Understanding Ultrahigh Doping: The Case of Boron in Silicon

Using first-principles calculations, we develop a theory for ultrahigh impurity doping in semiconductors. Our study of B in Si explains why boron solubility in epitaxial growth could exceed the solid solubility to reach the kinetic solubility, and, with adequate surface passivation, to reach even higher values. We further show that the partial ionization at high B concentration, C(B), observed by experiment is predominantly an electron chemical potential effect, not a boron clustering effect. Our calculated hole concentration over a wide C(B) range is in reasonable agreement with experiments.