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In this situation, there is a distinction between "optical band gap" and "electronic band gap" (or "transport gap"). The optical bandgap is the threshold for photons to be absorbed, while the transport gap is the threshold for creating an electron–hole pair that is not bound together. The optical bandgap is at lower energy than the transport gap.
In the simplest description of a semiconductor, a single parameter is used to quantify the onset of optical absorption: the band gap, . In this description, semiconductors are described as being able to absorb photons above E G {\displaystyle E_{G}} , but are transparent to photons below E G {\displaystyle E_{G}} . [ 2 ]
Thus, extrapolating this linear region to the abscissa yields the energy of the optical bandgap of the amorphous material. A similar procedure is adopted to determine the optical bandgap of crystalline semiconductors. [5] In this case, however, the ordinate is given by (α) 1/r, in which the exponent 1/r denotes the nature of the transition: [6 ...
Energy band gaps can be classified using the wavevectors of the states surrounding the band gap: Direct band gap: the lowest-energy state above the band gap has the same k as the highest-energy state beneath the band gap. Indirect band gap: the closest states above and beneath the band gap do not have the same k value.
In semiconductors, the band gap of a semiconductor can be of two basic types, a direct band gap or an indirect band gap. The minimal-energy state in the conduction band and the maximal-energy state in the valence band are each characterized by a certain crystal momentum (k-vector) in the Brillouin zone. If the k-vectors are different, the ...
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The model has been used to fit the complex refractive index of amorphous semiconductor materials at frequencies greater than their optical band gap. The dispersion relation bears the names of Jan Tauc and Hendrik Lorentz, whose previous works [1] were combined by G. E. Jellison and F. A. Modine to create the model.
In undoped semiconductors the Fermi level lies in the middle of a forbidden band or band gap between two allowed bands called the valence band and the conduction band. The valence band, immediately below the forbidden band, is normally very nearly completely occupied. The conduction band, above the Fermi level, is normally nearly completely empty.