Why Si is Not Suitable for Creating Light

[dervast]

Hi i was reading yesterday in a semiconductor lessons that the Si is not suitable for creating light.. Do u know why is this happening?

 

[Gokul43201]

"Not suitable" is correct in a simplistic sense, because crystalline Silicon is not a direct band-gap material. However, over these last two years, researchers have shown that you can make Silicon based photonic devices, using the Raman effect.

http://en.wikipedia.org/wiki/Indirect_bandgap

 

[photon79]

To speak more of this, there are semiconductors with Direct band gaps and Indirect band gaps.
In direct band gap materials optical transitions are more probable eg:- GaAs. Here valance band maximum and conduction band minimum lie at same K-value.
Where as in indirect band gap materials optical processes are not dominant eg:-Si, Ge .Here VB maximum and CB minimum are at different K-values.So the incoming photon has to be excited first to a virtual state and then to the conduction minimum.

 

[dervast]

Thx a lot but how can u explain me that optical transitions in Si are not propable to occur? How the indirects bands affect these transitions

 

[Gokul43201]

Thx a lot but how can u explain me that optical transitions in Si are not propable to occur? How the indirects bands affect these transitions

This is clearly explained in the article I linked. An indirect bandgap is one when the VB maximum and CB minimum have different crystal momenta. For an electron to go from the first to the second, it needs a considerable change in momentum. A photon does not have enough momentum to make this change possible; so a photon can not facilitate this transition.