Unformatted text preview: on coefficient a for a
semiconductor on the wavelength of incident light. Optical Absorption
Band gaps of some common SC’s relative to the optical spectrum. SC’s transmit wavelengths that are larger than the bandgap Luminescence
Definition: light emission due to recombination
of excited carriers
• Photoluminescence: occurs when the electrons
were excited by photons
• Cathodoluminescence: occurs when the electrons
were excited by high-energy electron
• Electroluminescence: occurs when the electrons
were excited by injected current.
were Excitation and recombination mechanisms in SC’s
Excitation Photoluminescence with a trapping level for electrons Photoluminescence
General Mechanisms a) Incident photons generate e-h pair
b) Excited electron sheds energy to lattice by
c) Electron trapped by an impurity in the gap
d) Trapped electron remains until thermally
excited to conduction band.
e) Electron descends across the gap and
recombines with a hole and in doing so gives
off a photon
Photoconductivity: conductivity due to PL excess carriers Electroluminescence
• Common exampl...
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