The Si incorporation probability σSi of Si and the segregation-induced broadening Δs of nominally abrupt Si doping modulations during the deposition of Ga1-xAlxAs films grown by molecular-beam epitaxy (MBE) have been measured as a function of film growth temperature Ts, alloy composition x and As2 overpressure. Si depth distributions were obtained using secondary ion mass spectrometry (SIMS) calibrated with internal standards. The inherent broadening due to the SIMS sputter profiling Δ0 was ∼6.5±1 nm. Dopant modulations generated by abrupt changes in the incident Si flux were found to exhibit broadening which varied, after subtracting the instrumental effects, from Δs≅7 nm at 600°C to 25 nm at 725°C. Thus, Si segregation during Ga1-xAlxAs MBE, while quite small compared to other dopants such as Sn, was still measurable. The fact that Δs increased with increasing Ts indicates that the segregation rate was kinetically limited over the temperature range investigated in these experiments. There was a slight tendency for an increase in Si segregation with increasing Al content in the film. However, increasing the As2 overpressure by a factor of 3 above that required to obtain an As-stabilized surface had no measurable effect on Si segregation. A lower limit for the Gibbs free energy of segregation was found to be ∼0.4 eV. The Si-incorporation probability σSi in Ga1-xAl xAs was unity at Ts≲600°C and decreased to ∼0.5 at 725°C. Varying x had no detectable effect on Si incorporation. The surface binding energy of Si on Ga1-xAlxAs (100) was estimated from the above results to be 3±0.1 eV.
ASJC Scopus subject areas
- Physics and Astronomy(all)