Characteristics Of Heterojunction Bipolar Transistors Research Articles

An Accurate Electro-Thermal Coupling Model of a GaAs HBT Device under Floating Heat Source Disturbances.

Taking into consideration the inaccurate temperature predictions in traditional thermal models of power devices, we undertook a study on the temperature rise characteristics of heterojunction bipolar transistors (HBTs) with a two-dimensional cross-sectional structure including a sub-collector region. We developed a current-adjusted polynomial electro-thermal coupling model based on investigating floating heat sources. This model was developed using precise simulation data acquired from SILVACO (Santa Clara, CA, USA). Additionally, we utilized COMSOL software (version 5.6) to simulate the temperature distribution within parallel power cells, examining further impacts resulting from thermal coupling. The research findings indicate that the rise in current induces modifications in the local carrier concentration, thereby prompting variations in the local electric field, including changes in the heat source's peak location and intensity. The device's peak temperature exhibits a non-linear trend regulated by the current, revealing an error margin of less than 1.5% in the proposed current-corrected model. At higher current levels, the drift of the heat source leads to an increase in the heat dissipation path and reduces the coupling strength between parallel devices. Experiments were performed on 64 GaAs (gallium arsenide) HBT-based power cells using a QFI infrared imaging system. Compared to the traditional temperature calculation model, the proposed model increased the accuracy by 6.84%, allowing for more precise predictions of transistor peak temperatures in high-power applications.

A Compact Macromodeling Method for Characterizing Large-signal DC and AC Performance of InP and GaAs HBTs

In this paper, a compact macromodeling method for characterizing the large-signal characteristics of heterojunction bipolar transistors (HBTs) is proposed and successfully applied to describe the DC and AC performance of InP and GaAs HBT devices. Using the Symbolically-defined Device (SDD) technology, an empirical macro circuit preserving the Spice Gummel-Poon (SGP) intrinsic network and a simplified thermal network is established. The empirical current and charge functions are embedded in the SDD macro circuit network module. Compared with other large-signal models, the proposed model description and the relevant parameter extraction are relatively simpler, and at the same time, this method can maintain high fitting accuracy. To assess the validity and the accuracy of the proposed model, the compact large-signal model is constructed for 1 ㎛ InP HBT and 1 ㎛ GaAs HBT. Based on the complete extraction of the model parameters, excellent consistency is obtained between the measured and modeled results.

Impact of base bias current and incident optical power on the InP/InGaAs heterojunction phototransistor performances

In this article, the optical and electrical properties of NPN InP/InGaAs heterojunction bipolar phototransistor (HPT) are studied by two dimensional semiconductor simulation. The phototransistor is modelled using a numerical method, and the results are presented and discussed. This model is based on heterojunction bipolar transistor (HBT) model with the consideration of the optical beam effect. Responsivity of 12.62 A/W for 1100 nm light is achieved when the thickness of base layer is 50 nm. A good qualitative agreement of the numerical and analytical simulated value of both collector current and responsivity as a function of the wavelength with the existing experimental data was achieved. We present a comparative analysis of our obtained solutions at IB = 5 μA with that simulated at IB = 100 μA and we found that the value of optical power (Popt) giving high injection into a phototransistor at IB = 5 μA is three times higher than that at IB = 100 μA. The effects of both the base bias current and the incident optical power on the device performance are investigated. The simulation results, which are presented and compared at low, ideal and high base bias current, show that the highest photocurrent and optical gain are obtained when the base bias current reaches the ideal region. The HPT optical characteristics such as the electrical characteristics of HBT are affected by the high injection effect (Kirk effect).

The main characteristics of SiGe HBTs at low temperatures

The current-voltage curves (CVC) of n-p-n SiGe heterojunction bipolar transistors (HBT) are considered within the temperature range from minus -195˚С up to 25˚С, produced on the SGB25V technology of IHP. The experimental setup, the measurement technique and the connection features of transistors for elimination of the self-excitation are described. The special attention is paid to the temperature dependences of the static base current gain βF in the common-emitter configuration (CEC) and to the output CVC characteristics of transistor in the CEC.

Quantitative analysis of dc characteristics of Ga0.5In0.5P/GaAs heterojunction bipolar devices

This paper presents quantitative analysis of direct current (DC) characteristics of an N/p+/n Ga0.5In0.5P/GaAs heterojunction bipolar transistor (HBT) using thermionic-field-diffusion model including high current effects such as base push-out, parasitics like emitter resistance and base resistance. These effects play an important role in predicting DC characteristics of HBT. Software was developed to simulate the Gummel plot, current gain, collector–emitter breakdown voltage, and the offset voltage. As per their design, the authors got Ga0.5In0.5P/GaAs heterojunction bipolar transistor fabricated from IQE Inc. The simulated Gummel plot agrees with the experimental data in the complete operating range of applied bias. The current gain, β, of the HBT is found to be ∼100–120. A broad comparison of current gain of various devices was made and analyzed as a function of collector current density. The β of various HBTs were also analyzed in terms of base sheet resistance for three values of collector current density. The breakdown voltage and offset voltage were simulated to be of the order of 10 V and 120 mV, respectively, for the designed device. These values agree with the experimental data. The computed electric field in the base–collector region and the multiplication factor in the avalanche breakdown of the HBT are presented as a function of collector–emitter voltage.

The impact of interface charges at the heterojunction on the carriers transport in abrupt InP/InGaAs heterojunction bipolar transistor

The carriers transport at the base-emitter interface of abrupt heterojunction bipolar transistors (HBTs) is controlled by thermionic emission and tunneling, which depends on the form and height of the energy barriers. The interface charges at the heterojunction disturb the energy barriers, thus bringing about the change of the electrical characteristics of HBT. Based on thermionic-field-diffusion model which combines the drift-diffusion transport in the bulk of the transistor with the thermionic emission and tunneling at the interface, a conclusion can be drawn that the positive interface charges can improve the electrical characteristics of abrupt InP/InGaAs HBT, while the negative interface charges deteriorate the devices.

Figures‐of‐merit genetic extraction for InGaAs lasers, SiGe low‐noise amplifiers, and ZnSe/Ge/GaAs HBTs

AbstractIn this paper, we have successfully developed an intellectual parameter‐extraction methodology on the basis of a genetic algorithm (GA), involving the efficient search‐space separation and local‐minima‐convergence prevention schemes. Via an evolutionary simulation tool complemented with appropriate analytic equations, the enhanced approach has been applied to determine the significant figures‐of‐merit (FoMs), including internal quantum efficiency (ηi) as well as transparency current density (Jtr) of semiconductor lasers, minimum noise figure (NFmin) as well as associated available gain (GA,assoc) of low‐noise amplifiers (LNAs), and DC as well as AC characteristics of heterojunction bipolar transistors (HBTs). For the first time, demonstrated FoM‐extraction results, which coincide well with the actually measured data, for state‐of‐the‐art InGaAs quantum‐well lasers, advanced SiGe LNAs, and abrupt ZnSe/Ge/GaAs HBTs are simultaneously presented to validate this multi‐parameter analysis and robust optimization. Copyright © 2011 John Wiley & Sons, Ltd.

On the RF Properties of Weakly Saturated SiGe HBTs and Their Potential Use in Ultralow-Voltage Circuits

We investigate, for the first time, the feasibility of operating silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in a weakly saturated bias regime to enable ultralow-voltage RF front-end design. Measured dc, ac, and RF characteristics of third-generation high-performance SiGe HBTs operating in weak saturation are presented. Robust RF operation of 0.12 × 6.0 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> SiGe HBTs are demonstrated in a common-emitter configuration at collector-to-emitter voltages above 0.15 V. A noise figure of 1.33 dB and an input third-order intercept point above -8 dBm for a 3-GHz input tone are achieved at 0.30 V. These results have potential implications for RF circuits used in severely power-constrained systems.

Safe Operating Area of GaAs HBTs Based on Sub-Nanosecond Pulse Characteristics

Using a novel sub-nanosecond pulse current-voltage measurement technique, InGaP/GaAs heterojunction bipolar transistors (HBTs) were shown to survive strong impact ionization and to have a much larger safe operating area (SOA) than previously measured or predicted. As the result, an empirical model for impact ionization with both voltage and current dependence was extracted and added to a commercially available HBT model. The modified model could predict the HBT characteristics across the enlarged SOA, as well as the performance of ultra-wideband pulse generators and the ruggedness of continuous wave Class-C power amplifiers.

High-temperature characteristics up to 590 °C of a pnp AlGaN/GaN heterojunction bipolar transistor

We investigated the temperature dependence of the common-emitter I-V characteristics of a pnp AlGaN/GaN heterojunction bipolar transistor (HBT) at temperatures ranging from RT to 590 °C. The HBT operated at 590 °C in air with a current gain of 3. Even at 590 °C, the collector-emitter leakage current was as low as 9 μA at the collector-emitter voltage of 40 V. Although there is no significant degradation of the HBT characteristics only by annealing in air at 400 °C for 2 h, the current gain reduced to 30% of the initial one after the common-emitter operation at 400 °C for 2 h.

Influence of temperature on the characteristics of heterojunction bipolar transistor

Using the noise low-signal model with the help of Volterra’s series apparatus the influence of temperature on non-linear, amplification and noise characteristics of a low-noise microwave amplifier on heterojunction bipolar transistor in various operation modes is analyzed. On the basis of the obtained data practical recommendations on choosing the transistor’s power source under various temperatures to optimize its work are given.

Effect of Mixed-Mode Electrical Stress on High-Frequency and RF Power Characteristics of SiGe Hetero-Junction Bipolar Transistors

In this study, we investigate the hot-carrier stress effects on the high-frequency and RF power characteristics of Si/SiGe hetero-junction bipolar transistors (HBTs). By simultaneously applying a high collector current density and a high collector–base voltage on Si/SiGe HBTs, because hot carriers will be induced; they will then degrade device performance. This is interesting because this stress condition is similar to the DC bias condition of a current source RF power amplifier, termed as the “mixed-mode” stress. We find that not only the high-frequency characteristic is adversely affected by but also the output power performance of Si/SiGe HBTs suffers from this electrical stress. In addition, we found that the degradations of the high-frequency and power characteristics of such HBTs are worse in constant-base-current measurement than in constant-collector-current measurement. We finally examined the degradations in terms of parasitic resistance and the ideality factors of base and collector currents using a large-signal model.

Carrier transport mechanisms of Pnp AlGaN∕GaN heterojunction bipolar transistors

We fabricated Pnp AlGaN∕GaN heterojunction bipolar transistors (HBTs) with various base widths WB and investigated their common-emitter current-voltage characteristics at room temperature to clarify their carrier transport mechanisms. The current gain β increased as WB decreased. The maximum current gain βmax was 40 in a HBT with a WB of 30nm. HBTs with different base widths exhibited almost the same tendency for β to increase with increasing the collector current IC, indicating that the carrier transport mechanism is the same in all the n-GaN base layers. With a low IC, recombination in the emitter-base depletion region is the dominant carrier transport mechanism. β was less affected when IC was high, and the carrier transport was dominated by the minority hole diffusion in the neutral base layer. The minority hole diffusion length obtained from the HBT characteristics agrees well with previous results obtained with electron beam induced current measurements, also indicating that βmax was determined by the minority hole diffusion length in the n-GaN base layer.

Effect of heavy boron doping on the electrical characteristics of SiGe HBTs

A modified version of the Jain–Roulston (J–R) model is developed that takes into account the compensation effect of B to Ge in strained SiGe layers for the first time. Based on this new model, the distribution of the bandgap narrowing (BGN) between the conduction and valence bands is calculated. The influence of this distribution on the transport characteristics of abrupt SiGe heterojunction bipolar transistors (HBTs) has been further considered by using the tunnelling and thermionic emission mechanisms instead of the drift and diffusion mechanisms at the interfaces where discontinuities in energy levels appear. The results show that our modified J–R model better fits the experimental values, and the energy band structure has a strong influence on electrical characteristics.

Temperature-Dependent DC Characteristics of InGaP ∕ GaAs Heterojunction Bipolar Transistors with Different Passivation

Temperature-dependent dc characteristics of heterojunction bipolar transistors (HBTs) without any surface passivation, with sulfur passivation, and with emitter ledge structure were systematically studied and demonstrated. Experimentally, due to the effective suppression of the thermal leakage current and hot-carrier injection around the emitter mesa edge, the device with ledge structure revealed lower base-surface recombination current density as well as better thermal stability and electrical reliability than the devices with/without sulfur passivation.

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.

DC and 1/f noise characteristics of InGaP/InGaAsN/GaAs double heterojunction bipolar transistors

A novel quaternary material of InGaAsN has been proposed as a base layer for GaAs-based double heterojunction bipolar transistors (DHBTs). By utilizing InGaAs as a base material, a lower band gap energy of the base layer in heterojunction bipolar transistors (HBTs) followed by a smaller turn-on voltage can be achieved. The 1/f noise characteristics of HBTs with an InGaAs base layer also show great improvement. Moreover, a smaller band gap base material of InGaAsN latticed-matched to a GaAs substrate can be obtained by incorporating suitable amounts of indium (In) and nitrogen (N) into GaAs base material, and thus enhance turn-on voltage reduction. In this study, dc and flicker noise characteristics of InGaAsN DHBTs are investigated by comparing GaAs and InGaAs DHBTs. The experimental results show that the 1/f noise has been found to depend on Ib as Iγb, where 1.95 < γ < 2.04 for the InGaP/InGaAsN DHBTs with high current gains (β ∼ 60). The 1/f noise of the InGaAsN sample is one order lower than that of the GaAs sample.

High-Performance InGaP/GaAs HBTs With Compositionally Graded Bases Grown by Solid-Source MBE

N-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with compositionally graded In/sub x/Ga/sub 1-x/As (Be doped) bases have been successfully grown by solid-source molecular beam Epitaxy (SSMBE) using a gallium phosphide (GaP) decomposition source. In this paper, the dc and RF characteristics of HBTs with different indium mole fractions in the graded In/sub x/Ga/sub 1-x/As base (x:0 /spl rarr/ ;0.1 and x:0 /spl rarr/ 0.05) are measured to investigate optimum-grading profiles. The measured average current gains, /spl beta/s of a control sample, a 10% graded-base sample and a 5% graded-base sample, are 162, 397 and 362, respectively. To our knowledge, these current gains are the highest values ever reported in compositionally graded-base InGaP/GaAs HBTs with a base sheet resistance R/sub sh/ of /spl sim/200 /spl Omega//sq establishing a new benchmark for InGaP/GaAs HBTs. Furthermore, these compositionally graded-base HBTs show higher unity current/gain cutoff frequency, f/sub T/ and maximum oscillation frequency, f/sub max/. Compared to the control sample with the same base thickness, the base transit time /spl tau//sub B/ of the graded sample is reduced by /spl sim/15% to /spl sim/20% by the induced built-in potential, resulting in an increase of f/sub max/ from 16 to 18.5 GHz in a device with an emitter size of 10/spl times/10 /spl mu/m/sup 2/. Additionally, for the 5% graded-base sample, with a 5/spl times/5 /spl mu/m/sup 2/ emitter region, f/sub T/ and f/sub max/ are 16.3 and 33.8 GHz, respectively, under low-level collector current. These results demonstrate that InGaP/GaAs HBTs with In/sub x/Ga/sub 1-x/As graded-base layers (x:0 /spl rarr/ 0.05) have the potential for high-speed analogue to digital converters.

Reverse Active Mode Current Characteristics of SiGe HBTs

The current characteristics of SiGe heterojunction bipolar transistors (HBTs) operating in the reverse active mode are investigated. It is experimentally shown that the I/sub C/ is identical for the reverse and the forward modes for arbitrary doping and Ge profiles across the base to first order. In contrast, the impact of V/sub BE/ and V/sub CB/ modulation on I/sub C/ is opposite for the two modes, leading to a smaller Early voltage but more ideal collector current for the reverse mode.

Extrinsic Base Regrowth of p-InGaN for Npn-Type GaN/InGaN Heterojunction Bipolar Transistors

The regrowth of p-InGaN as the extrinsic base layer of Npn-type GaN/InGaN heterojunction bipolar transistors (HBTs) significantly improves the ohmic characteristics of the base layer. The specific contact resistance is 7.8×10-4 Ω·cm2 even after the dry etching. This value for a non-alloyed ohmic contact is much better than that for as-grown p-GaN (1.7×10-3 Ω·cm2) and decreased turn-on voltage in the emitter-base diodes, which results in high current gains of up to 2000 and reduced offset voltages in the GaN/InGaN HBTs. These results show that the p-InGaN extrinsic base regrowth is an effective way to improve nitride HBT characteristics.