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How is a potential barrier formed in p-n junction diode ? |
Answer» Solution :Formation of junction diode. When a p-type CRYSTAL is place in CONTACT with n-type crystal so as to form one piece, the assembly so obtained is called p-n junction or junction diode or crystal diode. The SURFACE of contact of p-type and n-type crystals is called junction. In the p-section, holes are the majority carriers while in n-section, the majority carriers are electrons. Due to high concentration of different types of charge carriers in the two sections, holes from p-region diffuse into n-region and electrons from n-region diffuse into p-region. In both cases, when an electron meets a hole they cancel the effect of each other and as a result, a thin layer at the junction becomes devoid of charge carriers. This is called depletion layer as shown in the FIGURE. The thickness of depletion layer is of the order of `10^(-6)m`.  Due to the migration of holes and electrons, the two sections of the junction diode no longer remain neutral. The p-section of the junction diode becomes SLIGHTLY negative, while the n-section is rendered positive. Due to this, there is a potential gradient in the depletion layer, negative on the p-side and positive and the n-side. In other words, it appears as if some fictitious battery is connceted across the junction with its negative pole connected to p-region and positive pole connected to n-region. The potential difference developed across the junction diode due to migration of majority carriers is called potential barrier. |
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