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Undoped GaAs has been successfully grown by chemical beam epitaxy (CBE) via surface decomposition process using arsine (AsH3) and trimethylgallium (TMG). Three distinct regions of temperature‐dependent growth rates were identified in the range of temperatures from 570 to 690°C. The growth rates were found strongly dependent on the V/III ratio between 5 and 30. The growth rate at low V/III ratio seems to be determined by arsenic produced on the surface, whereas at high V/III ratio it shows dependence on the adsorption of TMG. Hall measurement and photoluminescence (PL) analysis show that the films are all p‐type and that carbon impurities are primarily responsible for the background doping. Carbon concentrations have been found to be reduced by two orders of magnitude as compared to those of epilayers grown by CBE which employs TMG and arsenic obtained from precracked AsH3 in a high temperature cell. It was also found that hydrogen atoms dissociated from unprecracked AsH3 play an important role in removing hydrocarbon‐containing species resulting in a significant reduction of carbon impurities.

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