GaAs Heterojunction Bipolar Transistor Research Articles

Annealing study of InGaP/GaAs heterojunction bipolar transistor and carbon-doped p +GaAs base layers

In this work we have examined the effect of RF annealing (450–750°C, 5–30 min) upon both InGaP/GaAs-based hetero-junction bipolar transistor (HBT) structures, fabricated by metalorganic vapour phase epitaxy (MOVPE), as well as thick carbon (C)-doped p +GaAs HBT base layers with varying layer thickness, dopant level and type (intrinsic and extrinsic C precursors) and co-doping (In) strain compensation. Anneal-induced changes in the p +GaAs layer lattice strain, Hall carrier concentration and mobility were compared with non-radiative losses, determined from photoluminescence (PL) intensity data. Majority and minority carrier property differences were also compared with IR reflection, Raman backscattering and photoreflectance (PR) data and correlated with changes in MOVPE hydrogen background concentration as determined by secondary-ion-mass-spectroscopy (SIMS). Thick base layer (1.3 μm) HBT structures were also examined for different anneal temperatures and time, showing significant changes in the PR emitter(InGaP)/base (p +GaAs) and base/collector (n-GaAs) interface regions for the 650°C anneal condition, as correlated with both PL and SIMS hydrogen concentration data.

Low turn-on voltage GaAs heterojunction bipolar transistors with a pseudomorphic GaAsSb base

We have developed GaAs heterojunction bipolar transistors (HBTs) with low turn-on voltage by using pseudomorphic GaAsSb as the base layer. The turn-on voltage of GaAs/GaAs0.91Sb0.09 HBT is 0.10 V lower than that of InGaP/GaAs HBT. The lower turn-on voltage is attributed to the smaller band gap of the GaAsSb base layer, indicating that GaAsSb is useful material for reducing turn-on voltage of GaAs HBTs. The current gain of 20 is obtained for GaAs/GaAs0.91Sb0.09 HBT, which is larger than those of previously reported GaAs/GaAsSb HBTs owing to the pseudomorphic, fully strained GaAsSb with no misfit dislocations. The knee voltage of 0.47 V is attained at the collector current density of 5×104 A/cm2. These results indicate that GaAs/GaAsSb HBTs have a great potential for reducing operating voltage and power dissipation.

Electrical performance improvements on RFICs using bump chip carrier packages as compared to standard thin shrink small outline packages

The electrical models of bump chip carrier (BCC) packages have been established based on the S-parameter measurement. When compared to the standard thin shrink small outline packages (TSSOPs), BCC packages show much smaller parasitics in the equivalent model. In the simulation, the insertion and return losses for a packaged 50-/spl Omega/ microstrip line are calculated against frequency. BCC packages are also less lossy than TSSOPs over a wide frequency range. By setting a random variable with Gaussian distribution varied within a certain range for each equivalent circuit element of the packages, the Monte Carlo analysis has been performed to study the package effects on a GaAs heterojunction bipolar transistor (HBT). Again, BCC packages cause less decrement of HBT unity-gain bandwidth than TSSOPs.

A comparison of the effects of gamma irradiation on SiGe HBT and GaAs HBT technologies

A comparison of the effects of gamma irradiation on silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) and gallium-arsenide (GaAs) HBT technologies is reported, DC and radiofrequency (RF) performance as well as the low frequency noise are investigated for gamma doses up to 1 Mrad(Si). The results indicate that both SiGe and GaAs HBT technologies are tolerant to gamma irradiation.

High-speed ADC systems with HBTs for measuring instrument applications

This paper presents very high-speed Analog-to-Digital Converter (ADC) systems for measuring instrument applications, and also related theoretical results. First we describe the design, testing and performance of ≈1 GS/s 6-bit and 7-bit ADCs using SiGe heterojunction bipolar transistor (SiGe HBT), and a 3 GS/s 6-bit ADC and Track/Hold (T/H) circuit using GaAs heterojunction bipolar transistor (GaAs HBT). We show that SiGe HBTs and GaAs HBTs have technological potential, and that the folding/interpolation architecture is suitable for high-speed ADC systems. Next, we derive three theoretical results aimed at very high-speed, wideband ADC systems. ⋅A folding/interpolation architecture is suitable for very high-speed ADCs implemented with HBTs, and digital error correction is required to improve their AC performance. We show an error correction algorithm, as well as its effectiveness and limitation for high-frequency inputs. ⋅Aperture jitter is crucial in wideband ADC systems, and we have derived very general results about aperture jitter effects of such systems. ⋅A time-interleave ADC system can realize very high-speed ADC system, but timing skews in the system degrade its overall accuracy. We have derived the error power corresponding to timing skews. Finally, we discuss several issues relating to standardizing the specifications of very high-speed ADCs targeted at measuring instrument applications.

Temperature distribution over a GaAs heterojunction bipolar transistor measured by fluorescent microthermal imaging

Fluorescent microthermal imaging (FMI) is used to measure the temperature at the surface of a 2×2 μm2 heterojunction bipolar transistor. The presence of an artifact at the emitter post indicates that accurate temperature measurements are limited to flat surfaces. The FMI measurements obtained for various power dissipations are compared with electrical measurements of the junction temperature. The good agreement between the two techniques suggests that the temperature drop along the emitter post of the device is within a few degrees.

Current induced degradation in GaAs HBT's

A physical model for observed current gain degradation in GaAs heterojunction bipolar transistors (HBT's) is suggested in terms of a parameterized mathematical description of accumulating junction damage. The model and measurement suggest a positive correlation between high initial values of DC current gain and longer time to failure. Statistical analysis of accelerated stress failure data at 10 kA/cm/sup 2/ for InGaP-GaAs HBT's was conducted. The result shows projected median time to failure (MTTF) of more than 10/sup 8/ h at a junction temperature of 100/spl deg/C. The standard deviation is 0.6 and the activation energy is 1.5 eV.

Linearity characteristics of GaAs HBTs and the influence of collector design

The linearity characteristics of GaAs heterojunction bipolar transistors (HBTs) are studied through measurement and analysis. Third-order intermodulation distortion behavior of HBTs is examined on devices with various epilayer designs and at various bias points, loads, and frequencies. Calculations from an analytical model reveal a strong bias and load dependence of third-order intercept point (IP3) on the nonlinearities from transconductance and the voltage dependence of base-collector capacitance. However, a simple model is not able to predict the fine details of IP3 with bias. A large-signal HBT model with an accurate description of the base-collector charge is shown to account for the measured trends. The base-collector charge function accounts for the modulation of base-collector capacitance with current, electron velocity modulation, and the Kirk effect (base pushout) for GaAs-based HBTs. A detailed study of the influence of collector design on linearity is also presented.

High-efficiency power amplifier using dynamic power-supply voltage for CDMA applications

Efficiency and linearity of the microwave power amplifier are critical elements for mobile communication systems. This paper discusses improvements in system efficiency that are obtainable when a DC-DC converter is used to convert available battery voltage to an optimal supply voltage for the output RF amplifier. A boost DC-DC converter with an operating frequency of 10 MHz is demonstrated using GaAs heterojunction bipolar transistors. Advantages of 10 MHz switching frequency and associated loss mechanisms are described. For modulation formats with a time-varying envelope, such as CDMA, the probability of power usage is described. Gains in power efficiency and battery lifetime are calculated. An envelope detector circuit with a fast feedback loop regulator is discussed. Effects of varying supply voltage with respect to distortion are examined along with methods to increase system linearity.

Linear high-efficiency microwave power amplifiers using bandpass delta-sigma modulators

A novel amplifier configuration is described, in which a bandpass delta-sigma modulator is used to produce a two-level (digital) signal representing an analog radio frequency (RF) input. Subsequently, a switching-mode amplifier and bandpass filter are used to amplify the signal and remove unwanted spectral components. This configuration has the potential of achieving high efficiency (typical of switching mode amplifiers) together with high linearity. A simulated implementation with GaAs heterojunction bipolar transistors (HBT) is shown.

Failure mechanism and SPICE modeling of [formula omitted] HBT long-term current instability

The long-term current instability of AlGaAs GaAs heterojunction bipolar transistor (HBT) is studied, and the physical mechanism contributing to such a behavior is investigated. Based on this, a model capable of predicting the HBT long-term current drift and mean time to failure (MTTF) is developed. In addition, such a model is implemented into SPICE circuit simulator, thus allowing the simulation of HBT circuits subjected to an electrical and thermal stress condition.

An actively balanced GaAs HBT-Schottky mixer for 3-V wireless applications

Here we present a novel low-voltage active mixer topology which enables 3-V double-balanced active mixer operation from wide-bandgap GaAs-based heterojunction bipolar transistors (HBTs). The compact mixer design integrates directly coupled active radio frequency (RF) and local oscillator (LO) transformer baluns with a Schottky-diode ring-quad to form a double-balanced mixer which operates from DC to 5 GHz. Biased with a low 3-V supply and operated as a down-converter with a fixed LO at 800 MHz and 0 dBm, the mixer achieves 9.4-dB conversion gain (CG) at 1 GHz with positive CG out to 4 GHz and an IP3 of -5 dBm. The LO-IF isolation is >20 dB while the 2-2 spur suppression is >20 dB over a broad 1-5 GHz RF input band. The novel 2.1/spl middot/V/sub BE/ supply design topology allows 3-V operation from the high turn-on voltage GaAs HBT's, making them suitable for portable wireless applications, and can enable 1.5-V operation for Si, Si-Ge, and InP BJT/HBT technologies.

Small-signal distributed model for GaAs HBT's and S-parameter prediction at millimeter-wave frequencies

The development of a new Heterojunction Bipolar Transistor (HBT) distributed electrical model suitable for millimeter-wave applications is reported. Each section of the distributed model is composed of an active slice, modeled as an intrinsic HBT, and connected to other slices through a passive connecting network. It is shown that, for large size and high power HBT's, a distributed model is more accurate than a lumped-element one. This is confirmed by comparing the S-parameters calculated using both models to the measured data over a wide frequency band. It is also shown that the distributed model allows accurate prediction of S-parameter behavior at higher frequencies where the lumped model may not have accurate prediction.

An 18-22-GHz down-converter based on GaAs/AlGaAs HBT-Schottky diode integrated technology

Here we report on a K-band AlGaAs/GaAs HBT-Schottky diode down-converter which represents the highest complexity monolithic integrated GaAs HBT-Schottky MMIC so far demonstrated at K-band frequencies. The MMIC integrates a double-balanced Schottky diode mixer with an 18-22 GHz two-stage K-band radio frequency (RF) amplifier, a 6-10 GHz two-stage X-band IF amplifier, and a 12-GHz local oscillator (LO) heterojunction bipolar transistor (HBT) buffer amplifier. The Schottky diodes are constructed from the existing GaAs HBT base and collector vertical epitaxy layers and can be easily fabricated with only one additional mask processing step. The double-balanced Schottky mixer provides high IP3 and high 2-2 spur suppression over a broad band while consuming little dc power. The HBT-Schottky integrated down-converter MMIC achieves >16-dB conversion gain over an RF input band from 18-22 GHz and a corresponding IP3>10 dBm with only +3 dBm of LO drive. The total chip is 3.85/spl times/3.75 mm/sup 2/ and can be self-biased through a single 5.5-V supply while consuming 545 mW of dc power. The use of GaAs HBT vertical-Schottky-diode technology has inherent performance advantages for frequency conversion MMIC's.

Evaluation of III–V multilayer transport parameters using quantitative mobility spectrum analysis

In this paper we illustrate the power and utility of quantitative mobility spectrum analysis (QMSA) of magnetic field dependent Hall data in order to evaluate the transport parameters of multilayer III–V materials and device structures such as high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs). As a first example, we present the QMSA of a n +GaAs/GaAs/n +AlGaAs/p +GaAs/n GaAs/n +GaAs HBT structure, in which QMSA resolves two carrier species: holes with mobility of 700 cm 2 V −1 s −1 and density 1.6 × 10 18 cm −3, and electrons with mobility of 1530 cm 2 V −1 s −1 and density 3.0 × 10 18 cm −3. A direct comparison with the results of C-V electrochemical profiling indicates that all n +-type layers (sub-collector, emitter and cap) are characterised by an electron mobility which appears in the mobility spectrum as a single peak with an average density corresponding to the sum of all three n + layers. The peak in the hole spectrum may be clearly identified with the single p-type base layer. The second example is an n −1GaAs/n +AlGaAs/AlGaAs/GaAs HEMT structure in which the 2D electron gas population with a mobility of 7750 cm 2 V −1 s −1 and sheet density of 2.6 × 10 11 cm −2 is readily identified and separated from the mobility spectrum peak corresponding to the two highly-doped n-type capping layers. Due to the similar carrier mobility in both capping layers, their contribution to the spectrum appears as a single electron peak at 1100 cm 2 V −1 s −1 with a density of 2.1 × 10 16 cm −3.

A GaAs HBT 16×16 10-Gb/s/channel crosspoint switch

A 16/spl times/16 crosspoint switch IC has been designed and implemented in a 2-/spl mu/m GaAs heterojunction bipolar transistor (HBT) technology. The IC is a strictly nonblocking switch with broadcast capability and asynchronous data paths. The IC has fully differential internal circuitry and is packaged in a custom high-speed assembly. Test results confirmed that the IC achieves a 10-Gb/s/channel (or 160-Gb/s aggregate) capacity, the highest reported to date for a 16/spl times/16 crosspoint switch IC.

Bufferless broadcasting: a low power distributed circuit technique for broadcasting 10-Gb/s chip input signals

Bufferless distributed circuit (BDC) broadcasting is proposed as a technique for broadcasting high-speed chip input signals to a series of on-chip destination cells as needed in crosspoint switch, parallel multiplier, distributed amplifier, etc., chip designs. In contrast with conventional techniques that use an on-chip buffer to assist broadcasting, BDC broadcasting offers the advantage of lower signal delay and power dissipation. In an experimental GaAs heterojunction bipolar transistor (HBT) 8/spl times/4 crosspoint switch assembly, BDC broadcasting was found to achieve a 40% power savings with little or no penalty in jitter or bit error rate performance at a 10-Gb/s data rate.

Dose rate and total dose 1/f noise performance of GaAs heterojunction bipolar transistors

GaAs heterojunction bipolar transistor 1/f noise performance is demonstrated to be unaffected by dose rate and total dose. This is believed to be due to shielding provided by the N/sup +/ collector from the GaAs substrate.

The GaAs heterojunction bipolar transistor: an electron device with optical device reliability

GaAs-based heterojunction bipolar transistors (HBTs) are of interest for a wide variety of applications. However, concerns about the long-term stability of the device have recently arisen. This paper describes the physics of HBT degradation under bias stress as similar to GaAs light-emitting diode (LED) and laser diode (LD) degradation. TEM, electroluminescence, and electrical measurements support this model. Additionally, the model also indicates the factors in epitaxial growth and device processing that are critical to device reliability.

Recent progress in the multi-wafer CBE system

Recent progress in the multi-wafer CBE system has demonstrated the potential capability of producing the state-of-the-art compound semiconductor devices with excellent uniformity and reproducibility. The Al compositional uniformity of three 4 inch wafers grown at the same time is 0.2136 ± 0.0014 (standard deviation). The uniformity in thickness, composition, carrier concentration for three 3 inch wafers is within ±1.8%, ±0.003 (Ga in InGaP), and ±2.2%, respectively. The temperature variation across a 3 inch GaAs wafer is ±0.9°C. The extreme abruptness of composition and the doping profiles using gaseous dopant sources are another remarkable advantage of this growth system. The extremely low surface defect density of 2.8 cm −2 for GaAs is routinely obtained. The InGaP GaAs heterojunction bipolar transistor (HBT) with high current gain and superior high-frequency characteristics of excellent uniformity is successfully fabricated. These remarkable results are ascribed to the unique and superior design of the overall growth system: i.e. the novel metalorganic gas cells with the tilted aperture without any diffuser, the improved In-free substrate holder, the completely shut-off shutters, and the gas handling system.