Si incorporation probabilities and depth distributions in Ga1−xAlxAs films grown by molecular-beam epitaxy

Abstract

The Si incorporation probability σ_Si of Si and the segregation‐induced broadening Δ_s of nominally abrupt Si doping modulations during the deposition of Ga_1−xAl_xAs films grown by molecular‐beam epitaxy (MBE) have been measured as a function of film growth temperature T_s, 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 Δ_s≂7 nm at 600 °C to 25 nm at 725 °C. Thus, Si segregation during Ga_1−xAl_xAs MBE, while quite small compared to other dopants such as Sn, was still measurable. The fact that Δ_s increased with increasing T_s 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 σ_Si in Ga_1−xAl_xAs was unity at T_s≲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 Ga_1−xAl_xAs (100) was estimated from the above results to be 3±0.1 eV.