Surface segregation of boron atoms in Si and strained Si1−xGex layers during MBE growth: experiment and simulation

Abstract

Boron segregation from submonolayer interfacial B deposition during molecular beam epitaxy (MBE) growth of Si1−xGex and Si layers in the temperature range 350–800 °C has been investigated by high resolution secondary ion mass spectroscopy and modeled by an atomistic description as a function of growth temperature and alloy composition.In the case of Si-MBE, beginning at 550 °C segregation-induced profile broadening occurs and at 600 C kinks appear in the boron profiles developing into shoulders for higher growth temperatures. At temperatures above 700 °C at the shoulder a concentration of (1–2) × 1019 cm−3 was found. For Si1−xGex growth the segregation is significantly reduced and a decay length of 0.6-0.8 nm can be obtained in the range 350–450 °C.From a fit of the B-profile between 450 °C and 600 °C we obtained a kinetic barrier for a jump to the surface state of approximately 2.1 eV and a Gibbsian heat of segregation of 0.44 eV in the case of Si-MBE. The transition temperature from strong surface segregation to kinetically limited segregation yields 640 °C. In the case of Si1−xGex growth the activation energy for segregation increases up to 4.5 eV for germanium, comparable with that of bulk diffusion.