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The exact reverse of radiative recombination is light absorption. For the same reason as above, light with a photon energy close to the band gap can penetrate much farther before being absorbed in an indirect band gap material than a direct band gap one (at least insofar as the light absorption is due to exciting electrons across the band gap).
This is usually silica, which has a much lower refractive index (of about 1.44 in the wavelength region of interest [63]), and thus light at the silicon-silica interface will (like light at the silicon-air interface) undergo total internal reflection, and remain in the silicon. This construct is known as silicon on insulator.
Electrons can gain enough energy to jump to the conduction band by absorbing either a phonon (heat) or a photon (light). A semiconductor is a material with an intermediate-sized, non-zero band gap that behaves as an insulator at T=0K, but allows thermal excitation of electrons into its conduction band at temperatures that are below its melting ...
It is evaluated by fitting the absorption coefficient as a function of energy to an exponential function. It is often used to describe electron transport in structurally disordered semiconductors such as hydrogenated amorphous silicon. [1]
[1]: 128 It is related to the absorption coefficient, , through: [39]: 41 = These values depend upon the frequency of the light used in the measurement. That κ corresponds to absorption can be seen by inserting this refractive index into the expression for electric field of a plane electromagnetic wave traveling in the x -direction.
A. R. Forouhi and I. Bloomer deduced dispersion equations for the refractive index, n, and extinction coefficient, k, which were published in 1986 [1] and 1988. [2] The 1986 publication relates to amorphous materials, while the 1988 publication relates to crystalline.
An overview of absorption of electromagnetic radiation.This example shows the general principle using visible light as a specific example. A white light source—emitting light of multiple wavelengths—is focused on a sample (the pairs of complementary colors are indicated by the yellow dotted lines).
The refractive index of silicon is 3.96 (at 590 nm), [2] while air's refractive index is 1.0002926. [3] In general, a flat-surface uncoated LED semiconductor chip emits only light that arrives nearly perpendicular to the semiconductor's surface, in a cone shape referred to as the light cone, cone of light, [4] or the escape cone. [1]