Bipolar junction rectifier

In addition to its use as a rectifier, the p—n junction (26) is the fundamental building block for bipolar, junction EFT (fFET), and MOSFET transistors. A thorough understanding of p—n junctions explains much of transistor behavior. The theory (5) of the p—n junction and its role in bipolar transistors was presented within a year of the discovery of the point-contact transistor. 

When an np rectifier is connected, through a shared p region, to a pn rectifier, we have a npn junction "triode" transistor, or bipolar junction transistor (BJT). This transistor can amplify signals, just as does the vacuum-tube triode, but by a totally different mechanism. 

Central to electronics is the IV measurement—that is, the measurement of the electrical current I through a device, as a function of the electrical potential, or bias, or voltage V placed across it. Electrical devices are most often "passive" two-terminal devices (resistors, capacitors, inductors, rectifiers and diodes, NDR devices), or "active" three-terminal devices (triodes, bipolar junction transistors, or field-effect transistors (FET)). 

Let us consider a composite rust layer consisting of an anion-selective inner layer and a cation-selective outer layer as shown in Figure 22.33a. A bipolar ion-selective layer of this type may be realized when the outer part of an anion-selective layer is made cation-selective by the adsorption of multivalent anions. As with the electronic rectifier of p-n junction semiconductors, a bipolar junction consisting of an anion-selective layer and a cation-selective layer rectifies the ionic current across the bipolar layer. The ion transfer current in the anodic direction is thus suppressed across the bipolar layer as shown in Figure 22.34, where the anodic ion transport current is seen to be restricted across a bipolar ferric hydroxide membrane in sodium chloride solution [70]. 

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