First-principles study of crystalline silicon hyperdoped with cobalt at a concentration exceeding the Mott limit.

We systematically studied the properties of Co-hyperdoped silicon using first-principles calculations based on density-functional theory. A series of more complex configurations, such as quasi-substitutional and paired-Co-doped structures, are considered in our study. Our calculational results indicate that the quasi-substitutional and paired-Co-doped structures can introduce several intermediate bands (IBs) in the band gap and lead to the sub-band gap absorption. The quasi-substitutional and paired-Co-doped structures exhibit red-shift in their sub-band gap absorption spectra when compared to the substitutional structure. The formation energy calculations imply that the material would exhibit thermal stability of absorption in the infrared wavelength. [ABSTRACT FROM AUTHOR]