INCORPORATION PROBABILITIES AND DEPTH DISTRIBUTIONS OF ALUMINUM COEVAPORATED DURING SI(100) MOLECULAR-BEAM EPITAXY

The incorporation probabilities σA1 and dopant depth distributions CA1 (x) of aluminum co-evaporated during growth of Si(100) films by molecular beam epitaxy (silicon flux approximately 1.2×1015 cm-2 s-1 were investigated as a function of growth temperature Ts between 525 and 975°C. σA1 varied exponentially and ranged from approximately 0.2 at Ts = 525°C to approximately 9 × 10-5 with an increase in the slope of ln(σA1)vs. 1/Ts for Ts> 800°C because of desorption from a surface-accumulated aluminum overlayer. Surface-segregation-induced profile broadening resulted in profile width ΔA1∼625 nm per concentration-decade for Ts≈775°C. Increasing to values of Ts≥900°C greatly reduced aluminum surface accumulation because of rapid desorption but introduced bulk-diffusion broadening resulting in ΔA1∼90 nm per concentration-decade. Relatively abrupt profiles, ΔA1<60 nm per concentration-decade, were obtained at intermediate growth temperatures near 875°C or at lower Ts combined with rapid thermal desorption at the end of each doped layer. The maximum achievable aluminum concentration in films grown at 675°C was approximately 1 ×1018 cm-3. © 1990.