The Shockley Diode

Chapter 7.3 The Shockley Diode

Lessons In Electric Circuits Volume III – Semiconductors Book
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Lessons In Electric Circuits Volume III – Semiconductors Book

  • 324CHAPTER 7. THYRISTORS• More advanced gas-discharge tubes have been made with control elements so that their”turn-on” voltage could be adjusted by an external signal. The most common of thesetubes was called the thyratron.• Simple oscillator circuits called relaxation oscillatorsmay be created with nothing morethan a resistor-capacitor charging network and a hysteretic device connected across thecapacitor.7.3The Shockley DiodeOur exploration of thyristors begins with a device called the four-layer diode, also known asa PNPN diode, or a Shockley diodeafter its inventor, William Shockley. This is not to beconfused with a Schottky diode, that two-layer metal-semiconductor device known for its highswitching speed. A crude illustration of the Shockley diode, often seen in textbooks, is a four-layer sandwich of P-N-P-N semiconductor material, Figure 333,7.5.AnodeCathodePPNNFigure 7.5:Shockley or 4-layer diodeUnfortunately, this simple illustration does nothing to enlighten the viewer on how it worksor why. Consider an alternative rendering of the device’s construction in Figure 333,7.6.AnodeCathodePPNNNPFigure 7.6:Transistor equivalent of Shockley diode