Something you need to create cool semiconductor devices. A highly doped profile deep (some µm) under the surface. You can use it to have a low resistance connection for vertical devices or for insulation issues. Por ejemplo:
B E C
! ! !
---+---+---+-+-+--+---------------+-+
! ! ! ! !
! \___/ ! !
\______________/ !
!
!
-----------------------------------
B U R I E D L A Y E R
------------------------------------
This is a vertical BJT. You can see a highly doped
n-diffusion (the emitter) inside a lighter doped
p-diffusion (the base). Below the buried layer,
to connect the collector to the surface, via a
highly doped n-sinker.