The peak positions in photoluminescence spectra of Ge wetting layers (WL) deposited at 700°C were measured versus the Ge coverage with an extremely high relative resolution of 0.025 monolayers. A nearly linear redshift of the peaks with increasing Ge coverage is observed. We derived quantitative WL composition profiles by fitting this shift, and its dependence on the deposition temperature of the capping layer (Tc), to results of band structure calculations. Despite the high growth temperature, the Ge content in the WL exceeds 80%. It is shown that the composition profile is dominated by surface segregation of Ge on Si.

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