Why pn junction possess capacitance

Diffusion capacitance is also sometimes referred as storage capacitance. It is denoted as C D. In a forward biased diode, diffusion capacitance is much larger than the transition capacitance. Hence, diffusion capacitance is considered in forward biased diode. When forward bias voltage is applied to the p-n junction diode, electrons majority carriers in the n-region will move into the p-region and recombines with the holes.

In the similar way, holes in the p-region will move into the n-region and recombines with electrons. As a result, the width of depletion region decreases. The electrons majority carriers which cross the depletion region and enter into the p-region will become minority carriers of the p-region similarly; the holes majority carriers which cross the depletion region and enter into the n-region will become minority carriers of the n-region. When the width of depletion region decreases, the diffusion capacitance increases.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content. Dhirendra Yadav. No Comments. P-N Junction: P-N junction diode is the most fundamental and the simplest electronics device.

Capacitance of P-N Junction Diode: Any variation of the charge within a p-n diode with an applied voltage variation yields a capacitance which must be added to the circuit model of a p-n diode. Q: What is pn junction capacitance? Write your answer Related questions. Which type of capacitance effect exhibited by pn junction when it is rreverse bias? Which junction has least junction capacitance?

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Why potential across pn junction is called potential barrier? Is Gunn diode a PN junction? How depletion region is narrowed during forward biasing? Barrier potential in a pn junction is caused by? However, they exert electric field or electric force. Therefore, charge is stored at the depletion region in the form of electric field. The ability of a material to store electric charge is called capacitance. Thus, there exists a capacitance at the depletion region.

The capacitance at the depletion region changes with the change in applied voltage. When reverse bias voltage applied to the p-n junction diode is increased, a large number of holes majority carriers from p-side and electrons majority carriers from n-side are moved away from the p-n junction. As a result, the width of depletion region increases whereas the size of p-type and n-type regions plates decreases. We know that capacitance means the ability to store electric charge.

The p-n junction diode with narrow depletion width and large p-type and n-type regions will store large amount of electric charge whereas the p-n junction diode with wide depletion width and small p-type and n-type regions will store only a small amount of electric charge. Therefore, the capacitance of the reverse bias p-n junction diode decreases when voltage increases. In a forward biased diode , the transition capacitance exist. However, the transition capacitance is very small compared to the diffusion capacitance.

Hence, transition capacitance is neglected in forward biased diode. The amount of capacitance changed with increase in voltage is called transition capacitance. The transition capacitance is also known as depletion region capacitance, junction capacitance or barrier capacitance.

Transition capacitance is denoted as C T. The change of capacitance at the depletion region can be defined as the change in electric charge per change in voltage. The transition capacitance can be mathematically written as,. Diffusion capacitance occurs in a forward biased p-n junction diode. Diffusion capacitance is also sometimes referred as storage capacitance. It is denoted as C D.