Forward-biased Diode & Reverse-biased Diode

Chapter 9.10 Forward-biased Diode

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

  • Semiconductor Theory and Devices 273terminal. In the case of a p-n junction diode the anode is the p-type and the cathode is the n-type. In Chapter 6 it was stated that a diode will conduct in one direction but not in the other. This behaviour is explained as follows. 9.10 Forward-biased Diode Figure 9.12 shows a battery connected across a diode such that the positive terminal is connected to the anode and the negative terminal to the cathode. pn Fig. 9.12 The electric fi eld produced by the battery will cause holes and electrons to be swept toward the junction, where recombinations will take place. For each of these an electron from the battery will enter the cathode. This would have the effect of disturbing the charge balance within the semicoductor, so to counterbalance this a fresh electron-hole pair will be created in the p-type. This newly freed electron will then be attracted to the positive plate of the battery, whilst the hole will be swept towards the junction. Thus the circuit is complete, with electrons moving through the external circuit, and a movement of holes and electrons in the semiconductor. Hence, when the anode of the diode is made positive with respect to the cathode it will conduct, and it is said to be forward biased. 9.11 Reverse-biased Diode Consider what now happens when the battery connections are reversed ( Fig. 9.13 ). The electric fi eld of the battery will now sweep all the mobile holes into the p-type and all the free electrons into the n-type. This leaves a region on either side of the junction which has been depleted of all of its mobile charge carriers. This layer thus acts