The p-n Junction Diode

Chapter 9.9 The p-n Junction Diode

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • 272Fundamental Electrical and Electronic Principles Due to their random movement some of the electrons will diffuse across the junction into the p-type, and similarly some of the holes will diffuse across into the n-type. This effect is illustrated in Fig. 9.11 , and from this fi gure it may be seen that region x acquires a net negative charge whilst region y acquires an equal but positive net charge. The region between the dotted lines is only about 1 m wide, and the negative charge on x prevents further diffusion on electrons from the n-type. Similarly the positive charge on y prevents further diffusion of holes from the p-type. This redistribution of charge results in a potential barrier across the junction. In the case of silicon this barrier potential will be in the order of 0.6 to 0.7 V, and for germanium about 0.2 to 0.3 V. Once again note that although there has been some redistribution of charge, the sample of material as a whole is still electrically neutral (count up the numbers of positive and negative charges shown in Fig. 9.11 ). pn Fig. 9.10 npChargeyx Fig. 9.11 9.9 The p-n Junction Diode A diode is so called because it has two terminals: the anode, which is the positive terminal, and the cathode, which is the negative