In situ optical characterization of GaAs surfaces under alternating supply of GaCl and AsH3

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Abstract
This letter describes the use of surface photoabsorption (SPA) measurements to characterize GaAs substrate surfaces under an alternating supply of GaCl and AsH3 in chloride atomic layer epitaxy (ALE). This characterization technique utilizes p-polarized light incident at the Brewster angle, which virtually eliminates the bulk contribution of the reflected light. It was found that the reflection intensity varied by several percent depending on the source gas supply sequence. This reflection intensity was constant during continuous GaCl supply, which corresponded to the self-limiting mechanism of chloride ALE. Optical reflection spectra were measured in the range of 300–800 nm during the flow of each source gas. The normalized spectra of reflection difference between GaCl and AsH3 supply depended on the incidence azimuth, which showed the existence of anisotropic surface bonds. By comparing these spectra to the reference data using triethylgallium as a Ga source, the GaAs surface under GaCl exposure was assumed to be a Ga-stabilized surface at 520 °C.