A method to laser anneal a silicon stack (or a silicon-rich alloy) including a heavily doped region buried beneath an undoped or lightly doped region is disclosed. By F selecting laser energy at a wavelength that tends to be transmitted by crystalline silicon and absorbed by amorphous silicon, crystallization progresses through the silicon layers in a manner that minimizes or prevents diffusion of dopants upward from the doped region to the undoped or lightly doped region. In preferred embodiments, the laser energy is pulsed, and a thermally conductive structure beneath the heavily doped layer dissipates heat, helping to control the anneal and limit dopant diffusion.