistors (SHBTs) such as graded Al x Ga 1- x Ax emitter and the precise alignment of emitter-base junction are avoided. The proposed HEBT device exhibits significant advantages as (i) ease of fabrication, (ii) extremely small collector offset voltage. The common-emmiter current gain up to 180 with an offset voltage about 80 mV has been obtained in the nonoptimized device. Furthermore, an interesting controllable S-shaped negative-differential-resistance (NDR) phenomenon is observed under reverse operation mode. Therefore, the proposed HEBT may be employed as a multiple-function device which provides the transistor and switch actions on the same wafer, simultaneously.

DC conduction and low-frequency noise characteristics of GaAlAs/GaAs single heterojunction bipolar transistors at room temperature and low temperatures

The DC conduction and low-frequency noise characteristics of GaAlAs/GaAs single heterojunction bipolar transistors (HBTs) have been investigated at room temperature and at temperatures down to 5 K. The collector current dependence of the current gain was investigated at various temperatures. The low-frequency noise characteristics exhibit both 1/f and generation-recombination components. The noise characteristics are sensitive to changes in base current and insensitive to changes in collector-emitter voltage, thus suggesting that the noise source is located in the vicinity of the emitter-base heterojunction. The noise spectrum follows a simple model based on minority carrier trapping effects at the heterointerface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Collector-emitter offset voltage in heterojunction bipolar transistors

Collector-emitter offset voltage in heterojunction bipolar transistors is studied in detail. Based on an in-depth analysis of junction characteristics at zero collector current, a general model for offset voltage applicable to homojunction, single heterojunction and double heterojunction bipolar transistors is obtained. For an abrupt SHBT, the conduction band discontinuity at emitter-base heterojunction is found to be the main cause of large offset voltages. For DHBT's it is found that even when emitter and collector base junctions are identical in all respects, they will have an offset voltage with a magnitude dependent on the current gain of the transistor. Appropriate grading of emitter-base junction is shown to reduce the offset voltage in HBT's to values obtained in homojunction bipolar transistors.

Gummel-Poon model for single and double heterojunction bipolar transistors

An analytical model for single and double heterojunction bipolar transistors has been developed by employing the concepts of the Gummel-Poon model. The equations for injected minority carrier concentrations are developed based on the thermionic diffusion theory. Linking current and total charges in the base are calculated. The Early voltages are treated as functions of the applied voltages rather than as constants. Tunnelling effect has been considered for abrupt heterojunctions. The resemblance of this model with the SPICE BJT model makes it easy to implement it in SPICE.

Physics-based large-signal heterojunction bipolar transistor model for circuit simulation

A comprehensive single heterojunction bipolar transistor (HBT) model suited for circuit simulation is presented. The model is developed in the Gummel-Poon homojunction bipolar transistor model tradition, but adds important heterostructure device physics as well as physical properties of 3 or 4 compound materials such as AlGaAs and GaAs. In contrast to the existing HBT models, which use the Gummel-Poon model and fit HBT experimental data by optimising a large pool of parameters extracted from HBT measurements, the present physics-based model requires only the knowledge of the device make-up (such as the doping concentration and layer thickness) and the material parameters (such as the energy bandgap and electron affinity). Comparisons between the model and measured dependencies for AlGaAs/GaAs/GaAs HBTs on important device specifications such as the DC current/voltage characteristics, DC current gain, and cutoff frequency are included.

Photon emission from avalanche breakdown in the collector junction of GaAs/AlGaAs heterojunction bipolar transistors

The base-collector junction of GaAs/AlGaAs single heterojunction bipolar transistors has been observed to emit light at avalanche breakdown. The spectral distribution curve exhibits broad peaks at 2.03 and 1.43 eV, with the intensities dependent upon the reverse current. These observations suggest that electrons, excited to the upper conduction band by the field, lose their energy by impact ionizing electron-hole pairs and producing the 2.03 eV light, which corresponds to the threshold energy for electron impact ionization. The band-edge emission is the result of direct-gap free-carrier recombination and self-absorption of the high-energy transition.

Analytical base-collector heterojunction capacitance model including collector current effects

The base-collector heterojunction space-charge-region capacitance of double heterojunction bipolar transistors is treated. This capacitance cannot be modeled as the conventional heterojunction depletion capacitance because it is heavily influenced by the collector current, which is neglected in the depletion capacitance model. The analysis includes heterojunction effects as well as high current phenomena such as base pushout and space-charge-limited flow. Large discrepancies are found when comparing the present model with the depletion model at high current densities. Comparison of the base-collector junction capacitances calculated from a single heterojunction bipolar transistor and a double heterojunction bipolar transistor is also included.

AlGaAs/GaAs single heterojunction bipolar transistors grown on InP by molecular beam epitaxy

AlGaAs/GaAs single heterojunction bipolar transistors grown on InP substrates by molecular beam epitaxy have been fabricated and tested. An eight-period 25 Å/25 Å In0.53Ga0.47As/GaAs strained-layer superlattice is incorporated in the buffer structure to reduce dislocation propagation to the active region. Small-signal common emitter current gains of about 20 and 30 at a collector current density of 2×103 A/cm2 have been obtained for devices on InP as compared to about 60 and 150 for those on GaAs in structures with base thickness of 0.12 μm doped with Be to 1×1019 and 1×1018 cm−3, respectively. Current densities as high as 1×104 A/cm2 have been achieved in these devices with emitter area of 50×50 μm2 without degradation, demonstrating the excellent stability of this material. From the collector current dependence of the current gain, ideality factors of 1.3 and 1.2 for the emitter junctions have been obtained for devices on InP and GaAs, respectively.

Fully self-aligned microwave InP/GaInAs single heterojunction bipolar transistors

Fully self-aligned InP/GaInAs single heterojunction bipolar transistors have been fabricated using a polyimide layer for the base-emitter contact separation. A common emitter current gain cutoff frequency fT = 46 GHz and associated fmax = 24 GHz were derived from the S-parameter measurements at a collector current density of 1.5 × 105 A/cm2.

Abrupt interface AlGaAs/GaAs heterojunction bipolar transistors: Carrier heating and junction characteristics

We have fabricated and characterized a series of abrupt interface Npn AlGaAs/GaAs single heterojunction bipolar transistors in which the aluminum arsenide mole fraction in the emitter has been varied in the range 0% to 55%. Tunneling through the spike in the emitter conduction band is shown to be important. It affects the initial energy of carriers that are injected into the base, their effective mass distribution, and also the collector turn-on voltage. Hot electron injection heats the minority carriers in the base. In an Al0.35Ga0.65As emitter device held at room temperature we have optically measured a carrier temperature Tc=640 K. From diffusive transport theory it follows that the carrier heating reduces the base transit time by 70%. The elevated carrier temperature in this device is shown to be confirmed by the gain (hFE=3500). The gains of all the other devices are limited by imperfect injection efficiencies. Although electroluminescence (EL) spectra reveal that hole injection into the bulk of the emitter takes place in low aluminum composition structures, space-charge recombination is shown to be a more important mechanism. Appendices present Richardson’s constant for AlGaAs as a function of composition and the derivation from EL spectra of the ratio of electron-to-hole current across a heterojunction.