Evaporative antimony doping of silicon during molecular beam epitaxial growth

Abstract

At T>700 °C Sb desorbs from the Si(111) surface at a rate KDNDS and incorporates in the growing surface (1.15 Å/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.