Lecture 4: PN-Junction.pdf
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The document discusses the formation and characteristics of a p-n junction, which is created by doping two types of semiconductor materials: p-type and n-type. It explains the processes of diffusion and drift that occur across the junction, leading to the creation of a depletion region and an electric field. Additionally, it covers biasing conditions and the limitations of operating a p-n junction.
Lecture 4: PN-Junction.pdf
- 1. B.Sc. II Dr. Vaishali V. Deshmukh Dept. of Physics Shri Shivaji Science College, Amravati Solid State Devices-I
- 3. Meaning, Formation of pn-junction What is P-N Junction? 01 Depletion region, Diffussion, Potential barrier. Properties of pn- junction 02 Forward biasing, reverse biasing Biasing a pn- junction 03 Breakdown voltage, Knee voltage. Limitations in operating conditions of pn-junction V-I characteristics of pn-junction 04 Outline
- 4. What is pn - juction? pn-junction meaning, formation A p-n junction is an interface or a boundary between two semiconductor material types, namely the p-type and the n-type, inside a semiconductor. The p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons. In a semiconductor, the p-n junction is created by the method of doping. As we know if we use different semiconductor materials to make a p-n junction, there will be a grain boundary that would inhibit the movement of electrons from one side to the other by scattering the electrons and holes and thus we use the process of doping. We will understand the process of doping with the help of this example. Let us consider a thin p-type silicon semiconductor sheet. If we add a small amount of pentavalent impurity to this, a part of the p- type Si will get converted to n-type silicon. This sheet will now contain both p- type region and n-type region and a junction between these two regions. The processes that follow after the formation of a p-n junction are of two types – diffusion and drift. As we know, there is a difference in the concentration of holes and electrons at the two sides of a junction, the holes from the p-side diffuse to the n-side and the electrons from the n-side diffuse to the p-side. These give rise to a diffusion current across the junction.
- 5. Unbiased pn-junction When an electron diffuses from the n-side to the p- side, an ionized donor is left behind on the n-side, which is immobile. As the process goes on, a layer of positive charge is developed on the n-side of the junction. Similarly, when a hole goes from the p- side to the n-side, and ionized acceptor is left behind in the p-side, resulting in the formation of a layer of negative charges in the p-side of the junction. This region of positive charge and negative charge on either side of the junction is termed as the depletion region. Due to this positive space charge region on either side of the junction, an electric field direction from a positive charge towards the negative charge is developed. Due to this electric field, an electron on the p-side of the junction moves to the n-side of the junction. This motion is termed as the drift. Here, we see that the direction of drift current is opposite to that of the diffusion current.
- 7. Current flow in f/w bias
- 9. V-I Characteristics 1. Zero External voltage 2. Forward Bias 3. Reverse bias
- 10. Important Terms
- 11. Limitations in the operating conditions of pn-junction
- 12. THANK YOU