Pnp Heterojunction Bipolar Transistors Research Articles

Minority hole mobility in n+GaAs

The minority hole diffusivity, or equivalently the hole mobility, was measured in n+GaAs with the zero-field time-of-flight technique. The minority hole mobility was measured for the donor doping range of 1.3×1017 cm−3 to 1.8×1018 cm−3 and was found to vary from 235 to 295 cm2/V s. At the lower doping level, the minority hole mobility is comparable to the corresponding majority hole mobility, but at 1.8×1018 cm−3 the minority hole mobility was 30% higher than the majority carrier hole mobility. These results have important implications for the design of devices such as solar cells and pnp-heterojunction bipolar transistors.

Selective molecular-beam epitaxy for integrated npn/pnp heterojunction bipolar transistor applications

We have developed a selective molecular-beam epitaxy (MBE) growth process for the production of complementary npn and pnp heterojunction bipolar transistors (HBTs) on the same GaAs substrate. The resulting devices have excellent dc and microwave characteristics, with no degradation observed due to the additional growth and processing steps required to monolithically integrate npn and pnp HBTs. We believe the ability to fabricate high-quality complementary HBT devices and circuits will greatly expand the application base of MBE-grown heterojunction bipolar transistors.

Growth of Pnp heterojunction bipolar transistor structures by metalorganic molecular beam epitaxy

Fabrication of high-quality Pnp heterojunction bipolar transistors has traditionally been difficult due to the inability to achieve and confine high p- and n-type doping levels using common dopants such as Be and Si. In this paper we discuss how carbon and tin can be incorporated during growth by metalorganic molecular beam epitaxy in order to produce Pnp structures. In particular it has been found that carbon introduced from trimethylgallium can be used to produce abrupt, thermally stable profiles in AlGaAs and that incorporation at concentrations up to mid-1019 cm−3 does not adversely affect the optical or structural quality of the material. In addition, we have found that the use of tetraethyltin (TESn) for tin doping of the GaAs base layer allows for higher doping and better confinement of the dopant than can be obtained with elemental Sn. Consequently, large-area (90-μm diameter) Pnp transistors fabricated from material grown with TESn show higher gain than those grown with elemental tin, in spite of the higher base dopant concentration. The gain obtained with TESn, 45, is the highest yet reported for an abrupt-junction, uniformly-doped Pnp structure. Furthermore, because of the low parasitic resistances which result from the use of carbon and tin doping, the I–V characteristics obtained in this study show superior performance relative to previously published reports.

High frequency Pnp AlGaAs/InGaAs heterojunction bipolar transistor with an ultrathin strained base

High performance Pnp AlGaAs/InGaAs heterojunction bipolar transistors (HBTs) have been fabricated. The transistors have a 300 A strained InGaAs base, with indium composition linearly graded from 0 to 15%. The cutoff frequency and maximum oscillation frequency for a transistor with emitter area of 2 × 8 μm2 are measured to be 23.3 GHz and 40 GHz, respectively, at a collector current of −10 mA. These are the highest published results for Pnp HBTs.

AlGaAs/GaInAs strained-base pnp heterojunction bipolar transistors

We report the first strained-layer pnp heterojunction bipolar transistors fabricated in the AlGaAs/GaInAs/GaAs system. Despite significant lattice mismatch between the Ga0.9In0.1As base layer and AlGaAs emitter, the current gain was comparable to that of similar AlGaAs/GaAs transistors. A maximum gain of 35 was observed for a device with graded In content across the base.

Npn and pnp GaInP/GaAs heterojunction bipolar transistors grown by MOCVD

Both Npn and Pnp heterojunction bipolar transistors were fabricated using the GaInP/GaAs system for the first time by MOCVD to investigate the band lineup of the GaInP/GaAs system. By comparing the collector current, current gain and offset voltage of the Npn and the Pnp HBTs, most of the bandgap difference was found to be in the valence band.

GaAs/AlGaAs heterojunction Pnp bipolar transistors grown on (100) Si by molecular beam epitaxy

GaAs/AlGaAs Pnp heterojunction bipolar transistors (HBTs) were fabricated and tested on (100) Si substrates for the first time. A common-emitter current gain of β=8 was measured for the typical devices with an emitter area of 50×50 μm^2 at a collector current density of 1×10^(4) A/cm^2 with no output negative differential resistance up to 280 mA, highest current used. A very high base-collector breakdown voltage of 10 V was obtained. Comparing the similar structures grown on GaAs substrates, the measured characteristics clearly demonstrate that device grade hole injection can be obtained in GaAs on Si epitaxial layers despite the presence of dislocations.

Scaling in Npn and Pnp heterostructure bipolar transistors

Calculating the cutoff frequency fT of bipolar transistors from the emitter-to-collector delay neglects the heavy influence of parasitic reactances on the frequency response of realistic transistors. A more complete equivalent circuit modelling reveals that the speed advantage of Npn against Pnp heterojunction bipolar transistors of common geometry, base width, and doping profile decreases as the transistor is scaled up in size. For power applications, the fT of InP/GaInAs Pnp devices may even surpass that of Npn transistors.