The pn Junction University of Delaware(pn结特拉华大学).pdf
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The p-n Junction
ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner
The pn Junction
• The pn Junction in Equilibrium
– Built in voltage
– Carrier concentrations
– Depletion Region
• The pn Junction Under Bias
– Carrier Injection
• IV equation for pn junction
– Minority carrier current in quasi-neutral regions
– Current flow in depletion region
– Physical Meaning of I0
– Reverse breakdown
• Quasi-Fermi Levels
• Non-idealities
– Series resistance
– High Injection
– Depletion Region Recombination
ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner
pn Junction in Equilibrium
• Bring p type and n type material together physically
• Thermal equilibrium means no extra heat, no applied voltages, no
light
• The electrons from the n type material will diffuse into the p type
material (and vice versa for holes)
• After crossing the junction the electrons in the p type (holes in n
type) material are minority carriers with a recombination lifetime
• Keep in mind the dopant atoms don’t move – they are part of the
crystal
ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner
pn Junction in Equilibrium
• Movement of carriers across junction leaves ionized dopant atoms
behind
• Material is now charged since the balancing charge carrier is gone
• Electric field is now present around the junction
• Region around the junction is called the space charge region or
more commonly the depletion region (since the region surrounding
the junction is depleted of carriers)
Note: remember Electric
field direction
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