Semiconductors are materials that have band gap between that of insulators and that of conductors.

We can modify the electrical properties of semiconductors by doping the material.  For example, silicon has four valence electrons.  By doping silicon with boron (which has three electrons), we introduce holes into the valence band of silicon.  By doping silicon with phosphorus (which has five electrons), we introduce electrons in the conduction band of silicon.

Doping can be done with a variety of methods, such as ion implantation or gas phase doping.  Ion implantation is done by bombarding the material with high energy atoms.  The advantage of using ion implantation is that doping concentrations above that of the solid solubility limit can be achieved.  However, the use of ion implantation results in crystal damage, that must be fixed through an annealing step.  Ion implantation is modeled by monte carol methods.

Gas phase doping is performed by flowing the gas phase of the dopant atoms over the material.  Photoresist in photolithography or silicon oxide are often used to define the regions for doping.   This method of doping is limited by the solid solubility limit, and diffusion is used to drive the dopants into the material.

For III-V materials, such as InAs, the prospects of ion implantation do not look so favorable, as the crystal damage is more difficult to fix due to the stoichiometry of the lattice.  Researchers are currently doping these materials in-situ, by gas phase doping, or other exotic methods.

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