Gummel Plots Research Articles

Tunneling‐Related Leakage Currents in Coaxial GaAs/InGaP Nanowire Heterojunction Bipolar Transistors

Herein, a detailed analysis of leakage mechanisms in epitaxially grown nanowire heterojunction bipolar transistors (NW‐HBTs) is presented. Coaxial npn‐GaAs/InGaP core–multishell nanowires are grown via gold‐catalyzed metalorganic vapor phase epitaxy, processed to three terminal devices and electrically characterized. The key for successful NW‐HBT device functionality is the identification of tunneling as the dominant leakage mechanism in highly doped nanowire pn‐junctions. The suppression of forward tunneling currents by adjustment of the tunneling barrier width reduces the junction leakage current density into the nA cm−2 regime, which is further verified by tunneling‐related electroluminescence measurements. In addition, the suppressed tunneling accordingly increases the number of electrons that are injected from the n‐emitter into the p‐base. The latter effect influences the performance of pn‐junction based devices and is found to enable bipolar transistor functionality. Measured common emitter Gummel plots of the NW‐HBT exhibit a current gain of up to 9 and the transistor function is additionally verified by current‐controlled output characteristics.

AlGaN/GaN Heterojunction Bipolar Transistor With Selective-Area Grown Emitter and Improved Base Contact

We report AlGaN/GaN n-p-n heterojunction bipolar transistors (HBTs) on sapphire substrates with selective-area grown AlGaN emitters by metal–organic chemical vapor deposition. Metal–semiconductor contact on the external p-GaN base layer shows ohmic characteristics thanks to the dry-etching-free process of base–emitter junction. As a result, the maximum current gain $\beta $ is around 90 calculated from the Gummel plot of a ${20}\times {20}\,\,\mu \text{m}^{{2}}$ HBT device. Common-emitter ${I}$ – ${V}$ family curves exhibit offset voltage $({V} _{\text {offset}}) V and knee voltage $({V} _{\text {knee}}) V. A high current density $ {J}_{\text C}$ of 8 kA/cm2 and power density of 75 kW/cm2 were obtained. These values are the highest in the reported for GaN-based HBTs on sapphire substrates. The open-base breakdown voltage ( ${BV}_{\text {CEO}}$ ) exceeds 98 V comparable with direct-growth GaN-based HBTs.

Extraction and Analysis of Gamma Irradiated Si BJT SPICE Model

The Simulation Program with Integrated Circuit Emphasis (SPICE) model parameters of pre and post-irradiated silicon bipolar junction transistor (Si BJT) were extracted with the use of Altium Designer (AD)/SPICE model wizard. The percentage changes (Δ%) between forward and reverse-bias parameters of existing BJT (ZETEX BCW72) SPICE model were estimated and also the degradation Δ% between the experimental data of pre and post-irradiated Si BJT were calculated. Then the new measured results by comparison were imported into AD/SPICE model wizard to extracts forward-bias parameters. The extracted forward-bias parameters were used to generate reverse-bias parameters through Δ%. The final extracted Si BJT SPICE model parameters were implemented in SPICE simulator to obtained forward and reverse Gummel plots. As expected, base current (IB) increases, the collector current (IC) increases slightly at low bias base-emitter voltage, leading to current gain degradation due to positive charge trapped in the oxide and interface of the BJT device. In addition, the results of the IB in the forward Gummel flows in parallel with base-emitter junction, while the IB in the reverse Gummel flows across the base-collector junction down to the back side collector contact through the collector region. Finally, the compared results of Si BJT forward Gummel simulation and experimental data showed good agreement.

Reliability of high-speed SiGe:C HBT under electrical stress close to the SOA limit

The reliability of high-speed SiGe:C HBT under electrical stress close to the Safe Operating Area (SOA) limit is analyzed and modeled. A long time stress test, up to 1000h, is performed at bias conditions chosen according to applications targeted for these transistors. During the aging tests, Gummel plots are measured at fixed time to analyze the evolution of base and collector current. At low level injection, we observed an increase of the base current whereas the collector current remains constant for the whole Vbe range and during the 1000h aging time. By means of 2D TCAD simulations, this evolution of base current is attributed to trap activity at the emitter-base junction periphery. Based on TCAD simulation results, we propose an aging law using a differential equation that has been implemented in HiCUM L2 v2.33. This reliability-aware compact model allows designers creating reliability-aware circuit architectures at an early stage of the design procedure, well before real circuits are actually fabricated.

(Invited) Combining SiGe BiCMOS and InP Processing in an on-top of Chip Integration Approach

The research on millimeter-wave circuits is driven by applications such as radar imaging and wideband communications. For some applications SiGe hetero junction bipolar transistors (HBTs) are limited in output power, determined by the physical properties of silicon. For SiGe devices with transit frequencies of 180 GHz a breakdown voltage BVCEO of 2.0 V can be measured. The increase in breakdown voltage means always a decrease in transit frequency. On the other hand, silicon is the leading material of modern semiconductor technology. It offers a high level of integration density and yield. SiGe-HBT device speed has increased to hundreds of gigahertz, however limited in output power compared to III-V semiconductor devices. Thus, merging the qualities of both III-V and Si technology will enable a new class of high-performance ICs.Our approach combines a 3” InP-DHBT transferred-substrate process [1] with a SiGe-BiCMOS process [2]. At first, silicon and InP wafers are processed separately. The silicon wafer runs through the complete production process with front-end and back-end in a 0.25 µm BiCMOS process with a five metal layers aluminum/tungsten back-end using silicon dioxide as interlayer dielectric and an additional tungsten local interconnect. The back-end-process was specially adapted for the following wafer bond process by planarization of the topmost metal (TM2) level. The InP wafer has a semi-completed front-end and one metal level of gold and benzocyclobutene (BCB) as the dielectric. At this stage the front-to-front bond process is performed (see Fig. 1 a). The ground metallization (Gd) of the InP wafer is embedded in BCB to achieve a surface step height of less than 100 nm. Prior to wafer bonding both wafers are spin coated with BCB. After a BCB curing process the two wafers are aligned and bonded. After the bond process the InP substrate is etched by HCl to expose the InP-DHBT structures (see Fig. 1 a). The vias between the InP and SiGe-BiCMOS structures are formed by inductively coupled plasma (ICP) reactive ion etching (RIE) dry etching through the BCB using SF6. Then they are electrically connected using a gold electroplating process (see Fig. 1 b).To demonstrate the capabilities of the heterointegration scheme an integrated signal source at 164 GHz was designed and fabricated [3]. It is an example of the different combinations of BiCMOS and InP circuit building blocks. It is shown in Fig. 2. The source consists of a fundamental voltage-controlled oscillator (VCO) in BiCMOS technology (left side in Fig. 2) which is interconnected by an optimized high frequency via transition to a doubler-amplifier combination in InP technology (right side of Fig. 2).Recently, the influences of the wafer bonding and the finalization of the InP-DHBT process on SiGe devices were investigated. It was found that the impact on the BiCMOS devices is rather small. The forward Gummel plot of a SiGe-HBT before and after hetero integration is shown in Fig. 3. There is a slight increase of the base current at low emitter-base voltages caused by leakage currents due to electrostatic discharges in etching processes in the post bonding procedure. But these changes are marginal. Nevertheless, options to remove these effects are being discussed, such as moderate anneal sequences (the post-fabrication temperature is limited to below 250°C due to the presence of BCB) and modifications to the post-waferbonding plasma etch recipes.

Failure Model Research of Power HBTs

Heterojunction bipolar transistors (HBTs) are playing an important role in microwave and power applications. When HBTs operated at high power, the power dissipation and self-heating effects will enable the generation of electrical properties in the transistor failure. The failure experiment system of microwave power HBTs was established. Based on this system, the changes of electrical parameters of HBTs in deferent stress, such as Gummel plots, base current various different base-emitter voltage and base-collector voltage, were measured and analyzed. At the same time, the failure of base current of SiGe HBTs under the condition of FC, SC and thermal stress are studied respectively. It was found that ΔIBis the sensitive parameter of electrical and thermal stress. Based on this reason, we presented the failure model of IB. This model could explain the experiment phenomenon successfully, which is very important and useful for applications of microwave power analog IC’s.

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.

Low temperature performance of pure ternary InAlAs-InGaAs-InAlAs double heterojunction bipolar microwave transistors

All ternary InAlAs-InGaAs-InAlAs Double Heterojunction Bipolar Transistors (DHBTs) are experimentally demonstrated to operate down to liquid nitrogen temperature with a breakdown (BVceo) voltage of 7.6 V at 0.05 kA/cm2 which is achieved despite collector thickness of only 2000 Å and heavy dipole doping of 4 × 1018 cm−3. The wafers were Molecular Beam Epitaxy grown without resorting to any complex growth techniques such as CHIRP (coherent heterointerfaces for reflection and penetration) superlattice or quaternary alloys for grading. Gummel plot shows a finite current gain varying from 4 to 30, as collector current was varied over six orders of magnitude (from 7 nA to 7 mA), and up to a current density of 50 kA/cm2 at 77 K. The resulted high breakdown voltage and relatively better current gain stability over temperature in comparison with SiGe make these microwave devices of relaxed geometry (1 × 15) µm2, fabricated using simple optical lithography which are suitable for many low temperature applications such as high-sensitivity cooled sensors and detectors and cryogenic low-noise amplifiers (LNAs) offering a competitive alternative to deep-submicron SiGe technology.

Performance Characterization of Heterojunction Bipolar Transistor as an Optoelectronic Mixer

This paper explains the development of physical model Heterojunction Bipolar Transistor (HBT) andcharacterizes its performance as an optoelectronic mixer (OEM). HBT has been identified as a suitabledevice to be implemented in optoelectronic mixers by simultaneously photodetecting an intensitymodulated laser beam at 1550nm and frequency translating the detected signal to a higher or lowerfrequency which can provide high mixing efficiency and required condition for an oscillator. The HBTOEM was designed, modeled and simulated by using APSYS Crosslight software. Data from thesimulation such as the gummel plot, energy band diagram and other characteristics have been generatedand analyzed. The device was analyzed considering 1550nm wavelength with up to 30GHz modulatingsignal frequency. Hence, the designed HBT is found to be possible for the implementation of thebroadband RoF system as it can perform the photodetection, amplification and frequency conversionsimultaneously as required at RoF remote antenna unit..

Investigation of Current Gain Degradation in 4H-SiC Power BJTs

The current gain degradation of 4H-SiC BJTs with no significant drift of the on-resistance is investigated. Electrical stress on devices with different emitter widths suggests that the device design can influence the degradation behavior. Analysis of the base current extrapolated from the Gummel plot indicates that the reduction of the carrier lifetime in the base region could be the cause for the degradation of the gain. However, analysis of the base current of the base-emitter diode shows that the degradation of the passivation layer could also influence the reduction of the current gain.

Current Transport Characteristics of Quasi-AlxGa1-xN/SiC Heterojunction Bipolar Transistors with Various Band Discontinuities

The current transport characteristics of quasi-AlxGa1-xN/SiC heterojunction bipolar transistors (HBTs) with various band discontinuities were investigated in a low-current range using a Gummel plot. In the low-current range, the base currents of the HBTs were dominated by recombination currents. The collector current characteristics of the HBTs in the low-current range were almost the same in spite of the various band discontinuities, and the ideality factor n was 1.0. The band discontinuities at the heterojunction had no effect on electron injection in the low-current range. This is because the collector currents were dominated by diffusion process in the base region rather than by injection process at the AlGaN/SiC interface.

$\hbox{InGaP/GaAs}_{0.57}\hbox{P}_{0.28} \hbox{Sb}_{0.15}/\hbox{GaAs}$ Double HBT With Weakly Type-II Base/Collector Junction

We report on the dc characteristics of an InGaP/ GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.57</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.28</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> /GaAs double heterojunction bipolar transistor (DHBT). In comparison with control InGaP/GaAs single heterojunction bipolar transistors (SHBTs), the DHBT shows a lower turn-on voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE, on</sub> ) by ~ 70 mV, a lower knee voltage up to J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ~ 40 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and less temperature-sensitive current gain. The validity of reciprocity in the Gummel plot suggests no potential spikes at the emitter/base and base/collector (BC) junctions of the DHBT. By considering the differences, in terms of the built-in voltage of the BC junction, the Fermi level in the base, and the renormalized energy gap of the base, between the GaAsPSb DHBT and the control InGaP/GaAs SHBT, we conclude that the heavily p-doped GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.57</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.28</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> base and the lightly n-doped GaAs collector are in weakly type-II band alignment with a conduction and valence band offset of 44 and 221 meV, respectively. These findings indicate that GaAsPSb is a promising base material for DHBTs operating at high temperature and low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE, on</sub> conditions without suffering from the collector current blocking.

Electrical behavior research of silicon-on-insulator SiGe heterojunction bipolar transistor

The paper deals with the design optimization of SiGe heterojunction bipolar transistor (HBT) on thin film silicon-on-insulator (SOI). The basic DC and AC current characteristics are obtained and the differences between the SOI and bulk SiGe HBT are analyzed. As the incorporation of SOI substrate makes the SOI SiGe HBT a four-terminal device, the influences of the substrate bias on Gummel plot, output current and avalanche current are studied emphatically. Finally, the physical parameters of material and geometric parameters of the device are discussed by changing the frequency characteristics. Compared with the bulk counterpart, the SOI SiGe HBT is designed and fabricated with a great degree of freedom for better performance. This systematic analysis of SOI SiGe HBT provides a valuable reference for the SOI SiGe BiCMOS circuit design and simulation.

AlGaN/GaN heterojunction bipolar transistors by ammonia molecular beam epitaxy

AbstractWe demonstrate AlGaN/GaN heterojunction bipolar transistors (HBTs) by ammonia molecular beam epitaxy (NH3 MBE). The several benefits offered by NH3 MBE for the growth of GaN based vertical electronic devices are discussed. To obtain good ohmic contacts to the base layer, devices were fabricated with two different processes involving regrowths – regrown base contact (Wafer A) and regrown emitter (Wafer B). Devices on Wafers A and B had similar DC performance. Common emitter (CE) operation with a peak collector current density, JC &gt; 1 kA/cm2 was obtained from devices on both wafers. In CE operation, a current gain (β) of 1.5–3 is observed in devices on both wafers. High base resistance is found to limit the current gain in CE operation, by limiting the base‐emitter bias voltage in the active region of the device. Maximum β values observed from Gummel plots at a fixed base‐collector (BC) bias of zero volts, are β ∼ 15 at JC = 0.88 kA/cm2 for Wafer A and β ∼13.5 at JC = 3 kA/cm2 for Wafer B. In devices on both wafers, variation is observed in the plots of β versus IC (collector current) for devices with the same emitter dimensions and geometry but with different lateral spacing between emitter mesa and base contacts (WEB). Peak β obtained is also observed to vary with WEB. An explanation is provided for the observed behaviour. This work demonstrates the potential of NH3 MBE for the growth of GaN HBTs.

Investigation of optically generated kink effect in GaAs-based heterojunction phototransistors

An optically generated kink observed in the Gummel plot of AlGaAs/GaAs single heterojunction phototransistors (sHPTs) is reported when illuminated with relatively high optical powers. The observed sudden rise in collector current and decrease in the base current, referred to as `optical kink effect', is carefully studied and analyzed. The measurements are performed for incident optical power of up to 225 μW at an incident wavelength of 635 nm. This rise in the current gain of HPTs, in three terminal configuration, is associated with the base-collector space-charge modulation similar to the kirk effect.

Effects of proton irradiation on SiGe HBTs implemented with isolation guard rings

The effects of proton irradiation on SiGe HBTs implemented with isolation guard rings are investigated in this work. Different from what was shown in any of the previous radiation tolerance studies, a distinctive increase of the emitter current after proton irradiation was observed on a measured inverse-mode Gummel plot from the SiGe HBTs implemented with isolation guard rings. Detailed device measurements and modeling revealed a new SiGe HBT degradation mechanism under proton irradiation. It is found that the increase of the emitter current measured in the inverse-mode Gummel plot comes from the degradation of the substrate–collector (buried layer) junction diode associated with the SiGe HBTs. Furthermore, we identified that the radiation damages in the substrate–collector junction near the deep trench edges are solely responsible for the observed degradation of radiation tolerance. The potential impact of this radiation damage to device operation is discussed.

Preliminary results of storage accelerated aging test on InP/InGaAs DHBT

We report on the reliability of InP HBT technology which has applications in very high-speed ICs. This work presents the storage accelerated aging tests results performed on InP/InGaAs HBT at stress temperatures of 180, 210 and 240 °C up to 3000 h. We have performed aging tests for two generations of InP HBT which differ from the collector doping level and from material used for planarization. From the Gummel plots, we note that the major degradation mechanism is located at the base–emitter junction periphery. Investigations on the physical origin of the observed failure mechanism has been performed using TCAD simulations.

Characteristics degradation of the SiGe HBT under electromagnetic field stress

This paper describes a new reliability study in SiGe Heterojunction Bipolar Transistors (HBTs) by which the electromagnetic field aggression effects can be identified. Base current deviation mechanism with current gain degradation is studied for the first time. Reverse Gummel plots and capacitance characterizations indicate that the electromagnetic field stress induces traps not only at the emitter–base spacer’s oxide, but also at the collector–base spacer’s oxide. These traps induce generation/recombination centers, and leads to excess non-ideal base currents. Two-dimensional physical simulations have been used to analyse the impact of this degradation mechanism on the device behavior. As a consequence of introducing surface recombination centers at emitter–base and collector–base spacer’s oxide, a non-ideal base current rises up in agreement with the experimental data extracted. As the density of interface traps increases, the charge contributed by these interface states causes a broadening in the base current response and the capacitances deviation.

Temperature studies of InAlAs–InGaAs–InAlAs double heterojunction bipolar transistors with no current blocking

In this paper, elimination of current blocking for the temperature range 77 K to 400 K is experimentally demonstrated for all ternary InAlAs–InGaAs–InAlAs double heterojunction bipolar transistors of emitter area 100 × 100 µm2. The wafers were grown by molecular beam epitaxy without using any complex growth techniques such as coherent heterointerfaces for reflection and penetration superlattice or quaternary alloys for grading. A room temperature breakdown (BVceo) of 5 V is achieved despite the collector thickness of less than 2000 Å and heavy dipole doping of 4 × 1018 cm−3. Activation energies calculated from the Gummel plots indicate the shift of the transport mechanism across the junction from thermionic emission to predominantly tunneling as the temperature is lowered to 77 K.

$\hbox{In}_{0.46}\hbox{Ga}_{0.54}\hbox{P}_{0.98} \hbox{Sb}_{0.02}/\hbox{GaAs}$: Its Band Offset and Application to Heterojunction Bipolar Transistor

We report on the band alignment of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.46</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.54</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.98</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.02</sub> /GaAs and the dc characteristics of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.46</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.54</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.98</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.02</sub> /GaAs heterojunction bipolar transistors (HBTs). By comparing the forward and reverse Gummel plot, we found a potential spike existing at the InGaPSb/GaAs interface. Through a flatband extrapolation from the currents of the forward and reverse Gummel plot and the energy gap determined from photoluminescence, we concluded that In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.46</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.54</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.98</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.02</sub> /GaAs is in a type-I band alignment. The conduction-band offset and valence-band offset are 0.12 and 0.35 eV, respectively. As a result of the type-I band alignment, the InGaPSb/GaAs HBTs showed a more significant thermal degradation of the current gain than the control InGaP/GaAs HBT. The thermal behavior is beneficial to ruggedness.