Performance Of Heterojunction Bipolar Transistors Research Articles

TEM study of phosphorus-implanted pseudomorphic Si0.88Ge0.12 on Si(100)

SiGe is being extensively investigated for use in heterojunction bipolar-transistors (HBT) and high-speed integrated circuits. The material offers adjustable bandgaps, improved carrier mobilities over Si homostructures, and compatibility with Si-based integrated-circuit manufacturing. SiGe HBT performance can be improved by increasing the base-doping or by widening the base link-region by ion implantation. A problem that arises however is that implantation can enhance strain-relaxation of SiGe/Si.Furthermore, once misfit or threading dislocations result, the defects can give rise to recombination-generation in depletion regions of semiconductor devices. It is of relevance therefore to study the damage and anneal behavior of implanted SiGe layers. The present study investigates the microstructural behavior of phosphorus implanted pseudomorphic metastable Si0.88Ge0.12 films on silicon, exposed to various anneals.Metastable pseudomorphic Si0.88Ge0.12 films were grown ~265 nm thick on a silicon wafer by molecular-beam epitaxy. Pieces of this wafer were then implanted at room temperature with 100 keV phosphorus ions to a dose of 1.5×1015 cm-2.

Germanium content dependence of radiation damage in strained Si/sub 1-x/Ge/sub x/ epitaxial devices

The irradiation damage in n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x/ epitaxial diodes and n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x//n-Si epitaxial heterojunction bipolar transistors (HBTs) by fast neutrons and MeV electrons is studied as a function of fluence and germanium content for the first time. The degradation of the electrical performance of both diodes and HBTs by irradiation increases with increasing fluence, while it decreases with increasing germanium content. The damage coefficient of reverse current for x=0.12 and 0.16 diodes irradiated by neutrons is calculated to be 6.2/spl times/10/sup -21/ and 5.5/spl times/10/sup -21/ n/sup -1/ A cm/sup 2/, respectively. That of h/sub FE/ for electron-irradiated x=0.08, 0.12 and 0.16 HBTs is 7.6/spl times/10/sup -16/, 2.7/spl times/10/sup -16/ and 1.6/spl times/10/sup -16/ s/sup -1/ cm/sup 2/ respectively. >

Fourier Analysis-Based Method for High-Frequency Performance Calculation of Heterojunction Bipolar Transistor

A method to evaluate high-frequency performance of heterojunction bipolar transistors based on Fourier analysis of the non-stationary collector current response is proposed. The nonequilibrium electron transport and velocity overshoot effects are taken into account by ensemble Monte Carlo particle simulation. The influence of the emitter and collector capacitances on the high-frequency performance are also included in our consideration. It is found that the conventional method for cut off frequency calculation underestimates its value. Experimental results reported in the literature are compared with the results of numerical simulation. The comparison shows high accuracy and validity of the developed method.

High frequency performance of SiC heterojunction bipolar transistors

A compact heterojunction bipolar transistor (HBT) model was employed to simulate the high frequency and high power performances of SiC-based bipolar transistors. Potential 6H-SiC/3C-SiC heterojunction bipolar transistors (6H/3C-HBT's) at case temperatures of 27/spl deg/C (300 K) through 600/spl deg/C (873 K) were investigated. The high frequency and high power performance was compared to AlGaAs/GaAs HBT's. As expected, the ohmic contact resistance limits the high frequency performance of the SiC HBT. At the present time, it is only possible to reliably produce 1/spl times/10/sup -4/ /spl Omega/-cm/sup 2/ contact resistances on SiC, so an f/sub T/ of 4.4 GHz and an f/sub max/ of 3.2 GHz are the highest realistic values. However, assuming an incredibly low 1/spl times/10/sup -6/ /spl Omega/-cm/sup 2/ contact resistance for the emitter, base, and collector terminals, an f/sub T/ of 31.1 GHz and an f/sub max/ of 12.7 GHz can be obtained for a 6H/3C-SiC HBT. >

Self-aligned InAlAs/InGaAs heterojunction bipolar transistor with a buried subcollector grown by selective epitaxy

We report the first microwave characterization of an In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistor (HBT) with a buried InGaAs subcollector grown by selective epitaxy. The study compares two HBT's having identical 2/spl times/10 /spl mu/m/sup 2/ self-aligned emitter fingers but different subcollectors. Improvement in microwave performance of the selectively-grown HBT over the conventional HBT was observed due to the reduced parasitic base-collector capacitance achieved by incorporating the selectively-grown buried subcollector. >

An introduction to GaAs/GaAlAs HBTs for power applications

Abstract This paper presents a brief introduction to GaAs/GaAlAs heterojunction bipolar transistors (HBTs) for microwave and millimetre-wave power applications. The theoretical advantages of the heterojunction are outlined and the benefits of its incorporation in DC, RF and power devices are discussed. The problems inherent in the realization of HBTs in terms of device design, epitaxial material growth and device fabrication are discussed and the performance characteristics for practical devices presented. The paper concludes with a look at state-of-the-art GaAs/GaAlAs HBT performance and its standing with respect to the competing technologies of the metal semiconductor field effect transistor (MESFET) and the high electron mobility transistor (HEMT).

Avalanche breakdown effects on AlGaAs/GaAs HBT performance

The performance of heterojunction bipolar transistors operating in the avalanche breakdown regime has been evaluated. The analysis shows that AlGaAs/GaAs HBT under avalanche breakdown has higher collector-base junction capacitance, lower Early voltage, higher device noise, lower power efficiency, lower cut-off frequency, reduced device switching speed, and degraded maximum frequency of oscillation.

An analytical model for current transport in AlGaAs/GaAs abrupt HBTs with a setback layer

An intrinsic setback layer (or spacer) is frequently used in abrupt heterojunctions to improve the emitter injection efficiency and to reduce the impurity out-diffusion from the heavily doped base to the emitter. We have developed an analytical model to predict the d.c. performance of the AlGaAs/GaAs abrupt heterojunction bipolar transistor (HBT) with a setback layer. The effects of different setback layer thicknesses on the collector and base currents are studied in detail. Our results suggest that the presence of the setback layer can improve injection efficiency, but it can also increase the base current. Furthermore, for the device considered and parameters used, it was shown that a setback layer with a 100 Å thickness can yield the highest current gain and that a setback layer thicker than 100 Å can actually degrade the HBT performance. The model predictions compare favorably with the results obtained from solving numerically the Poisson and continuity equations including the nonuniform spatial band distribution as well as carrier degeneracy.

Comparison of pnp and npn InGaAlAs/InGaAs heterojunction bipolar transistors

The molecular-beam epitaxial growth conditions and characteristics of npn and pnp heterojunction bipolar transistors in the InGaAlAs/InGaAs material system are described. Direct-current current gains of more than 15 000 have been obtained for npn heterojunction bipolar transistors (HBTs). pnp HBTs have a larger breakdown voltage compared to equivalent npn HBTs. A novel pnp HBT structure in which a strained hole filter is placed just above the base to inject light holes preferentially is proposed. The high speed performance of pnp HBTs is at present limited by emitter series resistance.

High/f/sub max/ collector-up AlGaAs/GaAs heterojunction bipolar transistors with a heavily carbon-doped base fabricated using oxygen-ion implantation

AlGaAs/GaAs collector-up heterojunction bipolar transistors (HBTs) with a heavily carbon-doped base layer were fabricated using oxygen-ion implantation and zinc diffusion. The high resistivity of the oxygen-ion-implanted AlGaAs layer in the external emitter region effectively suppressed electron injection from the emitter, allowing collector current densities to reach values above 10/sup 5/ A/cm/sup 2/. For a transistor with a 2- mu m*10- mu m collector, f/sub T/ was 70 GHz and f/sub max/ was as high as 128 GHz. It was demonstrated by on-wafer measurements that the first power performance of collector-up HBTs resulted in a maximum power-added efficiency of as high as 63.4% at 3 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Current gain collapse in microwave multifinger heterojunction bipolar transistors operated at very high power densities

The rapid development of heterojunction bipolar transistor (HBT) technologies has led to the demonstration of high power single-chip microwave amplifiers. Because HBTs are operated at high power densities, the ultimate limits on the performance of HBTs are imposed by thermal considerations. The authors address a thermal phenomenon observed when a multifinger power HBT is operating at high power densities. This phenomenon, referred to as the collapse (of current gain), occurs when suddenly one finger of the HBT draws most of the collector current, leading to an abrupt decrease of current gain. A quantitative model and the condition separating the normal operation region and the collapse are presented. Critical difference of the collapse in the constant l/sub b/ and constant V/sub be/ modes of operation is discussed for the common-emitter l-V characteristics. The collapse in the common-base l-V characteristics and its relationship with avalanche breakdown are also described. A solution to eliminate the collapse is experimentally verified. >

Conversion gain and intermodulation performance of a GaAs HBT 50–950 MHz upconvertor

The Letter reports the measured performance of a single ended GaAs heterojunction bipolar transistor (HBT) upconverting mixer from 50 to 950 MHz, showing a conversion gain of 19.4 dB and output intermodulation intercept point (OIP3) of +20.5 dBm with local oscillator drive power of 0 dBm. The measured results demonstrate the suitability of the HBT for use in low power consumption upconvertor circuits.

Fabrication, Performance, and Reliability of InP-Based HBTs

ABSTRACTOver the past 10 years, heterojunction bipolar transistors (HBTs) have progressed to where integrated circuit (IC) products are being sold and foundry services are being commercially offered utilizing gallium arsenide (GaAs) based technology. We will discuss, here, an alternative HBT technology based on indium phosphide (InP). While this technology is less mature than its GaAs counterpart, it offers several attractive benefits in comparison with GaAs. These benefits are provided through several key material properties of InP and ternary compound semiconductors, eg. gallium indium arsenide (GaInAs), grown on the InP. We review the status of this npn HBT technology and present performance results which illustrate the benefits of the technology with respect to electronic applications. Finally, we present measured reliability data for this technology which shows outstanding projected lifetimes.

Base thickness and high-frequency performance of SiGe HBT's

The influence of the base thickness on the high-frequency performance of about 20 fabricated HBTs (heterojunction bipolar transistors) has been analyzed by plotting the highest obtained f/sub T/ value against base thickness. Base thickness is defined as the distance between the two Si/SiGe interfaces which usually coincide with the metallurgical pn-junctions. A steady increase of f/sub T/ with decreasing base thickness can be clearly seen: starting from the first published HBTs with 50 nm base thickness which did not exceed 20 GHz, transistors with 40 nm base had 37-52 GHz and devices with 28-30 nm bases exhibited 58-91 GHz. The latest two samples had only 25 and 22 nm base thicknesses, leading to an f/sub T/ of 95 GHz (f/sub max/=50 GHz), the highest value reported for Si transistors. The base doping in the latter sample was 8*10/sup 19/ cm/sup -3/ to maintain a base sheet resistance of about 1.2 k Omega .

Quantitative depth profiling resonance ionization mass spectrometry of GaAs/AlGaAs heterojunction bipolar transistors

Resonance ionization mass spectrometry of neutral atoms sputtered from GaAs/AlGaAs materials, used for heterojunction bipolar transistors (HBT), provides quantitative information about the dopant position near interfaces. The results help elucidate beryllium dopant migration because they are free of matrix effects common in secondary ionization mass spectrometry. HBT performance is shown to be associated with Be location. Quantitative analysis of Be is possible across the AlGaAs/GaAs interface without extensive use of standards. The magnitudes of dopant (Be) and matrix (Al) signals are related in proportion to their concentration.

A COMPARISON BETWEEN THE HETEROJUNCTION BIPOLAR TRANSISTOR POWER PERFORMANCE COMPUTED USING LARGE SIGNAL “Y” PARAMETERS AND A FULL TIME DOMAIN SIMULATION

This model is intended to simulate the large signal performance of heterojunction bipolar transistors for use in high power, high frequency, oscillators, amplifiers, and mixers. A temperature model which includes velocity overshoot and carrier energy effects has been developed. The model is used to calculate the large signal “Y” parameters of an HBT. A comparison is made between predicted power performance using the “Y” parameters and a fully numerical, time domain computation. Advantages and disadvantages of each approach are given.

In-based p ohmic contacts to the base layer of AlGaAs/GaAs heterojunction bipolar transistor

A reliable p ohmic contact for AlGaAs/GaAs heterojunction bipolar transistor (HBT) using AuBe-In/Ag/Au is presented. Excellent morphology after annealing at 400 °C for 20 s was observed and a transfer resistance of 0.095 Ω mm obtained on p+-GaAs (1×1019 cm−3). Silver acts as a diffusion barrier to prevent Au spikes which will degrade the performance of the thin base layer HBT. The indium layer is highly desirable to reduce the contact resistance by forming the InGaAs phase at metal-GaAs interfaces. Beryllium is the p-type dopant and a top gold layer is used to lower the sheet resistance of the contact metals. The mode of current transport is dominant by tunneling through the barrier due to field emission in the heavily doped materials.

High frequency AlGaAs/GaAs heterojunction bipolar transistors: the role of MOVPE

The impressive performance of heterojunction bipolar transistors (HBTs) for high speed applications is based upon the use of modern sophisticated epitaxial growth techniques. This paper is concerned with the role of metalorganic vapour phase epitaxy (MOVPE) in HBT research and development. After a short review of state-of-the-art MOVPE grown HBT devices and circuits the basic operation of the HBT and the predicted performance are discussed. Out of many contributions where MOVPE has an impact on HBT quality the following issues are selected: the growth of highly-doped GaAs: Si cap and contact layers, of highly Mg-doped graded base layers with abrupt dopant profiles, and collector layers with breakdown voltages above 15 V. Attention is drawn to photoluminescence as an efficient and fast analysis tool for HBT layer characterization prior to processing. DC and high frequency results of single devices are discussed. Differential current gains of 150 and cut-off frequency fT25 GHz with non-self-aligned processing fo the HBT layers have been achieved. Based upon MOVPE growth additional improvements are proposed, which may lead to an increase of fT50 GHz and of fmax100 GHz. The low defect density in MOVPE layers, typically < 10 defects/cm2 is a prerequisite for high yield. The achievable homogeneity and reproducibility combined with a high throughput allow the prediction that MOVPE grown HBT layers will satisfy the requirements of industrial HBT production.

0.7 W X-Ku-band high-gain, high-efficiency common base power HBT

Small sized AlGaAs-GaAs HBTs (heterojunction bipolar transistors) have achieved excellent power performance throughout the microwave frequency band. With the implementation of the multi-via-hole design, the HBT performance (gain and efficiency) is maintained as the size increases. A 0.7 W common-base (CB) power HBT with performance around 10 dB gain and 50% PAE well into the Ku band is reported. The performance is comparable to the pseudomorphic HEMT in this frequency range. The yield and uniformity are excellent. The high bias voltage (9.3 V V/sub ce/) is also desirable from a system viewpoint. >

Advances in Photoreflectance Analysis of HBT Wafers

ABSTRACTThis Poster describes the work done in a joint effort Research and Development Program with a leading University, with funding from the state, to develop a heterojunction bipolar transistor (HBT) epitaxial wafer screening tool. A computerized characteristics to HBT performance will be described.Photoreflectance data from about twenty HBT wafers that have been grown and have had test transistors fabricated from the wafers will be analyzed to determine the bandgap of the epitaxial materials and the electric fields.Comparison with previous works will be made in an attempt to reach a unified agreement in understanding that may lead to an ASTM test method.