* Semiconductor Bandgaps E are usually in the range: 0E 3 eV (up to 6 eV if diamond is included) Also, at equilibrium, at temperature T = 0. the valence band is full &the conduction band is empty Now, consider what happens if electromagnetic radiation ("light") is shined on the material. In the photon representation of this radiation Ifhv 2 Eg some electrons can be promoted to the conduction band leaving some holes in the valence band
Now. consider some of the yarious possible tvpes of spectra associated with this process: Looks at the number of absorbed photons (intensity) vs. photon frequency Looks at the number of retlected photons (intensity) vs photon frequency o Looks at the number of transmitted photons (intensity) Absorption Reflection anssio Looks at the numb vs. photon frequency Emission Looks at the number of emitted photons (intensity vs. photon frequency o
A (non-comprehensive) list of Various Spectra Types: Absorption, Reflection, Transmission, Emission Each of these types of spectra is very rich, complicated, & varied! . Understanding such spectra gives huge amounts of information about: electronic energy bands, vibrational properties, defects,
Interaction Between Light & Bulk Material Many different possible processes can occur! 1. Refraction 2. Transmission 3. Reflection "Semi- transparent" material Incident light a. Specular b. Total internal c. Diffused 4. Scattering There is also Dispersion where different colors bend differently
Light Interaction with Solids Reflected: IR Absorbed: A Transmitted: IT Incident: lo Optical Classification Tran pare hear strain 6 tsarainh Opaque 1816 HK'nit, (12.7)
A Quick Review of Light" & Photons History: Newton & Huygens on Light Light as waves * Light as particles Christiaan Huygens Threy strongly disagreedwith each other
Light Einstein & Planck 1905 Einstein Related the wave & particle properties of light when he looked at the Photoelectric Effect. .Planck Solved the black body radiation problem by making the (first ever) quantum hypothesis: Light is quantized into quanta (photons) of energy E hv. Wave-Particle dualiy (particles) waves) Light is emitted in multiples of a certain minimum energy unit. The size of the unit tie photon. Explains how an electron can be emitted if light is shined on a metal The energy of the light is not spread but propagates .
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