Chapter 4
JUNCTIONS IN
SEMICONDUCTORS: P-N
DIODES
4.1 Introduction ....................................
In the introduction to this textbook we examined how semiconductor devices are driving mod-
ern information technology. Cell phones, computer, internet, etc. all depend upon devices that
will be discussed in the next several chapters. Semiconductor diodes (and Schottky diodes) dis-
cussed in this and the next chapter have rectifying properties.p-ndiodes can be used as detectors
and light emitters. Devices such as field effect and bipolar transistors are used for amplification
and signal generation. They can also be used in digital technology as ON/OFF switches.
Semiconductor devices operate on the basis of the basic principle that the conducting and
optical properties of semiconductors can be altered easily and rapidly. One way this can be
done is through the use of junctions between dissimilar materials. Junctions can form between
n−type andp−type materials, between materials with different bandgaps, and between metals
and semiconductors. In this chapter we will discuss thep-njunction.
4.2 P-NJUNCTIONINEQUILIBRIUM .......................
Thep-njunction is one of the most important junctions in solid-state electronics. The junction
is used as a device in applications such as rectifiers, waveform shapers, variable capacitors,
lasers, detectors, etc. The key ingredient of the bipolar transistor, which is one of the most
important electronic devices is ap-njunction,. To understand how ap-njunction operates we
need to know: i) What are the carrier distributions for electrons and holes in the material? ii)
What are the physical processes responsible for current flow in the structure?