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Why an undoped heterojunction causes potential barrier?

Physics Asked on February 16, 2021

In this image (source) a potential double-barrier was created using GaAs and AlAs lattices (undoped). Why would any potential barrier be formed, if all the bonds are electrostatically balanced (i.e. full octet)?

One Answer

This structure consists of a series of potential wells at an atomic level: A quasi-free electron can travel trough this structure, where it is attracted or weakly bound by the individual atoms. In this case, a potential well due to an Al atom (or a virtual AlAs atom) is deeper than for Ga (or a virtual GaAs atom). In a picturesque view, the free electron is therefore repelled by the AlAs barriers and will be localized in the GaAs regions.

This behavior can be approximated through a slowly varying envelope function, which "on average" gives a series of potential wells and barriers.

You should be ablew to find that in one of the first chapters of any semiconductor physics textbook.

Answered by engineer on February 16, 2021

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