AlGaAs Emitter Research Articles

AlGaAs/GaAs HBTs with C-doped base and undoped emitter-base spacer layer

Effect of undoped GaAs spacer layer between AlGaAs emitter layer and C-doped GaAs base layer on DC characteristics of AlGaAs/GaAs HBTs with ledge structure was investigated. Devices with spacer layer thickness (∼3-5 nm) and optimal ledge geometry demonstrate stable high current gain (βmax = 120-140) combined with collector-emitter breakdown voltage of 23-25V.

Effect of a wideband heteroepitaxial emitter on dynamics of turn-off switching of high-voltage power GaAs p-i-n diodes

The possibility of improving the dynamic characteristics of turn-off switching of high-voltage power GaAs p-i-n diode by applying a heteroepitaxial AlGaAs emitter is investigated in this work. Using a wideband AlGaAs n+-emitter in manufacturing of power GaAs p-i-n diodes allows to vary the coefficient K value which characterizes the recovery softness of diode blocking properties when switching off in the range of 0.1 to 2 or more. The diodes with blocking voltage of up to 700 V, the reverse recovery time of about 40 ns and K > 1 were manufactured.

Photoluminescence investigation of Be-doped Npn AlGaAs/GaAs heterojunction bipolar transistor structures

Highly complex Npn AlGaAs/GaAs single heterojunction bipolar transistor (HBT) layers with Be-doped base were investigated by photoluminescence (PL) spectroscopy. Room temperature PL shows only a broad peak of GaAs due to thermalization; 15 K PL shows five peaks. The peak at ∼1.481 eV is from a p-type GaAs base, that at ∼1.517 eV is from a low-doped GaAs layer and that at ∼1.55 eV is from a high-doped GaAs collector. The that at ∼1.849 eV is due to bound exciton recombination in an AlGaAs emitter, and that at ∼1.828 eV is due to the acceptor-related transition from the AlGaAs layer. The integrated intensity ratio of these two peaks can be used to investigate the Be outdiffusion behavior, thus optimizing the growth conditions of base. The DC current gain of the HBT structure with different growth conditions was found to be in good agreement with the PL results.

Nondestructive determination of beryllium outdiffusion in AlGaAs/GaAs heterojunction bipolar transistor structures by low-temperature photoluminescence

In this work, low-temperature photoluminescence (PL) is used for the investigation of beryllium (Be) dopant outdiffusion in AlGaAs/GaAs single-heterojunction bipolar transistors (HBTs). Near the typical emission peak at ∼1.92 eV which is due to the band-to-band transition from AlGaAs emitter, an additional emission peak is found in the PL spectrum. This peak is found to be caused by the Be-related transition from AlGaAs emitter due to the Be outdiffusion from the GaAs base to the AlGaAs emitter. The concentration of Be outdiffused into the emitter can be estimated from the energy separation between these two emission peaks in AlGaAs range based on the band gap narrowing effect. The measured dc current gain and the emitter-base turn-on voltage of the HBTs fabricated on different wafers with different growth conditions were found to correlate well with the PL results. Our results demonstrate that low temperature PL technique is an efficient method in identifying Be outdiffusion in HBTs and is useful in HBT growth and device structure optimization.

InGaP HBT technology for RF and microwave instrumentation

An InGaP emitter HBT IC process developed for RF and microwave instrumentation is described. The process is based on MOCVD epitaxial material, 1 μm critical dimension (CD), G-line, stepper aligned lithography and SiCl 4 based reactive ion etching. F t and F max values of 65 and 75 GHz, respectively are achieved. The HBT technology is well suited for instrument applications in that it can simultaneously achieve both excellent reliability and high performance in terms of broad bandwidth, low phase noise, high gain and linearity. Circuits designed in the process include a Darlington feedback amplifier, which achieves 9.8 dB gain from dc to 20 GHz and dc to 16 GHz dividers. The circuits have been utilized in numerous instrument applications and have resulted in improvements in dynamic range, bandwidth and time-domain jitter. Extensive reliability testing of the InGaP emitter process indicates that MTTF values at T j=150°C and J C=6×10 4 A/cm 2 are greater than 4×10 5 h and are an order of magnitude larger than MTTF values for AlGaAs emitter devices.

The simulation of charge transport in the nanostructure “Camel” and heterotransistors

Heterojunction bipolar GaAs transistor with AlGaAs emitter and Si-“Camel”-transistor were simulated using manyparticles method for hot electrons and stochastic dynamics method for equilibrium holes and electrons. Some transient processes were investigated at times of the order 10 −11 s. Dynamics of transient processes is affected by electron space charge and unequipotentiality of base region.

Compositionally graded emitter InGa(As)P/GaAsheterojunction bipolar transistors

The first successful fabrication of compositionally graded emitter InGa(As)P/GaAs HBTs is reported. It is found that the influence of recombination current in the emitter depletion layer on current gain characteristics by compositional grading is small. The recombination current in the InGa(As)P emitter layer is less than 1/10 that in an AlGaAs emitter layer grown at a 100°C higher temperature.

The effect of emitter layer variations on the current gain of AlGaAs-GaAs heterojunction bipolar transistors grown by chemical beam epitaxy

AlGaAs-GaAs heterojunction bipolar transistors have been fabricated with current gains > 200 for devices with emitter dimensions of 2×2 μm 2. The epitaxial layers were grown using chemical beam epitaxy and were npn single heterojunction transistors with aluminum grading in the base. The high current gains observed in these devices are attributed to leaving a thin AlGaAs emitter layer (30–60 nm) over the entire base mesa and alloying through this layer to make base contact. This reduces the surface recombination currents to the extent that no significant decreases of current gain were observed with decreasing emitter size. Values of f t and f max from 50–110 GHz were measured with f max values dependent on the base doping which was in the (2−6) × 10 19 cm -3 range. The epitaxial layers were grown on 3 inch diameter semi-insulating substrates in a VG Semicon 4200 CBE system. Room temperature photoluminescence intensities were used to determine the optimum growth conditions for both the n-Al 0.3Ga 0.7As emitters and the p-Al x Ga 1− x As graded bases. SIMS, DCD X-ray diffraction, Hall effect measurements and photoreflectance were also used to evaluate the grown layers. Variations in emitter composition, doping and thickness were studied as well as the effects of growth interrupts at the emitter-base junction. Digital circuits that operate at data rates above 10 Gb/s> have been demonstrated. These include 4:1 multiplexers, 1:4 demultiplexers, dividers, preamplifiers and decision circuits.

A new emitter design of InGaP/GaAs HBTs for high-frequency applications

An HBT (heterojunction bipolar transistor) structure using an AlGaAs-InGaP emitter is proposed. The AlGaAs-InGaP configuration introduces an electron launcher in the emitter and makes use of the velocity overshoot effect. This enhances the emitter transport and reduces the electron accumulation in the emitter. Simulations show that, by using the AlGaAs-InGaP structure, the emitter charging time can be greatly reduced compared to the conventional AlGaAs emitter design. As a result, the cutoff frequency can be substantially increased. A cutoff frequency of 235 GHz has been predicted. >

Low-temperature migration enhanced epitaxy of base material for AlGaAs/GaAs heterojunction bipolar transistors

Migration enhanced epitaxy (MEE) was used in this work to grow p+-GaAs at the substrate temperature of 300 °C for the base of AlGaAs/GaAs heterojunction bipolar transistors. The results indicated that the low-temperature MEE-grown p+-GaAs epitaxial layers (p=1×1019–1×1020 cm−3) exhibited a crystalline quality comparable to those grown by standard MBE at a substrate temperature of 570 °C. AlGaAs/GaAs HBTs with low-temperature MEE-grown bases doped at p≊2×1019 cm−3 were fabricated by using a self-alignment technique. For the devices with the conventional MBE-grown base, secondary ion mass spectroscopy depth profiles showed a significant Be diffusion into the AlGaAs emitter and as a consequence, the devices showed no current gain. For the devices with the low-temperature MBE-grown base, there was a negligible Be penetration into the emitter and the devices exhibited a common-emitter dc current gain of 13.

Parasitic conduction current in the passivation ledge of AlGaAs/GaAs heterojunction bipolar transistors

Passivating the extrinsic base surfaces of AlGaAs/GaAs heterojunction bipolar transistors with a thin AlGaAs emitter ledge is widely utilized to reduce the extrinsic base surface recombination current. The effect on current gain of this ledge being only partially depleted is analyzed. This analysis examines the ledge parasitic conduction current as a function of device geometry. Results indicate that even with an undepleted portion of the ledge as thin as 50 Å, the elimination of base contact recombination current requires a passivation ledge length 6 times longer than from devices with a fully-depleted passivation ledge. The effect of a base quasi-electric field on the current gain as a function of passivation ledge distance is also discussed. This theoretical analysis is compared with published experimental work.

Growth of carbon-doped base GaAs/AlGaAs HBT by gas-source MBE using TEG, TEA, TMG, AsH 3, and Si 2H 6

High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI 2H 6 ( n = 9 × 10 17 cm -3), and the base layer (92.5 nm) was doped with carbon from TMG ( p = 4 × 10 19 cm -3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 10 4 A/cm 2. The device characteristics of our carbon-doped HBTs were found to be stable under current stress.

Effect of molecular-beam epitaxy growth conditions on GaAs–AlGaAs heterojunction bipolar transistor performance: Beryllium incorporation and device reliability

We have studied the effect of molecular-beam epitaxy (MBE) growth conditions on the performance and reliability of npn GaAs–AlGaAs heterojunction bipolar transistors (HBTs). Wafers grown under normal conditions yield devices with high current gain, but suffer premature failure due to interstitial beryllium diffusion from the base into the graded AlGaAs emitter. Wafers grown with high arsenic/gallium flux ratio and reduced substrate temperature during base deposition have high current gain, and are extremely reliable. Mean time to failure, as defined by a 10% reduction in original current gain, is ≳ 108 h at 125 °C junction temperature for devices grown using conditions optimized for device reliability. We believe the ability to produce high reliability HBTs by MBE is vital to future applications of this technology.

Current gain of graded AlGaAs/GaAs heterojunction bipolar transistors with and without a base quasi-electric field

Graded AlGaAs/GaAs heterojunction bipolar transistors with and without a base quasi-electric field are fabricated to investigate the various components of base current. The experimental results demonstrate that the base current for devices with extrinsic base surface passivation is dominated by base-emitter space-charge recombination current, rather than base bulk recombination current. Both a simple theoretical calculation and SEDAN (semiconductor device analysis) simulations are used to support this finding. SEDAN simulations also indicate strong effects of hole barrier lowering which reduces device current gain when the current gain approaches values of 1000 and when the maximum aluminum composition in the AlGaAs emitter is <or=30%. The experimental finding that space-charge recombination current dominates the base current in passivated graded HBTs agrees well with published theoretical work. This work and other published experimental and theoretical works are compared and discussed.<<ETX>>

Cathodoluminescence study of the damage induced by low-energy boron implantation using a chemical bevel

Boron implantation is used in AlGaAs/GaAs heterojunction bipolar transistor fabrication technology in order to eliminate the lateral diode between the n+-GaAs emitter contact layer and the p+-GaAs implanted well. The cathodoluminescence intensities measured on a bevel before and after the implantation have been investigated to evaluate the amount of damage induced by low-energy implantation in the underlying AlGaAs emitter layer.

Uniform, high-gain AlGaAs/In/sub 0.05/Ga/sub 0.95/As/GaAs P-n-p heterojunction bipolar transistors by dual selective etch process

AlGaAs/InGaAs/GaAs P-n-p heterojunction bipolar transistors (HBTs) have been fabricated using a dual selective etch process. In this process, a thin AlGaAs surface passivation layer surrounding the emitter is defined by selective etching of the GaAs cap layer. The InGaAs base is then exposed by selective etching of the AlGaAs emitter. The resulting devices were very uniform, with current gain varying by less than +or-10% for a given device size. Current gain at a given emitter current density was independent of device size, with gains of over 200 obtained at current densities above 5*10/sup 4/ A/cm/sup 2/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Emitter size effect on current gain in fully self-aligned AlGaAs/GaAs HBT's with AlGaAs surface passivation layer

The emitter size effect for fully self-aligned AlGaAs-GaAs heterojunction bipolar transistors (HBTs) with depleted AlGaAs passivation layers, in which the partially thinned AlGaAs emitter is self-aligned by using the dual sidewall process, is investigated. It is demonstrated that drastic improvement in the emitter size effect can be achieved with an AlGaAs passivation layer as small as 0.2 mu m in width, due to the surface recombination current reduction by a factor of 1/40 in the extrinsic base region. It has also been found that the base current is dominated by excess leakage current in the proton-implanted isolation region.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Residual damage after annealing of Be and O implanted GaAs/AlGaAs hetero bipolar transistors

Beryllium (2.5·1014/cm2 at 40 keV and 7.5·1014/cm2 at 90 keV) and oxygen (1013/cm2 at 380 keV) were implanted into a GaAs/AlGaAs-HBT (hetero bipolar transistor) to facilitate the formation of an ohmic contact with the p-type base using planar technology. The layer sequence and doping levels of the HBT are listed in table 1. Annealing was performed using optical RTA (rapid thermal anneal) equipment, at 860 °C, for 3 s. Technological data as well as SIMS, electrical, and photoluminescence measurements are published in detail elsewhere. This paper focuses on the residual lattice damage in the annealed HBT. TEM investigations were performed at 200 keV beam voltage using cross-sectional specimens.Fig.l shows a dark-field micrograph taken with a {200} reflection. The different layers are numbered (cf. table 1) and can be distinguished by differences in overall contrast. The residual damage consists of Frank type (b=a/3&lt;111&gt;) and perfect(b=a/2&lt;110&gt;) dislocation loops. The perfect loops are prismatic. Most of them lie in the &lt;110&gt; plane perpendicular to the Burgers vector b. All loops are of interstitial type. Defects are only found in the top three layers of the HBT which corresponds to the depth of the Be implantation. The defect distribution is inhomogeneous (Fig.1): While there are rather large loops (up to 200 nm) together with small ones in the GaAs layers of cap and base, only small loops (up to 30 nm) can be observed in the AlGaAs emitter layer.

Carbon-doped base GaAs-AlGaAs HBT's grown by MOMBE and MOCVD regrowth

High-quality GaAs-AlGaAs heterojunction bipolar transistors (HBTs) in which the carbon-doped base layers (p=10/sup 10/-10/sup 20/ cm/sup -3/, 400-800 AA thick) and Sn-doped collector and subcollector layers are grown by metalorganic molecular-beam epitaxy (MOMBE) and a subsequent regrowth using metalorganic chemical vapor deposition (MOCVD) is used to provide the n/sup +/ AlGaAs emitter and GaAs/InGaAs contact layers are discussed. A current gain of 20 was obtained for a base doping of 10/sup 19/ cm/sup -3/ (800 AA thick) in a 90- mu m-diameter device, with ideality factors of 1.0 and 1.4 for the base-collector and emitter-base junctions, respectively, demonstrating the excellent regrowth-interface quality. For a base doping of 10/sup 20/ cm/sup -3/ (400 AA thick), the current gain decreased to 8.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Planar AlGaAs/GaAs HBT fabricated by MOCVD overgrowth with a grown base

A planar heterojunction bipolar transistor (HBT) with an AlGaAs emitter layer epitaxially grown onto a selectively defined grown base layer, where the base is grown with the collector as part of the original epi, is discussed. The transistors fabricated with this process exhibit good gain and output characteristics. Transistors with 7*7 mu m/sup 2/ emitters have exhibited a DC current gain of 10 to 1000 for base doping from 1*10/sup 19/ to 8*10/sup 17/ cm/sup 3/, respectively, and Early voltages >or=100 V. The propagation delay of 19-stage ring oscillators was 87 ps/gate. The transistor-fabrication process was designed to be manufacturable, and the planar nature of the transistor surface should permit large-scale integration with good yields.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>