Bipolar devices emitter-base junction

Both bipolar junction transistors (BJTs) and field-effect transistors (FETs) are charge-control devices [15]. The functions of the emitter, base, and collector electrodes of the BJT are replaced by the source, drain, and gate... 

To achieve the lowest possible delay a bipolar switching transistor developed by IBM minimizes parasitic resistances and capacitances. It consists of self-aligned emitter and base contacts, a thin intrinsic base with an optimized collector doping profile, and deep-trench isolation (36). Devices must be isolated from each other to prevent unwanted interactions in integrated circuits. While p—n junctions can be used for isolation, IBM s approach etches deep trenches in the siUcon wafer which are filled with Si02 to provide electrical insulation. 

In Figure 5-la is shown a schematic representation of a silicon MOSFET (metal-oxide-semiconductor field effect transistor). The MOSFET is the basic component of silicon-CMOS (complimentary metal-oxide-semiconductor) circuits which, in turn, form the basis for logic circuits, such as those used in the CPU (central processing unit) of a modern personal computer [5]. It can be seen that the MOSFET is isolated from adjacent devices by a reverse-biased junction (p -channel stop) and a thick oxide layer. The gate, source and drain contact are electrically isolated from each other by a thin insulating oxide. A similar scheme is used for the isolation of the collector from both the base and the emitter in bipolar transistor devices [6],... 

Bipolar transistors are realized using either an npn- or pnp-junction sequence. The different segments of the device are named as collector, base, and emitter electrode, respectively. In order to operate the transistor, one of the junctions is forward biased, while the other is biased in reverse. Using a small control current over the base electrode, a significant current between the collector and emitter electrodes is enabled. 

The bipolar transistor, which began the microelectronics revolution, consists of two diodes joined back to back by a thin common semiconductor layer (the base). Thus, bipolar transistors are referred to as p-n-p or n-p-n depending upon whether the common base layer is n or p type. Consider a typical n-p-n bipolar junction transistor, shown schematically in Figure 3.24 along with the electrical coimections for its operation. When turned on the emitter junction is forward biased. This injects electrons into the base and holes into the emitter. The holes injected into the emitter recombine there and are of no value to operation of the device. The electrons emitted into the base may either recombine, contributing to base current, or transit the base. If the base is thin, most of the electrons pass through it without recombining, reach... 

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