In this chapter, you will learn about: The space-charge region boundaries represent an a step junction, the abrupt depletion layer approximation applies, no carriers exist in the space-charge region, in the bulk of the diode outside the depletion region, the semiconductor is neutral. | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad I-V Characteristics of PN Junctions Lecture No: 7 PN Junction Ideal I-V Characteristics: Assumptions The space-charge region boundaries represent an a step junction. The abrupt depletion layer approximation applies. - abrupt boundaries & neutral outside of the depletion region No carriers exist in the space-charge region. In the bulk of the diode outside the depletion region, the semiconductor is neutral. Diode operation is considered at a temperature at which all impurity atoms are ionized. Perfect ohmic contacts are made to the ends of the p and n regions. The Maxwell-Boltzmann approximation applies to carrier statistics. The Concept of low injection applies. Qualitative Description of Current Flow Equilibrium Reverse bias Forward bias Current-Voltage Relationship Quantitative Approach Current-Voltage Characteristics THE IDEAL DIODE Positive voltage yields finite current Negative voltage yields zero current REAL DIODE Voltage-Current Characteristics of a P-N Junction Built-in-Potential Boundary Conditions: If forward bias is applied to the PN junction The Steady state : • Under the idealized assumptions, no current is generated within the depletion region; all currents come from the neutral regions. •In the neutral n region, there is no electric field , thus in the steady-state the solution of the continuity equation, with the boundary conditions gives: Minority Carrier Distribution Steady state condition : Steady state condition : Ideal PN Junction Current Effect of Temperature on diode Curves: Doping Levels Junction Area The Junction Temperature. All other factors may be regarded as being constant. However, temperature dependence is very strong. Total PN Junction Current Temperature Effect Js : strong function of temperature Reverse Bias-Generation Current Recombination rate of | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad I-V Characteristics of PN Junctions Lecture No: 7 PN Junction Ideal I-V Characteristics: Assumptions The space-charge region boundaries represent an a step junction. The abrupt depletion layer approximation applies. - abrupt boundaries & neutral outside of the depletion region No carriers exist in the space-charge region. In the bulk of the diode outside the depletion region, the semiconductor is neutral. Diode operation is considered at a temperature at which all impurity atoms are ionized. Perfect ohmic contacts are made to the ends of the p and n regions. The Maxwell-Boltzmann approximation applies to carrier statistics. The Concept of low injection applies. Qualitative Description of Current Flow Equilibrium Reverse bias Forward bias Current-Voltage Relationship Quantitative Approach Current-Voltage Characteristics THE .
