Indirect Transition in indirect semicondutor material

[itsbiprangshu]

In case of indirect transition in an indirect semiconductor material, momentum as well as energy changes. I got from the book "solid state electronics devices" by Streetmen & Banerjee that in such kind of transition "the energy is generally given up as heat to latice rather than as an emitted photon". Then my query is what is the basic difference between Heat to latice & photon emmission. Beacause as per my knowledge heat is infrared & infrared emmission is nothing but low energy photon emmission. Then how the heat & photon emission are different.

 

[Defennder]

Well this is what I know. I hope I'm not too mistaken:
A photon provides very little momentum, as you can see easily from the de Broglie's relation. There is a huge change in momentum when an electron emits a phonon and drops from from the conduction to valence band (for an indirect bandgap semiconductor), whereas the momentum change due to photon emitted for a direct-bandgap semiconductor recombination is negligible.

 

[ZapperZ]

In case of indirect transition in an indirect semiconductor material, momentum as well as energy changes. I got from the book "solid state electronics devices" by Streetmen & Banerjee that in such kind of transition "the energy is generally given up as heat to latice rather than as an emitted photon". Then my query is what is the basic difference between Heat to latice & photon emmission. Beacause as per my knowledge heat is infrared & infrared emmission is nothing but low energy photon emmission. Then how the heat & photon emission are different.

"Heat to the lattice" means that the energy stays within the material in the form of lattice vibrations (phonons). This is not an EM radiation such as IR. The lattice may later on radiate this as IR, but this is not a direct result of the transition, i.e. the IR has a wider spectrum than a direct transition.

Zz.