Effect of Hydrogen Radicals on the Reduction of Carbon Incorporation into GaAs Grown by Using Trimethylgallium

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Abstract
Carbon incorporation into GaAs grown under an ultra-high vacuum (UHV) environment was investigated in a trimethylgallium (TMGa)-As4 or AsH3 (cracked at 850° C) system with hydrogen molecules ( H2) or hydrogen radicals ( H•). The residual carbon concentrations in GaAs layers grown at a substrate temperature of 490° C were measured by secondary ion mass spectrometry (SIMS). In the case of GaAs growth by simultaneous source supply, the introduction of H• reduced the residual carbon concentrations in epitaxial layers from 8×1019 to 7×1018 cm-3 for TMGa-As4, and from 4×1019 to 5×1018 cm-3 for TMGa-AsH3. In the case of an alternating source sup- ply of TMGa and AsH3 without hydrogen, a higher level of carbon concentrations ( 1–2×1020 cm-3) than that of the simultaneous source supply case was observed irrespective of the purge duration (10–250 s) of TMGa in UHV. The residual carbon concentrations were reduced to 6×1018 cm-3 by the injection of H• after TMGa-exposure in an alternating supply cycle, although H2 did not affect the carbon incorporation. This result indicates that the adsorbed carbon-containing species derived from TMGa, which has a residence time of more than 600 s on GaAs surfaces, can be desorbed by a reaction with H• .