Heterojunction bipolar transistor

The two primary problems limiting the performance of bipolar transistors are (1) injection of current from the base to the emitter in addition to the desired emission from emitter to base, and (2) low minority carrier velocities and high recombination 

To futher optimize the efficiency of electron injection into the base relative to hole injection base to emitter, it is advantageous to maximize the fraction of the band offset that occurs in the valence band as compared to that in the conduction band (for the common straddling-gap heterojimctions foimd in most heterojunctions). Strained (pseudomorphic) SiGe on Si produces such a heterojunction with a lower conduction band offset than in the unstrained material. Even better is to use strain-compensated Sii x-yGexCy alloys that both reduce or eliminate strain in the base layer (and consequently reduce the chances of dislocation formation) and also transfer the band offset primarily to the valence band even without strain. Thus carbon doped SiGe alloys are used for HBT base layers in current devices. 

The above devices use Si and SiGe alloy bases. Similar performances are found in HBT s based on III-V materials and alloys. These devices are produced with arsenides, phosphides, and nitrides in various alloy combinations. The primary 

Even though III-V alloys and materials are far more difficult to work with in large-scale production facilities, for some applications it is useful and even necessary to go to the trouble to produce devices from these materials. 

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Some of tliese problems are avoided in heterojunction bipolar transistors (HBTs) [jU, 38], tlie majority of which are based on III-V compounds such as GaAs/AlGaAs. In an HBT, tlie gap of tlie emitter is larger tlian tliat of tlie base. The conduction and valence band offsets tliat result from tlie matching up of tlie two different materials at tlie heterojunction prevent or reduce tlie injection of tlie base majority carriers into tlie emitter. This peniiits tlie use of... 

Certain features in the PR spectra at 300 K from GaAs/Gai j,jAlj heterojunction bipolar transistor structures have been correlated with actual device performance thus PR can be used as an effective screening tool. From the observed FK oscillations it has been possible to evaluate the built-in dc electric fields in the Gai j jAlj emitter, as well as in the n—GaAs collector region. The behavior... 

Secondary Ion Mass Spectroscopy (SIMS). When the p-n junction and the GaAs/GaAlAs heterojunction are not coincident, carrier recombination occurs, reducing the current and the performance of fabricated heterojunction bipolar transistors. 

In real device structures like heterojunction bipolar transistors, certain features in the PR spectrum can be correlated with actual device performance. Thus PR has been employed as an effective contacdess screening technique to eliminate structures that have imwanted properties. 

Silicon is also alloyed with germanium (Si Gei.x) for applications such as heterojunction bipolar transistors and optical emitters... 

Heterogenous immunoassays, 14 151-152 Heteroglycans, 4 697, 702 23 64 Hetero-interface, 24 71 Heterojunction, 23 34 Heterojunction bipolar transistors (HBTs), 22 166-169... 

Field-effect transistors (FETs) Heterojunction bipolar transistors (HBTs) High electron mobility transistors (HEMTs) Metal oxide semiconductor FETs (MOSFETs) Single-electron transistors (SETs) Single-heterojunction HBTs (SH-HBTs) Thin-film transistors (TFTs) hydrogenated amorphous silicon in, 22 135... 

Principles and Analysis of AIGaAsIGaAs Heterojunction Bipolar Transistors, Juin J. Liou... 

HBT HCP HDTV HEM heterojunction bipolar transistor hexagonal close packed high definition television heat exchanger method... 

H.-U. Schreiber, Novel oxide planarization for integrated high-speed Si/SiGe heterojunction bipolar transistors, IEEE Trans. Electron Devices 43(6), 1735, 1996. 

Ge Can be alloyed with Si (ShGei J for specialized devices quantum wells, heterojunction bipolar transistors, microwave devices... 

Patton, G.L. Harame, D.L. Strock, J.-M. Meyerson, B.S. Scilla, G.-S. Graded-SiGe-base, poly emitter heterojunction bipolar transistors. IEEE Electron Device Lett. 1989, 10, 534-536. 

There has been active interest in new transistor-like devices compatible with superconductivity for a number of years (39). Part of the interest derived from difficulties in using the two-terminal Josephson device in digital circuitry. With the discovery of superconductors with transition temperatures above 77 K, the device needs and opportunities need to be reassessed. MOSFFFs, GaAs HEMT s, and heterojunction bipolar transistors (HBT s) work well at 77K, so... 

Mobile telephones incorporate multilayer III-V epitaxial heterojunction bipolar transistor wafers such as that illustrated in Figure 27.12. The p-n junctions on either side of the base layer are a crucial feature of semiconductor devices, and in the wafer shown in Figure 27.12 (and in other similar wafers), the p-type base layer must be highly doped to provide high-frequency performance. Choice of dopant is critical, e.g. use of a Zn dopant (see below) results in its diffusion into the emitting n-type layers. This problem has been overcome by doping with C which exhibits a low diffusion coefficient C-doped wafers have been used commercially since the early 1990s. 

Fig. 27.12 Typical components in a multilayer heterojunction bipolar transistor wafer, each deposited by CVD.

Figure 4-30. Schematic of heterojunction bipolar transistor (HBT) device.

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