G. Lippert

Suppressed diffusion of boron and carbon in carbon-rich silicon

Transient enhanced diffusion of boron in silicon can be suppressed by substitutional carbon. We show here that diffusion of boron and carbon is strongly reduced in carbon-rich silicon, even when no supersaturation of interstitials due to implantation is present. Pronounced non-Fickian diffusion behavior was found for epitaxially grown-in carbon at concentrations well above its solid solubility. The experimentally observed suppression of B and C diffusion at high C concentrations is explained in terms of a recently proposed model that predicts an undersaturation of Si self-interstitials caused by diffusion of C out of C-rich regions.

The impact of supersaturated carbon on transient enhanced diffusion

Transient enhanced diffusion of B is strongly suppressed in C-rich Si. We show that the physical mechanism for this suppression is out-diffusion of C from regions of high C concentration. B doping superlattices with background C concentrations between 1018 and 1020 cm−3 were grown by molecular beam epitaxy and implanted with BF2 ions. The measured dependence of transient B diffusion on the C profile is explained by coupled diffusion for C and Si point defects. The proposed model is supported by the observation of transient enhanced diffusion of C.

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

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.

Two-dimensional lattice-mismatched heteroepitaxy of germanium on silicon beyond the critical thickness by introducing a surfactant

Smooth germanium films have been grown on Si(100) surfaces in a two‐dimensional fashion by using antimony as a surfactant. Different ways of depositing the surfactant (at the interface between substrate and growing film, after the deposition of a thin Ge layer, and by coevaporation) have been investigated. The grown films, investigated by high‐resolution electron microscopy and reflection high‐energy electron diffraction, show that the surfactant does not act at the interface. A kinetical approach for the description of surfactant behavior in the growing front is necessary.

Influence of carbon incorporation on dopant surface segregation in molecular-beam epitaxial growth of silicon

We describe the effect of carbon incorporation into Si on dopant surface segregation during molecular-beam epitaxial growth. Low concentration of carbon can significantly reduce the surface segregation of boron and phosphorus. Combining the surface diffusion model with a two-state exchange process, we are able to model the experimental results over the whole temperature range between 350 and 800 °C. Each exchange process alone is not sufficient to describe surface segregation at all investigated temperatures. Our results show that the presence of carbon lowers the energy difference for boron in subsurface and surface states. The energy barriers for surface diffusion as well as for the two-state exchange process are not affected by carbon.

Ternary SiGeC alloys: growth and properties of a new semiconducting material

Abstract The growth and properties of Si1−yCy and Si1−x−yGexCy alloys pseudomorphically strained on Si(001) will be critically reviewed. Although the bulk solubility of carbon in silicon is small, epitaxial layers with more than 1 at.% C can be fabricated by molecular beam epitaxy and different chemical vapour deposition techniques. One of the most crucial questions is the relation between substitutional and interstitial carbon incorporation, which has a large impact on the electrical and optical properties of these layers. We will show that the interstitial to substitutional carbon ratio is strongly influenced by the chosen growth conditions, like growth temperature and Si growth rate. In addition, angle-resolved X-ray photoelectron spectroscopy measurements indicate a surface segregation of interstitial carbon-containing complexes (more significant for higher growth temperature). Substitutionally incorporated C atoms allow strain manipulation, including the growth of an inversely strained Si1−x−yGexCy layer. Local ordering effects due to atomic size differences and the growth on reconstructed surfaces, the mechanical and structural properties, and the influence of C atoms on band structure of Si and SiGe layers will be discussed.

Surfactant-mediated growth of germanium on Si(100) by MBE and SPE

Abstract Germanium layers of 10 and 30 nm thickness have been grown on Si(100) with and without antimony as a surfactant by molecular beam epitaxy (MBE) and solid phase epitaxy (SPE) and investigated in situ by RHEED and XPS and ex situ by TEM and XRD. Without a surfactant germanium growth proceed in a typical Stranski-Krastanov mode. The system is minimizing its built-in strain energy by undergoing strain relaxation through a clustering mechanism (islanding). In all surfactant-mediated growth processes it was possible to obtain smooth layers without island formation. The influence of different ways for introducing the surfactant layer (at the interface between substrate and growing film, in the growing film below or above the critical Stranski-Krastanov thickness, or on top of the grown Ge film) will be presented. Especially in surfactant-controlled SPE, the smooth epitaxial germanium layer was obtained by passing through an island formation stage. These islands formed below 400°C are of different structure than the ones formed without a surfactant. Possible mechanism for the “smoothing out” of islands developed in the beginning stage of surfactant-controlled SPE will be discussed. The island formation stage can be completely suppressed by depositing the surfactant on top of the amorphous Ge layer before increasing the temperature.

Carbon-containing group IV heterostructures on Si: properties and device applications

We review some important material properties of Si 1-y C y and Si 1-x-y Ge x C y layers grown pseudomorphically on Si(001). This new material might overcome some of the limitations of strained Si 1-x Ge y and open new fields for device applications of heteroepitaxial Si-based systems. In addition, we demonstrated incorporating low carbon concentrations (<10 20 cm -3 ) into the SiGe region of a heterobipolar transistor (HBT) can significantly suppress boron outdiffusion caused by later processing steps. The static characteristics demonstrate that the transistors should be suitable for circuit applications. Comparing the high-frequency performance of MBE-grown SiGe:C HBTs with identically SiGe HBTs we found an increase in f T and f max by a factor of more than 2 for our chosen SiGe profile. This indicates that adding carbon enabled one to use implantation steps without affecting the boron profile, that is, it offers wider latitude in process margins.

HEAVY PHOSPHORUS DOPING IN MOLECULAR BEAM EPITAXIAL GROWN SILICON WITH A GAP DECOMPOSITION SOURCE

Doping with phosphorus in solid source silicon molecular beam epitaxy is possible using a GaP decomposition source. This source evaporates solid GaP and is combined with an efficient mass separator system. Homogeneous P doping up to concentrations higher than 1019 cm−3 was realized. Surface accumulation of phosphorus was not observed for the low growth temperature of 400 °C used in this study. The parasitic Ga incorporation is about three orders of magnitudes below the P concentration. This new phosphorus doping technique is suitable for n‐type doping in the range of 1017–1020 cm−3.

Van der Waals epitaxy of thick Sb, Ge, and Ge/Sb films on mica

We attempt to grow 20‐nm‐thick layers of Sb and Ge as well as periods of (20 nm Sb/20 nm Ge) layers on muscovite (a special form of mica) by van der Waals epitaxy under different growth conditions. The growth process was in situ investigated by reflection high‐energy electron diffraction and Auger electron spectroscopy. Epitaxial Sb layers could be obtained even at cold substrates (mica or polycrystalline Ge layers). It was not possible to grow monocrystalline Ge layers by van der Waals epitaxy. Only a formation of oriented Ge grains could be observed at higher temperatures.