Base-collector Heterojunction Research Articles

Comparison of the performance for InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT

The characteristics of a double heterojunction bipolar transistor(DHBT) depend closely on the type of band alignment structure at the hetero-interface between emitter-base(E-B) heterojunction and base-collector(B-C) heterojunction. Based on thermionic-field-diffusion model, the comparisons are made of the DC and the RF characteristics between two novel HBTs, that is, InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT, of which the former has a type-I E-B junction and a type-II B-C junction and the later has a type-II E-B junction and a type-II B-C junction. The simulation results show that DHBT with a type-I E-B junction and a type-II B-C junction has much better current driving capability, DC gain and RF performance, although it has a slightly high turn-on voltage.

On the breakdown behaviors of InP/InGaAs based heterojunction bipolar transistors (HBTs)

The breakdown behaviors of InP/InGaAs single heterojunction bipolar transistor (SHBT) and double heterojunction bipolar transistor (DHBT) are studied and demonstrated. By using a composite collector structure at the base–collector heterojunction, the undesired current-blocking effect, switching, hysteresis phenomenon usually found in an InP/InGaAs conventional DHBT are not observed in our DHBT device. Experimentally, as compared with the studied SHBT, the studied DHBT reveals the enhanced breakdown voltages, lower collector leakage current I CO, and smaller electron impact ionization α. Moreover, the temperature-dependent electron impact ionization characteristics and electrical reliability for both devices are also studied. Therefore, the studied DHBT device provides the promise for millimeter-wave and power circuit applications.

Temperature-dependent characteristics of an InP/InGaAs double heterojunction bipolar transistor with a step-graded InAlGaAs collector

The dc and electron impaction ionization characteristics of an InP/InGaAs double heterojunction bipolar transistor with a step-graded InAlGaAs collector structure are studied and reported. From the experiments, the studied device shows a better common-emitter breakdown voltage and lower output conductance at higher temperature operations. Due to the insertion of a step-graded InAlGaAs collector structure at the base-collector heterojunction, the usually observed switching and hysteresis phenomena in InP/InGaAs-based HBTs are not seen in the studied device. The temperature-dependent electron impact ionization characteristics are also investigated. Above all, the studied DHBT device provides the promise for millimeter-wave and power circuit applications.

A New InP/InGaAs Double Heterojunction Bipolar Transistor With a Step-Graded InAlGaAs Collector Structure

An interesting InP/InGaAs double heterojunction bipolar transistor with a step-graded InAlGaAs layer at the base-collector (B-C) heterojunction is fabricated and studied. Simulated results reveal that the potential spike at the B-C heterointerface is completely eliminated. Experimentally, the operation regime is wider than 11 decades in magnitude of the collector current (Ic = 10-12 A to Ic = 10-1 A). Furthermore, the studied device exhibits a relatively high common-emitter breakdown voltage and low output conductance even at high temperature. In the microwave characteristics, the unity current gain cutoff frequency fT = 72.7 GHz and the maximum oscillation frequency f max = 50 GHz are achieved for a nonoptimized device (AE = 6 times 6 mum2).

Improved InP‐based double heterojunction bipolar transistors

This article develops two double heterostructure bipolar transistors (DHBTs) made by low-pressure metamorphic organic chemical vapor deposition (LP-MOCVD). One is a control DHBT with an abrupt base-collector heterojunction (abrupt DHBT) and the other is an improved DHBT with a composite-collector design (composite DHBT). Of the devices with no ledge passivation, the composite DHBT has a high common-emitter current gain, a low offset voltage and voltage-independent collector current characteristics, unlike the abrupt DHBT. The favorable performance of the composite DHBT follows mainly from the optimal collector design, which effectively lowers the potential spike at the base-collector heterojunction. Furthermore, measurements of the composite DHBT with and without n-InP emitter ledges are made. The composite DHBT with emitter ledges has a current gain of 180, which is 44% higher than that of the device with no emitter ledge. The higher current gain is attributable to the lower base surface recombination current in the composite DHBT with a ledge. The effectiveness of the composite-collector design and the emitter ledge process of the presented DHBT is proven. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A monolithic GaAs-based short wavelength smart pixel based on fabricated p–i–n PD, aDHBT and a VCSEL

For the first time a smart pixel that can function as a building block for an optical transceiverwith circular dimensions is fabricated using an InGaP/GaAs double heterojunction bipolartransistor (DHBT) and a GaAs/AlGaAs vertical cavity surface emitting laser (VCSEL). Anovel InGaP DHBT structure based on an abrupt base–collector heterojunction, theδ+-layer composite collector structure, is employed in this work. The DHBTshowed a breakdown voltage of 13 V and a cut-off frequency of 32 GHz atIc = 30 mA. Also a high performance 850 nm infrared VCSEL exhibited athreshold current of 3.5 mA with a maximum optical output of 4.8 mW atIc = 20 mA and forward voltage of 1.8 V. The detector, comprising the base-to-collectorjunction of the DHBT as a p–i–n photodiode (PD), produced a photocurrent of180 µA for a given input power of 0.3 mW.

RF power characteristics of SiGe HBTs at cryogenic temperatures

This paper investigates the temperature dependence (from 77 to 300 K) of dc, ac, and power characteristics for n-p-n SiGe heterojunction bipolar transistors (HBTs) with and without selectively implanted collector (SIC). In SiGe HBTs without SIC, the valance band discontinuity at the base-collector heterojunction induces a parasitic conduction band barrier while biasing at saturation region and high current operation at cryogenic temperatures. This parasitic conduction band barrier significantly reduces the current gain and cutoff frequency. For transistors biased with fixed collector current, the measured output power, power-added efficiency, and linearity at 2.4 GHz decrease significantly with decreasing operation temperatures. The temperature dependence of output power characteristic is analyzed by Kirk effect, current gain, and cutoff frequency at different temperatures. The parasitic conduction band barrier in SiGe HBTs with SIC is negligible, and thus the device achieves better power performance at cryogenic temperatures compared with that in SiGe HBT without SIC.

English

The cutoff frequency performance of an NPN Si/SiGe/SiGe single-heterojunction bipolartransistor (SiGe SHBT) at high collector current densities has been analysed using a 2-D MEDICIdevice simulator. A conventional NPN Si/SiGe/Si double-heterojunction bipolar transistor(SiGe DHBT) having uniform 20 atomic per cent of germanium in the base region has beeninvestigated for comparison. The analysis shows the formation of a retarding potential barrierfor minority carrier electrons at the base-collector heterojunction of the DHBT structure. Whereas,the base-collector homojunction of the SiGe SHBT structure, having a uniform 15 atomic percent of germanium profile in its base and collector, inhibits the formation of such a retardingpotential barrier, the SHBT structure with a base-collector homojunction shows an improvedcutoff frequency at high collector current density in comparison with conventional SiGe DHBT,which makes it more promising for high speed, scaled down, field-specific applications.

Temperature-dependent dc characteristics of an InGaAs∕InGaAsP heterojunction bipolar transistor with an InGaAsP spacer and a composite-collector structure

The temperature-dependent dc characteristics of an interesting heterojunction bipolar transistor with an InGaAsP spacer and an InGaAs∕InGaAsP composite-collector structure are studied and demonstrated. By employing the intermediate band-gap In0.72Ga0.28As0.61P0.39 material at the emitter-base and base-collector heterojunction, the electron blocking effect is effectively eliminated. The studied device gives the promising dc performances including the small offset and saturation voltages without degrading the breakdown behaviors. The typical incremental current gain of 114 and the maximum dc current gain of 118 are obtained. It is worthwhile to note that the desired current amplification over 11 decades of the magnitude of collector current IC is obtained in the studied device. Moreover, the switching or hysteresis phenomenon usually observed in InP-based devices is not seen in the studied device.

An analytical study of current-voltage characteristics and breakdown performance of GaInP∕GaAs composite collector double heterojunction bipolar transistor

An analytical model taking into account the nonlocal dead-space effects is developed to study the dc characteristics and avalanche multiplication of GaInP∕GaAs double heterojunction bipolar transistor (DHBT) incorporating composite collector designs. The dependence of the turn-on characteristics and the multiplication onset of the HBT on the device composite layer thickness and doping densities are investigated. In this paper, optimum combinations of composite parameters are presented to obtain zero spike effect in the base-collector heterojunction conduction band and to improve output breakdown voltages. The model is then applied to the GaInP∕GaAs DHBT with AlGaAs in the composite collector, which is found to have good I-V characteristics and high operating voltage range before the onset of avalanche multiplication.

Investigation of Breakdown and DC Behavior in HBTs With (Al,Ga)As Collector Layer

We report on the realization of an InGaP-GaAs-based double heterojunction bipolar transistor with high breakdown voltages of up to 85 V using an Al/sub 0.2/Ga/sub 0.8/As collector. These results were achieved with devices with a 2.8 μm collector doped to 6×10/sup 15/ cm/sup -3/ (with an emitter area of 60×60 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). They agree well with calculated data from a semi-analytical breakdown model. A /spl beta//R/sub SBI/ (intrinsic base sheet resistance) ratio of more than 0.5 by introducing a 150-nm-thick graded Al-content region at the base-collector heterojunction was achieved. This layer is needed to efficiently suppress current blocking, which is otherwise caused by the conduction band offset from GaAs to Al/sub 0.2/Ga/sub 0.8/As. The thickness of this region was determined by two-dimensional numerical device simulations that are in good agreement with the measured device properties.

Study of Cutoff Frequency at High Collector Current Density in SiGe Single-Heterojunction Bipolar Transistor

The cutoff frequency performance of an NPN Si/SiGe/SiGe Single-heterojunction bipolar transistor (SiGe SHBT) at high collector current densities has been analyzed using a 2-dimensional MEDICI device simulator. A conventional NPN Si/SiGe/Si Double-heterojunction bipolar transistor (SiGe DHBT) having uniform 14%Ge in the base region has been investigated for comparison. The analysis shows the formation of a retarding potential barrier for minority carrier electrons at the basecollector heterojunction of the DHBT structure. Whereas, the base-collector homojunction of the SiGe SHBT structure, having a uniform 14%Ge profile in its base and collector, inhibits the formation of such a retarding potential barrier. The SHBT structure with a base-collector homojunction shows an Improved cutoff frequency at a high collector current density in comparison with conventional SiGe DHBT, which makes it more promising for high speed, scaled down, field-specific applications.

Implementation of reduced turn-on voltage InGaP HBTs using graded GaInAsN base regions

InGaP/GaInAsN double heterojunction bipolar transistors (HBTs) with compositionally graded bases are presented which exhibit superior dc and radio frequency performance. Reducing the average base layer energy gap and optimizing the emitter-base (e-b) and base-collector (b-c) heterojunctions leads to a 100-mV reduction in the turn-on voltage compared to a baseline InGaP/GaAs process. Simultaneously grading the base layer energy band-gap results in over a 66% improvement in the dc current gain and up to a 35% increase in the unity gain cutoff frequency. DC current gains as high as 250 and cutoff frequencies of 70 GHz are demonstrated. In addition, the InGaP/GaInAsN DHBT structure significantly reduces the common emitter offset and knee voltages, as well as improves the dc current gain temperature stability relative to standard InGaP/GaAs HBTs.

Theoretical investigation of an InGaP/GaAs heterostructure-emitter bipolar transistor with a wide-gap collector

We theoretically analyse the performance of an InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) with a wide-gap collector. Using an exact simulation, we report on detailed calculations and studies including majority-carrier and minority-carrier profiles, recombination-rate distributions, and dc and ac performances. By introducing an undoped GaAs spacer and a heavily doped transition layer into the conventional base–collector heterojunctions, the field across the inserted layers is high enough to pull down the potential spike drastically; thus the knee-shaped characteristics and reach-through effect are not observed. Moreover, the base–emitter (B–E) structure, which we have used, contains an effective p–n homojunction and a hetero-confinement layer to substantially reduce the potential spike at the B–E junctions. Therefore the studied device has exhibited a relatively smaller offset voltage and higher current gain than those of a conventional heterojunction bipolar transistor. The simulated results particularly reveal that a proposed HEBT with an appropriately designed device structure exhibits higher efficiency, lower offset voltage (≤30 mV), lower saturation voltage (≤0.5 V), uniform current gain (∼25), lower operated voltage, higher breakdown voltage and improved characteristics as compared to those obtained from a conventional double heterojunction bipolar transistor structure.

High-speed InGaP/InGaAsN/GaAs NpN double heterojunction bipolar transistors with low turn-on voltage

A current gain β of 23 is demonstrated from a small-area NpN GaAs- based double heterojunction bipolar transistor (HBT) using a low band-gap InGaAsN material (lattice matched to GaAs with an energy band gap E G of 1.2 eV) as the base layer. An improved band-gap engineering design at both emitter–base and base–collector heterojunctions in this GaAs-based HBT structure allows significant turn-on voltage reduction up to 270 mV compared to conventional InGaP/GaAs HBTs, while attaining high-speed performance. Self-aligned devices with emitter active area of 3×5 μm 2 show cutoff frequency f T and maximum oscillation frequency f MAX values of 32 and 52 GHz, respectively. These results demonstrate the strong potential of this novel HBT technology to reduce power consumption in future wireless handsets using the GaAs manufacturing platform.

Characterization of InP/InGaAs double-heterojunction bipolar transistors with tunnelling barriers and composite collector structures

We study and demonstrate the dc performance of two InP/InGaAs double-heterojunction bipolar transistor (DHBTs) with the undoped tunnelling barrier and composite collector structures. Due to the mass filtering effect for holes, a thin InP tunnelling barrier can be used to replace the wide-gap emitter. By varying the thickness of the barrier, distinct collector current ideality factors can be obtained which reveal different injection mechanisms at the emitter. The 4000 Å InP collectors with InP/InGaAs abrupt junctions and InP/InGaAsP/InGaAs step-graded junctions achieve high breakdown voltages of 9.2 and 14.6 V, respectively. Furthermore, the abrupt junction and δ-doping structure eliminate carrier blocking across the base-collector heterojunction more effectively than the step-graded junction. We find that the reduction of the multiplication avalanche of the step-graded junction DHBT leads to the severe self-heating effect. For the abrupt junction DHBT, the dc current gain is almost independent of the perimeter-to-area ratio of the emitter due to the low surface recombination.

Applications of InGaP “Insulator” for High-Breakdown and Low-Offset Voltage Heterostructure Bipolar Transistor

In this work, a new InGaP/GaAs heterostructure transistor with a □-doped wide-gap collector structure has been fabricated successfully and demonstrated. A near-ideal breakdown characteristic and good transistor performance are obtained. These good characteristics are mainly due to the complete elimination of potential spike at emitter-base (base-collector) heterojunction and the employment of wide-gap InGaP material as collector layer. Consequently, the studied device shows a promise for high-speed and large input signal circuit applications.

A new In0.5Ga0.5P/GaAs double heterojunction bipolar transistor (DHBT) prepared by MOCVD

A new In 0.5 Ga 0.5 P/GaAs double heterojunction bipolar transistor (DHBT) with a δ-doped wide-gap collector structure has been grown by a LPMOCVD system. Experimental results show that this device exhibits the advantages of a small offset voltage of 50 mV, a small saturation voltage of I V, and a large breakdown voltage of 20 V with a current gain of 20. These good characteristics are mainly due to the complete elimination of potential spike at emitter-base (E-B) and base-collector (B-C) heterojunction. Consequently, the studied device shows a good promise for high-speed, high-power, lower-power consumption and large input signal circuit applications.

Direct extraction and numerical simulation of the base and collector delay times in double heterojunction bipolar transistors

A new method is presented to evaluate the base and collector transit times, /spl tau//sub B/ and /spl tau//sub C/ in heterojunction bipolar transistors (BBT's) from the phase and magnitude of the common-base current gain, /spl alpha/(/spl omega/), which itself was directly extracted from measured S-parameter data. The method is applied to InGaP/GaAs single and double HBT's. A smaller cutoff frequency in the latter device is attributed to /spl tau//sub B/ and /spl tau//sub C/ due to two effects: trapping of electrons in the conduction band triangular barrier existing at the base-collector (B-C) heterojunction and smaller saturation velocity of electrons in InGaP as compared to GaAs. Finally, a new B-C design of InGaP/GaAs DNBT's is proposed to partially compensate the transit time effects. Numerical simulation of the cutoff frequency demonstrates the superiority of the proposed structure for high-frequency applications.

Base Transit Time in Abrupt GaN/InGaN/GaN and AlGaN/GaN/AlGaN HBTs

Base transit time, τb , in abrupt npn GaN/InGaN/GaN and AlGaN/GaN/AlGaN double heterojunction bipolar transistors (DHBTs) is reported. Base transit time strongly depends not only on the quasi-neutral base width, but also on the low field electron mobility, μn, in the neutral base region and the effective electron velocity, Sc, at the edge of base-collector heterojunction. μn and Sc are temperature-dependent parameters. A unity gain cut-off frequency of 10.6 GHz is obtained in AlGaN/GaN/AlGaN DHBTs and 19.1 GHz in GaN/InGaN/GaN DHBTs for a neutral base width of 0.05um. It is also shown that non-stationary transport is not required to study τb for neutral base width in the range of 0.05um for GaN-based HBTs.