p-n Junction Diodes & Zener Diodes
Examine depletion region physics, barrier potential, forward and reverse bias I-V characteristics, dynamic resistance, avalanche vs Zener breakdown, and voltage regulation.
Marking a lesson complete represents finishing your study of the topic; it does not denote tested mastery.
Learning Objectives
- Explain how diffusion and recombination create the depletion region and contact barrier potential V_B (0.7 V for Si, 0.3 V for Ge).
- Interpret forward and reverse I-V characteristic curves and calculate dynamic resistance r_d = ΔV / ΔI.
- Analyze Zener diode breakdown mechanics (tunneling vs avalanche) and solve voltage regulator circuits.
Core Theory & Concepts
When a p-type semiconductor and an n-type semiconductor are metallurgically joined in a single monolithic crystal, free electrons and holes diffuse across the interface until an equilibrium internal electric field halts further net migration, establishing the fundamental p-n junction.
Barrier Potential
The built-in electric field in the depletion layer creates a potential barrier: ~0.7 V for Silicon and ~0.3 V for Germanium at room temperature.
Dynamic Resistance
The AC or dynamic resistance of a forward-biased diode is the reciprocal of the slope of its I-V characteristic curve: r_d = ΔV / ΔI.
Zener Voltage Regulator
When reverse-biased beyond its breakdown voltage V_Z, a Zener diode maintains an almost constant voltage despite large variations in supply voltage or load current.
Common Misconceptions
A diode acts as a simple fixed linear resistor when forward biased.
Syllabus Topic Outline
- 1Depletion layer formation, uncovered ions, and internal electric field
- 2Forward bias: narrowing depletion layer and exponential current
- 3Reverse bias: widening depletion layer and tiny reverse saturation current (Is)
- 4Dynamic resistance r_d = ΔV / ΔI calculation from I-V curves
- 5Zener diode voltage regulator: V_out = V_Z, current limits, and load regulation