In-diffusion profiles of S were determined by means of secondary ion mass spectroscopy. In order to evaluate the shapes of the profiles, a set of coupled reaction-diffusion equations was solved numerically. From the simulated non-equilibrium profiles of in-diffusing S, which migrated via the kick-out mechanism, both the diffusion coefficient (figure 20) and the equilibrium concentration of As self-interstitials were determined simultaneously. The S diffusivity could be described by:

D (cm2/s) = 1.9 x 10-3 exp[-2.4(eV)/kT]

Transmission electron microscopy revealed that, due to an As supersaturation, extrinsic dislocation loops formed. The Fermi-level effect was more pronounced at lower diffusion temperatures, and provided an additional driving force for loop formation. This agreed well with the occurrence of larger faulted loops at a diffusion temperature of 950C, rather than 1100C. The complex behavior of S in-diffusion could be quantitatively described by taking account of extended defects.

Determination of Arsenic Diffusion Parameters by Sulfur In-Diffusion in Gallium Arsenide. B.F.Scholz, P.Werner, U.Gösele, N.Engler, H.S.Leipner: Journal of Applied Physics, 2000, 88[12], 7045-50

Figure 20

Diffusivity of S in GaAs