Stability of epitaxial pseudocubic group IV-V semiconductors

The semiconductor industry has developed complex growth methods to maximize the doping of contact regions and to minimize the contact resistance in semiconductor devices. These growth methods have created highly doped Si:P and Si:As films in which concentrations of the impurity as high as 10% are introduced with no visible precipitation. This work uses density functional theory to compare the relative stability of the dopant in a submicroscopic phase. Specifically, the stabilities of the pseudocubic Si3P4, Si3As4, Ge3P4, and Ge3As4 submicroscopic phases are analyzed at the level of density functional theory. The stability of these phases is analyzed as a function of strain in two dimensions, representing epitaxial growth, and three dimensions, representing inclusions in an extended matrix. The results show that both strained and unstrained extended pseudocubic Si3P4 and Si3As4 phases are thermodynamically unstable relative to SiP and SiP2, and SiAs and SiAs2, respectively. The extended forms of pseudocubic Ge3P4 and Ge3As4 phases are also thermodynamically unstable under epitaxial strain and volumetric strain. Because this work strongly suggests that extended phases Si3P4, Si3As4, Ge3P4, and Ge3As4 are not stable under experimental growth conditions, high levels of doping of Si or Ge by P or As most likely result in the formation of dispersed dopant clusters or a dispersed phase rather than the formation of submicroscopic pseudocubic phases of the dopants. Published by the AVS.