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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 ]
To understand how band structure changes relative to the Fermi level in real space, a band structure plot is often first simplified in the form of a band diagram. In a band diagram the vertical axis is energy while the horizontal axis represents real space. Horizontal lines represent energy levels, while blocks represent energy bands.
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 ...
Band diagram for straddling gap, n-n semiconductor heterojunction at equilibrium. The behaviour of a semiconductor junction depends crucially on the alignment of the energy bands at the interface. Semiconductor interfaces can be organized into three types of heterojunctions: straddling gap (type I), staggered gap (type II) or broken gap (type ...
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 ...
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[1] [3] E g is the optical energy band gap of the material. A, B, and C depend on the band structure of the material. They are positive constants such that 4C − B 2 > 0. Finally, n(∞), a constant greater than unity, represents the value of n at E = ∞.