Μm Emitter Research Articles

Microwave operation of high power InGaP/GaAs heterojunction bipolar transistors

The first high power demonstration of an InGaP/GaAs heterojunction bipolar transistor is presented. Multifinger selfaligned HBTs were tested at 3 GHz. A maximum output power of 2.82 W CW was obtained for a 600 μm2 emitter area device (4.7 mW/μm2 power density) with an attendant gain of 6.92 dB; simultaneously, the device exhibited 55.2% power added efficiency, 69.1% collector efficiency and 8.0 × 104 A/cm2 emitter current density.

High-speed InP/InGaAs HBTs operated at submilliampere collector currents

Extremely small-emitter InP/InGaAs heterojunction bipolar transistors have been fabricated by using a selfalignment technique on MOCVD-grown material. Fabricated devices with a 1 × 2 μm2 emitter electrode showed fT exceeding 100GHz at submilliampere collector currents of Ic >0.6mA. A maximum fT of 163GHz at Ic = 2.3mA ranks with the fT = 176GHz achieved by a simultaneously fabricated 2 × 20 μm2 transistor at Ic = 45mA.

Growth of GaAs/AlGaAs HBTs by MOMBE (CBE)

In this paper, we will discuss how the unique growth chemistry of MOMBE can be used to produce high speed GaAs/AlGaAs heterojunction bipolar transistors (HBTs). The ability to grow heavily doped, well-confined layers with carbon doping from trimethylgallium (TMG) is a significant advantage for this device. However, in addition to high p-type doping, high n-type doping is also required. While elemental Sn can be used to achieve doping levels up to 1.5×10 19 cm -3, severe segregation limits its use to surface contact layers. With tetraethyltin (TESn), however, segregation does not occur and Sn doping can be used throughout the device. Using these sources along with triethylgallium (TEG), trimethylamine alane (TMAA), and AsH 3, we have fabricated Npn devices with 2 μm×10 μm emitter stripes which show gains of ≥ 20 with either ƒ t = 55 GHz and ƒ max = 70 GHz or ƒ t = 70 GHz and ƒ max = 50 GHz, depending upon the structure. These are among the best RF values reported for carbon doped HBTs grown by any method, and are the first reported for an all-gas source MOMBE process. In addition, we have fabricated a 70 transistor decision circuit whose performance at 10 Gb/s equals or exceeds that of similar circuits made from other device technologies and growth methods. These are the first integrated circuits reported from MOMBE grown material.

12.5 Gbit/s silicon bipolar 1:4-demultiplexer IC

A silicon bipolar 1:4-demultiplexer IC is presented which can be operated up to ∼12.5Gbit/s. The channels are aligned to the outputs by two external control signals. The 370 transistor chip was fabricated with an 0.4μm emitter double polysilicon 21 GHz fT Si bipolar process and consumes ∼1.9W.

InGaAs/InP double-heterojunction bipolar transistors with step graded InGaAsP between InGaAs base and InP collector grown by metalorganic chemical vapor deposition

We have fabricated InGaAs/InP double-heterojunction bipolar transistors (DHBTs) grown by metalorganic chemical vapor deposition (MOCVD). By inserting step graded InGaAsP layers between p+-InGaAs base and n−-InP collector, the current gain of DHBTs with the graded layers was about twice as large as that without the graded layers, and the dependence of collector current on collector/emitter voltage was smaller than that without graded layers. The current gain was measured up to 2300 with 25×25 μm2 emitter area at a collector current density of 1×104 A/cm2.

Bipolar-Complementary-Metal-Oxide-Semiconductor (BiCMOS) Technology with Polysilicon Self-Aligned Bipolar Devices

An advanced bipolar-complementary-metal-oxide-semiconductor (BiCMOS) technology providing uncompromised high-performance, double polysilicon self-aligned (PSA) n-p-n bipolar and 1.25 µm gate length CMOS transistors is described. The polysilicon self-aligned-BiCMOS technology (PSA-BiCMOS) is intended for high-speed logic circuit operation at 5 V, where a high level of circuit integration and power consumption is involved. Features include vertical n-p-n transistors with a self-aligned n+ polysilicon emitter and p+ polysilicon base. The CMOS transistor features n+ polysilicon gates and lightly doped drain (LDD) NMOSFET. A process simulator, Stanford University process engineering models (SUPREM III) and device simulator, Poisson and continuity equation solver (PISCES II) were used to optimize the process steps and to enhance device characteristics, respectively. The performance of N- and PMOS transistors is comparable to those of a conventional CMOS process. The driving capability of CMOS and PSA-BiCMOS was compared according to fan-out. Compared to CMOS, PSA-BiCMOS has good driving capability from about 2.5 fan-out and PSA-BiCMOS with 1.25 µm N- and PMOS transistors and a bipolar transistor with 2 µm emitter width exhibits an average ring oscillator delay of 6.25 ns/stage at 1 pF load capacitance at 5 V.

Substantial improvement by substrate misorientation in dc performance of Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As double-heterojunction NpN bipolar transistors grown by molecular beam epitaxy

Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As NpN double-heterojunction bipolar transistors have been grown simultaneously by molecular beam epitaxy on (100) and 3° off (100) towards 〈111〉A GaAs substrates. On the tilted substrate, the current gain is significantly higher, comparable to the maximum expected value, with a marked reduction of its dependence on current and device geometry. For 10 μm×40 μm emitter devices, maximum common emitter current gains (β) of 1630 and 725 were measured at a current density of ∼6.3 kA/cm2 on the tilted and flat substrates, respectively. On the tilted substrate, both the emitter injection efficiency and base transport factor are increased. We have used compositionally graded emitter-base (e-b) and abrupt base-collector (b-c) junctions. We find that the abrupt b-c junction does not result in an offset voltage but certainly reduces the electron collection efficiency, and hence the gain, in the region where it is forward biased. The device characteristics and the current gain on both substrates were essentially independent of temperature between 25 and 100 °C, except for a slight decrease of gain with increasing temperature.

Suppression of the emitter size effect on the current gain of AlGaAs/GaAs heterojunction bipolar transistor by utilizing (NH4)2Sx treatment

The (NH4)2Sx surface treatment was applied to the AlGaAs/GaAs heterojunction bipolar transistor. The suppression of the emitter size effect on the current gain was observed for up to 4×4 μm2 emitter size devices, and 2.5 times high current gain was obtained with the improvement of the ideality factor. These results indicate that the surface recombination at emitter-base junction area are largely reduced by this treatment. The (NH4)2Sx treatment also proved to be applicable to the conventional device fabrication processes and highly reliable for the heat treatment.

Carbon and tin doped npn and pnp AlGaAs/GaAs HBTs grown by MOMBE

High performance, selfaligned processed npn and pnp AlGaAs/GaAs HBTs grown by MOMBE are reported. Tin and carbon were used as n- and p-type dopants, respectively. Cutoff frequency and maximum frequency of oscillation of 53 and 128 GHz, respectively, were obtained for npn transistors (2×5 μm2 emitter) and values of 30 and 12 GHz, respectively, were measured for pnp transistors (2×4 μm2 emitter).

MOVPE growth of highly zinc-doped bases for GaAs/AlGaAs heterojunction bipolar transistors

GaAs/AlGaAs HBT epitaxial layers with highly zinc-doped bases have been succesfully fabricated by an atmospheric pressure MOVPE method. By optimizing the growth temperature, a highly doped Zn concentration and an abrupt Zn profile can be achieved at the same time. Current gain over 40 was obtained for a graded base HBT with a high Zn concentration (5×1019 cm-3) and 25×25 μm2 emitter.

10 Gbit/s D flipflop using AlInAs/InGaAs HBTs

It is demonstrated that high speed circuits can be achieved in InGaAs HBT technology with relaxed transistor design rules. A 10 Gbit/s D flipflop has been realised using HBTs with a base thickness of 1500 Å and collector thickness of 5000 Å and with 4 μm emitter stripe width.

Carbon-doped base GaAs/AlGaAs heterojunction bipolar transistor grown by metalorganic chemical vapor deposition using carbon tetrachloride as a dopant source

Carbon tetrachloride (CCl4) has been used as a carbon doping source for the base region of a GaAs/AlGaAs Npn heterojunction bipolar transistor (HBT) grown by low-pressure metalorganic chemical vapor deposition (MOCVD). Transistors were fabricated and characterized for dc current gain, emitter-base junction ideality factor, base contact resistance, and external base resistance. Microwave characterization by S-parameter measurement was performed to determine the common emitter current gain and maximum available gain as a function of frequency. Transistors with the base contact area self-aligned to a 3×10 μm emitter finger had a dc current gain as high as 50, an emitter-base junction ideality factor of n=1.2, and a current gain cutoff frequency of ft=26 GHz. Transistors of equal emitter area without self-alignment exhibited dc current gain as high as 86, n=1.2, and ft=20 GHz. A base contact resistance of Rc=2.85×10−6 Ω cm2 and an external base sheet resistance of Rs=533.4 Ω/⧠ were measured. These preliminary results indicate that carbon doping from CCl4 may be an attractive substitute for Zn or Mg in GaAs/AlGaAs HBT structures grown by MOCVD.

High speed linear array circuit with AlAaAs/GaAs heterojunction bipolar transistors (HBTs)

Direct comparison of the performance of a digital divide-by-two implemented in a linear array configuration with an optimised layout version has been made, using AlGaAs/GaAs HBTs in 3.5 μm emitter width technology with a cutoff frequency of 40 GHz. The customised version operated up to 7.5 GHz input frequency. The linear array circuit operated up to 7.05 GHz.

8 GHz full Nyquist HBT comparator

A very high speed voltage comparator circuit implemented with self-aligned GaAlAs/GaAs heteroj unction bipolar transistors (HBTs) has been demonstrated. The 2 μm emitter width transistors have a current gain cut-off frequency of 30 GHz and a maximum oscillation frequency of 34.8 GHz. A full Nyquist test has been performed up to 8 GHz, the input sensitivity varying from 3 mV at 0.5 GHz to 30 mV at 8 GHz. The hysteresis measured under quasi-static conditions is as low as 0.5 mV.

500 mA AlGaAs/GaAs power heterojunction bipolar transistor

The current–voltage characteristics of 500 mA AlGaAs/GaAs power heterojunction bipolar transistors axe reported and the influence of case temperature on current handling capability and current gain are analysed. Current handling capabilities of 400–800 mA/mm per emitter periphery at different case temperatures have been successfully demonstrated using a low-doped GaAs layer as an emitter ballasting resistor to obtain a uniform current distribution over individual emitter fingers. A current gain of 50 at a collector current of 500 mA was realised at room temperature for three elementary devices bonded in parallel, each device comprised ten (5 × 25 μm2) emitter fingers.

AlGaAs/GaAs heterojunction bipolar transistor decision circuit

An AlGaAs/GaAs heterojunction bipolar transistor (HBT) decision circuit has been designed and characterised for optical communications, using 3.5 μm emitter width transistors with cutoff frequency of 27 GHz. The maximum bit rate for a BER of 10−9 was 4.2 Gbit/s. At 2.0 Gbit/s, the dock phase margin was 240°.

In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistor on GaAs by molecular beam epitaxy

We report on the first In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors grown on a GaAs substrate. In order to suppress the propagation of threading dislocations to the surface, a ten-period AlAs/In0.52Al0.48As (20 Å/20 Å) strained-layer superlattice was repeated twice with intervening undoped In0.52Al0.48As layers. The typical common emitter current gain in 50×50 μm2 emitter area devices was 50, with a maximum of 63, at a collector current density of 2×103 A/cm2.

Heterojunction bipolar transistor utilising AlGaSb/GaSb alloy system

A heterojunction bipolar transistor (HBT) has been fabricated using the AlGaSb/GaSb material system for the first time. The HBT structure of 100 × 100 μm2 emitter size was made by mesa-etching the molecular-beam-epitaxially grown layers. The device exhibits a current gain as high as 160 at room temperature.

High-performance AlGaAs/GaAs HBT's utilizing proton-implanted buried layers and highly doped base layers

Fabrication of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) using a proton-implanted external collector layer and a highly doped base layer is presented. Influence of the proton implantation on base-collector junction characteristics is systematically investigated. At the optimized implantation condition, a buried semi-insulating layer beneath the external base is formed without deteriorating the junction current-voltage characteristics. In a fabricated HBT with 2 µm × 10 µm emitter size, a cutoff frequency f T of 50 GHz and a maximum oscillation frequency f max of 70 GHz have been achieved.

WDM experiment using 1300/1500 nm dual-wavelength LED for single-mode fibre transmission systems

A wavelength-division-multiplexing transmission experiment using a 1300/1500 nm dual-wavelength LED modulated at 140/560 Mbit/s over 10 km of single-mode fibre has been demonstrated. This dual-LED device has a 9 μm emitter spacing between the active facets with a coupling loss of 2.3 dB through a lens/fibre coupler. The chromatic dispersion penalty for the 1500 nm channel at 560 Mbit/s was about 6-5 dB and the electrical crosstalk penalty was 2.5 dB.