First-principles study of the origin of retarded diffusion of boron in silicon in the presence of germanium

Abstract

Dopant diffusion plays an important role in the formation of ultrashallow junctions. To avoid unwanted transient enhanced diffusion of dopants, especially boron, other species (e.g., Ge, C, N, and F) are introduced into the Si substrate. Here, ab initio calculations have been carried out using a density functional theory code, DFT+ +, to investigate the origin of the experimentally observed retardation of boron diffusion in SiGe alloys. The formation energies of individual Si, B, and Ge point defects, and Si-B, Ge-B, and Si-Ge pair defects were calculated. Based on these calculations, the energetics of Si: Ge: B systems suggest that one mechanism to retard boron diffusion involves the effect of Ge atoms to decrease the number of available Si self-interstitials by increasing the migration energy and, concomitantly, to increase the migration energy of boron atoms. Our results also show that it is difficult for a Ge interstitial to approach a substitutional boron atom compared with a Si self-interstitial.

Germanium diffusion mechanisms in silicon from first principles

“…These results are in good agreement with those presented by Wang et al, 9 except for Ge T . According to Wang et al, 9 Ge T is a stable defect, whereas our calculations show unstable behavior. This mismatch may be related to imposing or not imposing symmetry during the calculations: we found a stable tetrahedral defect when symmetry constraints were imposed ͑with a similar formation energy compared to that of Wang et al 9 ͒; on the contrary, when the symmetry is removed, the tetrahedral defect relaxed to a hexagonal defect.…”

Oxygen defect processes in silicon and silicon germanium

“…115,116 Ge codoping p-type or n-type dopants affect the photovoltaic properties of Si. [117][118][119][120][121][122][123][124] Considering B codoping Ge improves segregation redistribution of boron during the thermal oxidation of Si and importantly limits the formation of boron-O defects. 118,119 Notably, boron-O defects in solar cells can induce significant degradation of carrier lifetime, leading to a reduction of the energy conversion efficiency of the cell.…”

Vacancy-oxygen defects in silicon: the impact of isovalent doping

“…Ge doping has been found to retard and suppress thermal donor formation [123,124] Ge codoping with Ga, As, P and B modifies the Si material properties and affects PV characteristics [126][127][128][129]. Importantly, it improves the diffusion segregation redistribution of boron and phosphorus during thermal oxidation of Si and also suppresses the formation of boron-oxygen defects [127,130]. The presence of the latter defects in solar cells causes significant degradation of carrier lifetime, leading to a 2-3% loss of the energy conversion efficiency of the cell.…”