Ge segregation in SiGe/Si heterostructures and its dependence on deposition technique and growth atmosphere

Abstract

Ge segregation at SiGe/Si heterointerfaces has been studied for films deposited by atmospheric pressure chemical vapor deposition (APCVD), ultrahigh vacuum CVD (UHV/CVD) and molecular beam epitaxy (MBE). Profiles were taken by secondary-ion-mass-spectroscopy (SIMS) of samples grown with these techniques at the same growth temperatures and Ge concentrations. The MBE grown profiles are dominated by segregation of Ge into the Si top layer in the temperature range from 450 to 800 °C. SiGe/Si interfaces deposited by UHV/CVD at elevated temperatures are smeared, but at 515 °C and below the interfaces are abrupt within the resolution of the SIMS. Heterostructures grown by APCVD show abrupt interfaces and no indication of Ge segregation in the investigated temperature range from 600 to 800 °C. Surface passivation by hydrogen appears to be responsible for the suppression of the Ge segregation in CVD processes.

Epitaxial growth of Si1−x−yGexCy alloy layers on (100) Si by rapid thermal chemical vapor deposition using methylsilane

“…The Si-buffer/ substrate interface is not visible, demonstrating that a clean surface was obtained prior to growth. The inverse slopes of the leading and trailing edges of the Ge profile are comparable to those reported for atmospheric pressure CVD ͑APCVD͒ SiGe layers, 30 which were 12-13 nm/decade at the alloy/substrate interface, and 2.5-3 nm/ decade at the alloy/Si-cap interface. In both cases, these slopes were set by the limitations of the SIMS measurements.…”

“…The APCVD-grown SiGe/Si structure was shown to have the lowest Ge segregation compared to that of similar structures grown by MBE and UHV/CVD, which was attributed to surface stabilization by hydrogen. 30,31 A similar mechanism can be expected in our case. The inverse slope of C at the alloy/Si-cap interface is slightly higher.…”

Analysis of high-index Si(001) surfaces by reflectance difference spectroscopy

“…22,23 Recent work by Rudkevich et al 24 has shown that rather than suppressing Ge segregation, H incorporation at elevated temperatures tends to induce Si segregation to the surface. They propose a dimer-vacancy diffusion assisted Si-Ge segregation, postulating that the Si segregation occurs more readily in regions where defects can lower the exchange barrier.…”

Influence of segregation in quantum well structures

“…In some materials systems such as GaAs AlxGal _~.As [2] this is more or less correct; any variation manifests itself as an interface roughness which can be detected optically by the so-called Stokes shift, and assessed qualitatively by the widths of the peaks in the photoluminescence (PL) spectrum and the excitation (PLE) spectrum. The situation is rather different in other systems such as InxGal xAs and SiGe where one of the components has a tendency to segregate [3,4]. A compositional variation towards the growth front leads to an asymmetry in the well potential; this paper indicates the extent of its occurrence and the effects it has on devices.…”