量子尺寸效应与量子限制斯塔克效应

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量子尺寸效应【quantum size effect】

与

量子限制斯塔克【quantum-confined Stark effect (QCSE)】效应

quantum size effect：

A double heterostructure is composed of a layer of lower bandgap material bound on both sides by layers of larger bandgap material . The carriers migrate to the energetically favorable positions inside the wells, where they are confined until recombination. Figure 4.1 depicts a typical double heterostructure commonly used in nitride LED’s, in which the InGaN wells are bound on both sides by GaN barriers.

Once inside the wells, carriers act in accordance with the “particle-in-a-box” concept of quantum theory, which means that a series of discrete energy states are formed within each well (see the dotted lines in the figure), as opposed to the energy continuum seen in a bulk layer. Because of the presence of these energy quanta, double heterostructures are commonly referred to as “quantum” wells. These quantized energy states within the well lead to an effective increase in the bandgap, and thus a blueshift of the emission energy.

This phenomenon is known as the quantum size effect and must be taken into account when analyzing the emission wavelength of an LED whose active region is composed of quantum wells.



quantum-confined Stark effect (QCSE)：

When piezoelectric band-bending takes place, the conduction band minimum is shifted to a lower


energy. The valence band maximum, however, remains energetically at the same location. Thus the effective bandgap of the material is lowered; i.e. emission will be redshifted. This phenomenon is known as the quantum-confined Stark effect (QCSE)

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