Si incorporation probabilities and depth distributions in Ga/sub 1-x/Al/sub x/As films grown by molecular-beam epitaxy

The Si incorporation probability sigma/sub Si/ of Si and the segregation-induced broadening Δ/sub s/ of nominally abrupt Si doping modulations during the deposition of Ga/sub 1-x/Al/sub x/As films grown by molecular-beam epitaxy (MBE) have been measured as a function of film growth temperature T/sub 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 approx.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/sub s/approx. =7 nm at 6000C to 25 nm at 7250C. Thus, Si segregation during Ga/sub 1-x/Al/sub x/As MBE, while quite small compared to other dopants such as Sn, was still measurable. The fact that Δ/sub s/ increased with increasing T/sub 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 approx.0.4 eV. The Si-incorporation probability sigma/sub Si/ in Ga/sub 1-x/Al/sub x/As was unity at T/sub s/< or approx. =6000C and decreased to approx.0.5 at 7250C