“Growing” semiconductor materials - atomic layer by atomic layer

[@abhiastronomy]

Enjoyed the session. Good job by the team!

[@nsptdpayeldolai6039]

TIFR Mumbai is Nice

[@nsptdpayeldolai6039]

I come in Soon

[@suravikalita5588]

Enjoyed the session. Have two Qs. There was a statement "alloys allow continuous change of bandgap". What does continuous change mean here? Wikipedia explains phosphor as a substance that exhibits the phenomenon of luminescence. Phosphors are usually made from a suitable host material with an added activator. The best known type is a copper-activated zinc sulfide (ZnS) and the silver-activated zinc sulfide (zinc sulfide silver). So in your lab you prepare the phosphor (as per requirement) or get to buy it as commercial material?

[@TIFRArnab]

Thanks for your comments! Firstly, we do not make white LEDs, or even blue LEDs. As "test" structures, we have grown some blue LED structures, but we haven't made packaged devices. So we do nothing with phosphors! However, I think the world has moved from only ZnS based phosphors to more of the rare-earth-doped oxides (like Ce:YAG etc.) About the continuous change of bandgap: "Bandgap Engineering" by changing the composition what makes compound semiconductors useful. For e.g. take GaAs (~1.4eV) and InAs (~0.36eV). By adjusting the In to Ga ratio in InGaAs, one can tune the bandgap of InGaAs all the way from 1.4 to 0.36eV (any composition in the range, not just some fixed values - hence continuous change. Hope this helps. Lots of lectures/notes etc. available online that explain further.

[@suravikalita5588]

@@TIFRArnab thanks for the response 🙂