Impact of low carbon concentrations on the electrical properties of highly boron doped SiGe layers

Abstract

We present results on the effect of carbon coevaporation by molecular beam epitaxy on electrical properties of highly boron doped SiGe:C layers for C concentration of around 1020 cm−3. Such C concentrations are needed for substantial suppression of boron outdiffusion. The concentration of electrically active boron and the hole mobility are not affected by the addition of carbon. Carbon-related defects, typically observed for C concentrations below the bulk solid solubility limit (<1018 cm−3), do not significantly reduce the concentration of electrically active B in SiGe:C. However, carbon coevaporation affects carrier lifetimes. The generation lifetime is reduced by more than one order of magnitude in SiGe:C compared with analogous SiGe layers.

Issues on the molecular-beam epitaxial growth of p-SiGe inverted-modulation-doped structures

“…These observations suggest that a surface accumulation layer of approximately 1ϫ10 12 during the boron doping, but that this is increasingly ''stabilized'' by growth interruption, so that only a fraction of it segregates to dope subsequently deposited material. The origin of this stabilization phenomenon could be the C or O containing impurities that have accumulated on the surface during interruption 13 -species which are known to inhibit boron diffusion, or due to some reconstruction of the accumulated boron, including clustering. In subsequent experiments we adopted a 40 min growth interruption 3-5 nm after growing doped layer as a compromise practical solution to minimize boron segregation.…”

Effects of carbon on boron diffusion in SiGe: Principles and impact on bipolar devices

“…This capturing should lead to the formation of carbon interstitial pairs, that could act as scattering or recombination centers, and thus influence charge carrier properties. In a recent publication, 4 we described some effects of carbon on the electrical properties of highly boron-doped SiGe:C layers for C concentration of around 10 20 cm Ϫ3 . We found no significant influence of carbon on charge carrier concentration and hole mobility.…”

“…In particular, C does not reduce the electrical activity of boron. 4 The concentration of C in the investigated epitaxial layers exceeds the solid solubility limit by several orders of magnitude. 8 These C-rich layers form a metastable state with the majority of C atoms incorporated on substitutional sites.…”

Fermi level position at metal Si1−x−yGexCy interfaces

“…C defects in Si have been studied in detail, and in particular the interactions of C with B to form a complex. 52,53 The large value of ⌽ Bp ϩ⌽ Bn has its origin in the high value of ⌽ Bp , and then could be connected to these defects with C in p-type B-doped layers. Moreover, recent investigations have also demonstrated that lateral inhomogeneities have to be taken into account to explain most of the experimental results on Schottky diodes, and in particular high values of the ideality factor.…”