Dopant depth distributions as a function of growth temperature in In-doped (100)Si grown by molecular beam epitaxy

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Abstract
Indium, a deep acceptor in Si, was found, using secondary ion mass spectrometry (SIMS) and in situ Auger electron spectroscopy (AES), to segregate to the surface of (100) Si films grown by molecular beam epitaxy. The films were deposited at a rate of ∼1 μm h−1 with steady state In concentrations in bulk layers ranging from 1×1016 to 6×1017 cm−3. The amount of segregation-induced profile broadening ΔIn in (2×1)-(100) films was found from SIMS analyses to reach a maximum near a growth temperature Ts of 600 °C where ΔIn∼600 nm and to decrease at both higher and lower Ts values. ΔIn was less than the SIMS depth resolution for Ts>760 °C. Calculated In depth profiles, based upon a model which includes both thermodynamic segregation driving forces and kinetic rate limitations, were found to be in good agreement with experimental results. The shape of calculated profiles was determined primarily by a combination of the Ts-dependent In incorporation probability and the steady state ratio of the surface-to-bulk In fractions. Indium surface coverages θIn large enough to be observed by AES were obtained in layers grown under conditions corresponding to strong segregation. The surface structure of films with θIn≳0.1 was found to transform from the original (2×1) reconstruction to (3×4), as observed by in situ electron diffraction, due to the formation of an ordered In overlayer.

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