Structural, bonding, and elastic properties of Si:X (X = B, Al, and Ga): A theoretical study

Extremely high doping has recently been used in electrical and optical applications of semiconductor devices, but advances in doping have been hindered by poor understanding of their fundamental properties. Here, we present a theoretical study to resolve the structural, bonding, and elastic properties of Si:X alloys (X = B, Al, and Ga). Density functional theory calculations revealed the structural distortion caused by the substitutional incorporation of group IIIA elements into the Si host lattices, thus allowing an accurate comparison of both their bonding length and lattice parameters with previous experimental values. The change of atomic structure and bonding characteristics when incorporating group IIIA elements was investigated using Bader volume and charge density analyses. Furthermore, elastic properties were studied to understand the elastic behavior and the pseudomorphic growth of Si_1-xB_y, Si_1-xAl_y, and Si_1-xGa_y on Si, yielding a perpendicular lattice parameter in the growth direction. Finally, from a detailed analysis of the lattice parameters of Si_1-x-yGe_xB_y, we found that the tensile strain caused by 8.4 atom% Ge can be compensated by adding 1 atom% B in pseudomorphic Si_1-x-yGe_xB_y films. Our findings highlight the effect of doping on material properties and may open up opportunities for the design of doped semiconductor devices based on doping and epitaxial growth results.