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Chapter 4 Lecture - Part 1

Optical absorption band gaps of some common scs

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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 occurs were excited by photons were • Cathodoluminescence: occurs when the electrons occurs were excited by high-energy electron bombardment bombardment • 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 Photoluminescence General Mechanisms a) Incident photons generate e-h pair Incident b) Excited electron sheds energy to lattice by b) Excited scattering scattering c) Electron trapped by an impurity in the gap d) Trapped electron remains until thermally Trapped excited to conduction band. excited e) Electron descends across the gap and Electron recombines with a hole and in doing so gives off a photon off Photoconductivity: conductivity due to PL excess carriers Electroluminescence Electroluminescence • Common exampl...
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