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Questions and Answers
What is the primary condition for avalanche breakdown to occur in a pn junction?
What is the primary condition for avalanche breakdown to occur in a pn junction?
- A large forward-biased voltage is applied
- The junction capacitance is minimized
- A sufficiently large reverse-biased voltage is applied (correct)
- The doping concentrations in the pn junction are uniform
In a one-sided pn junction, what is the breakdown voltage dependent on?
In a one-sided pn junction, what is the breakdown voltage dependent on?
- Built-in potential barrier
- Doping concentration in the high-doped region
- Junction capacitance
- Doping concentration in the low-doped region (correct)
What is the characteristic of a hyperabrupt junction?
What is the characteristic of a hyperabrupt junction?
- Junction capacitance is maximized
- Doping increases away from the metallurgical junction
- Doping decreases away from the metallurgical junction (correct)
- Doping is uniform throughout the junction
What is the purpose of using specific doping profiles in a pn junction?
What is the purpose of using specific doping profiles in a pn junction?
What type of pn junction is represented by a linearly graded junction?
What type of pn junction is represented by a linearly graded junction?
What is the function of the space charge region in a uniformly doped pn junction?
What is the function of the space charge region in a uniformly doped pn junction?
Where does a net positive charge density exist in a uniformly doped pn junction?
Where does a net positive charge density exist in a uniformly doped pn junction?
What generates the net negative charge density in the p region of a pn junction?
What generates the net negative charge density in the p region of a pn junction?
What defines the junction capacitance of a pn junction?
What defines the junction capacitance of a pn junction?
What effect does an applied reverse-biased voltage have on the potential barrier in a pn junction?
What effect does an applied reverse-biased voltage have on the potential barrier in a pn junction?
In which direction does the electric field exist in the depletion region of a pn junction?
In which direction does the electric field exist in the depletion region of a pn junction?
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Study Notes
Avalanche Breakdown
- Occurs when a sufficiently large reverse-biased voltage is applied to the pn junction
- Results in a large reverse-biased current being induced in the pn junction
Breakdown Voltage
- Derived as a function of the doping concentrations in the pn junction
- In a one-sided pn junction, the breakdown voltage depends on the doping concentration in the low-doped region
Linearly Graded Junction
- Represents a nonuniformly doped pn junction
- Expressions for the electric field, built-in potential barrier, and junction capacitance differ from those of the uniformly doped junction
Hyperabrupt Junction
- Doping decreases away from the metallurgical junction
- Advantageous in varactor diodes used in resonant circuits
Uniformly Doped pn Junction
- Formed by uniformly doping one region of a semiconductor with acceptor impurities and the adjacent region with donor impurities
- Space charge region (depletion region) is formed on either side of the metallurgical junction
Space Charge Region
- Depleted of mobile electrons and holes
- Net positive charge density exists in the n region due to positively charged donor impurity ions
- Net negative charge density exists in the p region due to negatively charged acceptor impurity ions
Electric Field and Potential Difference
- Electric field exists in the depletion region due to the net space charge density
- Direction of the electric field is from the n region to the p region
- Potential difference exists across the space charge region, known as the built-in potential barrier
Applied Reverse-Biased Voltage
- Increases the potential barrier, space charge width, and magnitude of the electric field
- Changes the amount of charge in the depletion region, defining the junction capacitance
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