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PHYS3080 – Part IISemiconductors 4
Dr Neil Curson
Email: [email protected]
Office: HP Invent Centre, 1st floor, Newton building
Contact times: 6-7pm Wednesday9-10am Thursday
Electrons in solids
Gu-Yeon Wei/Harvard
Fermi energy
e.g. pn junction
Gu-Yeon Wei/Harvard
Above 0 K: Fermi-Dirac statistics
Gu-Yeon Wei/Harvard
Doped (extrinsic) semiconductors
Fermi level positions
p-typen-type
Equilibrium concentration: electrons
Gu-Yeon Wei/Harvard
Equilibrium concentration: holes
Gu-Yeon Wei/Harvard
Intrinsic semiconductors
Gu-Yeon Wei/Harvard
Temperature dependence of carrier concentrations
Gu-Yeon Wei/Harvard
Current flow
Gu-Yeon Wei/Harvard
Drude model of conductivity
Gu-Yeon Wei/Harvard
Drude model of conductivity
Gu-Yeon Wei/Harvard
Hall effect
Gu-Yeon Wei/Harvard
Diffusion
Gu-Yeon Wei/Harvard
pn junction diodes
Ideal diode
Characteristics of pn junction diode
From Sedra and SmithGu-Yeon Wei/Harvard
Current equations
Gu-Yeon Wei/Harvard
Mobile carriers
Gu-Yeon Wei/Harvard
Band diagrams
Gu-Yeon Wei/Harvard
What happens when n-type meets p-type?
Gu-Yeon Wei/Harvard
Equilibrium motion of carriers
Gu-Yeon Wei/Harvard
E-field and ‘built-in’ potential
Gu-Yeon Wei/Harvard
Junction built-in voltage
Gu-Yeon Wei/Harvard
Width of the depletion layer
Gu-Yeon Wei/Harvard
Band Diagram under Bias
PN Devices: LED and Solar Cell
• Light-emitting diode (LED)– Converts electrical input to light output: electron in → photon out– Light source with long life, low power, compact design. – Applications: traffic and car lights, large displays.
• Solar Cell– Converts light input to electrical output: photon in → electron out
(generated electrons are “swept away” by E field of pn junction)– Renewable energy source!
LED Solar Cell
