Diffusion in Semiconductors
When we talk about atomic diffusion in semiconductors, we’re referring to the movement of atoms, including host atoms, dopants, and impurities. You can see diffusion happening in all thermodynamic phases, but it’s the solid phase that really matters for semiconductors.
What is Diffusion in a Semiconductor?
Diffusion describes the flow of dopant atoms through the semiconductor material’s crystal lattice. Dopants are purposefully added impurity atoms to a semiconductor in order to change its electrical characteristics. Diffusion is the process by which dopant atoms move along a concentration gradient from high concentration areas to low concentration areas.
In the process of fabricating semiconductor devices, diffusion is essential, especially when it comes to the creation of junctions in transistors and diodes. In semiconductors, diffusion processes primarily fall into two categories:
When dopant atoms are added to a semiconductor material and allowed to diffuse through it naturally—without the need for external energy sources—this process is known as intrinsic diffusion. Dopant atoms diffuse through the crystal lattice in this process, which is dependent on thermal energy, by hopping randomly from
Intrinsic diffusion
When dopant atoms are added to a semiconductor material and allowed to diffuse through it naturally—without the need for external energy sources—this process is known as intrinsic diffusion. The process is dependent on thermal energy, whereby dopant atoms randomly jump from one lattice site to another, diffusing through the crystal lattice.
Extrinsic Diffusion
In order to hasten the diffusion of dopant atoms into the semiconductor material, extrinsic diffusion uses outside energy sources like heat or ion implantation. More control over the doping profile and junction depth of semiconductor devices is possible with this technique.
In the production of many semiconductor devices, such as bipolar junction transistors (BJTs), field-effect transistors (FETs), and pn junctions, diffusion is an essential step.