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.