P–N Junction Diodes

P–N Junction Diodes are the simplest type of semiconductor. They allow current to flow in only one direction. The knowledge of semiconductors that is acquired by studying diodes is also applicable to other types of semiconductor devices


When pure or intrinsic semiconductor material is doped with a pentavalent or trivalent material, the doped material is called N- or P-type based on the majority carrier. The electrical charge of each type is neutral because each atom contributes an equal number of protons and electrons

Independent electrical charges exist in each type of semiconductor material, because electrons are free to drift. The electrons and holes that drift are referred to as mobile charges. In addition to the mobile charges, each atom that gains an electron has more electrons than protons and assumes a negative charge.
Similarly, each atom that loses an electron has more protons than electrons and therefore assumes a positive charge. As described in Chapter 10, these individual charged atoms are called negative and positive ions.
There is always an equal number of mobile and ionic charges within N-type and P-type semiconductor materials.


When a voltage is applied to a diode, it is referred to as a bias voltage. above Figure shows a P–N junction diode connected to a voltage source. A resistor is added for limiting current to a safe value.


Both germanium and silicon diodes can be damaged by excessive heat and excessive reverse voltage. Manufacturers specify the maximum forward current (IF max) that can be handled safely. They also specify the maximum safe reverse voltage (peak inverse voltage, or PIV). If the PIV is exceeded, a large reverse current flows, creating excess heat and damaging the diode.


The P–N junction of a diode may be one of three types: a grown junction, an alloyed junction, or a diffused junction. Each involves a different construction technique.


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