Microscopic study of the surfactant‐assisted Si, Ge epitaxial growth
The Sb‐assisted Si, Ge epitaxial growth processes have been studied using high resolution photoemission. It is found that the initially ordered Sb monolayer on the Si(100) and Ge(100) surfaces occupies the epitaxial sites and fully saturates the surface dangling bonds. This results in a reduction of the surface energy. During the growth process, the Sb atoms and the deposited Si, Ge atoms change their positions. Sb atoms segregate to the growth front to form a new ordered layer while leaving the uniform epitaxial Si, Ge layer behind.
Limitations to the use of Sb as a Surfactant During SiGe MBE
The use of Sb as a surfactant in suppressing Ge segregation during SiGe alloy growth was investigated as a function of Sb surface coverage, Ge alloy concentration, and alloy thickness using xray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy. Unlike previous studies where Sb was found to completely quench Ge segregation into a Si capping layer, we find that Sb can not completely prevent Ge segregation while Si and Ge are being co-deposited. This results in the production of a non-square quantum well with missing Ge at the beginning and extra Ge at the end of the alloy. We also found that Sb does not relieve strain in thin films but does result in compositional or strain variations within thick alloy layers.
Evaporative antimony doping of silicon during molecular beam epitaxial growth
At T>700 °C Sb desorbs from the Si(111) surface at a rate KDNDS and incorporates in the growing surface (1.15 A/sec) at a rate KINDS where KD =1.5×109 exp(−2.46/kT), KI =7.45×10−5 exp(−0.41/kT), and NDS is the Sb surface concentration cm−2. The sticking coefficient for Sb S=KI/KD =4.9×10−14 exp(2.05/kT), ranging from 10−3 at 700 °C to 3×10−5 at 850 °C. Transient time τ=K−1D ranges from 10 sec at 980 °C to 105 sec at 600 °C. Sharp, well‐controlled doping profiles result for T>750 °C and bulk mobility is achieved up to ND ∼3×1018 cm−3.ND levels >1017 cm−3 require multimonolayer equivalent Sb coverage, but Si surface area appears to increase to provide Si‐Sb bonding for all Sb atoms. For T<650 °C KI increases and S∼unity at 600 °C.