Pnp-junctions

The second type of pnp junction transistor is the fused-junction transistor, where an n-type Ge or Si wafer is contacted on both sides with In drops and then heated the In-rich regions become the p-type E and C regions, while the n-region in the middle is the B region. 

Characteristics of same pnp junction transistor as in Figs. 9.20 and 9.21, but in a common-emitter circuit. Adapted from Terman [5]. 

One of the very best ways for producing NPN and PNP junction transistors is by diffusing dopants into the silicon. Diffusion of impurity atoms into silicon is a slow process and must be done at high temperatures without melting the silicon. Double diffusions and triple diffusions have been found useful. One double diffusion method might start with n-type silicon into which a p-type impurity is diffused (such as boron). This produces one junction. An n-type impurity (such as phosphorus) can be diffused on top of the p-type diffusion. 

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. 

Figure 3. p-Nitrophenol (PNP) adsorption isotherms (A) and distribution junctions of changes in the Gibbs free energy on the PNP adsorption (B) on carbosils prepared from glucose and Si-100.6... 

Junction transistors (Figs. 9.18A and 9.18B) can be synthesized in two ways (1) the grown-junction pnp transistor or (2) the fused-junction transistor... 

Depiction of bipolar junction transistors (A) npn and (B) pnp, and their representation in common-base or grounded-base circuit diagrams (C) npn, and (D) pnp, with the signs for positive currents I and voltages V indicated. (E) Four-terminal "black box" representation of the common-base npn circuit. After applying a small voltage vE, one measures a small current iE on the left, and on the output side one measures an output voltage vc and an output current ic the base current iB is not measured, but inferred. 

CMOS devices can develop a serious problem called latchup, in which junctions in different devices connect and form a forward-biased diode structure, leading to a catastrophic current which destroys the circuit. As illustrated in Fig. 14.5a, the latchnp is caused by the formation of a pnpn device between the terminal of VSS and VDD (see Chap. 9, Sect. 1.3). In a latchup condition, the pnpn device is biased snch that the collector current of the pnp bipolar transistor supplies a base current to the npn bipolar transistor in a positive feedback situation. The latchup can cause device function failure or even self-bumout. Figure 14.5b shows the bipolar components and resistive components of a latchup configuration. The conduction state of a pnp device requires Vq, and the conduction state... 

Junction Transistor Has two p-n junctions electrically producing potential barriers between emitter and base and between base and collector. Abbreviations include NPN and PNP. 

The "bipolar" type of transistor is usually made from the element silicon, which has been doped so it has two junctions, instead of the single junction that was described in the previous chapter on diodes. Bipolar transistors can be of either the PNP or NPN type. 

FIsaURS 2-17 Two types of BJTs. Constnjction details are shown in (a) for a pnp alloy BJT and in (b) for an npn planar transistor. Symbols for a pnp and npn BJT are shown in (c) and (d). respectively. (Note that alloy junction transistors may also be fabricated as npn types and planar transistors as pnp.)... 

After the discovery Shockley developed a basic transistor theory. Practically he replaced (in 1951) the point contact with a junction system. The bipolar junction transistor may consist of three layers, farthest out emitter and collector of p-type (compare chapter 40 SiHcon) and between them a base layer of n-type (pnp transistor). The... 

A bipolar junction transistor (BJT) can be thought of as back-to-back n-p or p-n diodes to form an npn or pnp configuration as shown in Figure 22.1. 

If a curve tracer is not available in your laboratory, you can construct the very simple transistor tester of Fig. 6.8. The tester accepts on two different sockets both NPN and PNP transistor. The two-position, two-pole switch selects either type. The tester is basically a B meter and is surely much more effective than a simple ohmmeter employed to determine whether either junction is open or not. With the tester of Fig. 6.8 you put the transistor under test on the relevant socket having previously correctly positioned the switch, and take note of the panel meter reading. If such a reading is between 0 and 3V, your transistor has to be replaced. 

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