Typically, you should see a modulation in the signal intensity during deposition. Then, after one full monolayer was completed, you get nearly the same intensity as before and the same modulation is repeated for each layer. Sometimes you already get islands of the second layer before the first layer was completed. In that case the amplitude of the signal modulation is decreasing with increasing layer thickness. The distance between the spots should not change for epitaxial growth because you keep the original lattice parameters.

Which layer thickness do you expect after 15 minutes?

Dear Sir,

Thanks for your explanation. I expect around 30 nm thickness.

But Sir, there is always some lattice parameters mismatch between substrate and grown film. does not it affect distance between two RHEED lines?

This thickness usually corresponds to several monolayers.

Have you seen the modulation of the RHEED signal during deposition?

May be small modulation which is not observable.

but definitely no change in distance between two spots.

Bi2Se3 on GaAS(111)A

(111) direction

I mean I am using GaAs(111) substrate.

I do not know in which direction I am looking RHEED pattern after loading substrate in growth chamber.

Could you please tell me how to know that?