In this article we report the effect of H plasma on the purity and transport properties of molecular beam epitaxial (MBE) grown InAs, which has attracted considerable attention for high-speed and low power electronic devices in recent years. We observed that the native oxide on the InAs surface could be desorbed at temperatures as low as 300 degrees C under H-plasma irradiation. The time required for oxide desorption increased with decreasing substrate temperature. Thick InAs was grown with H-plasma assistance on semi-insulating (SI) GaAs and on an AlAs0.16Sb0.84/InAs insulating buffer layer to investigate the effect of H plasma on the transport properties of InAs. Significant improvement of the electron mobility was observed using H-plasma assisted growth. For 6 mu m InAs grown with H plasma on SI GaAs, the electron mobilities were as high as 98 000 cm(2)/V sat 77 K and 19500 cm(2)/V s at 300 K, which represent the best published data for MBE grown InAs on GaAs. For thick InAs grown on AlAs0.16Sb0.84/InAs, the electron mobilities were as high as 420000 cm(2)/V s at 77 K and 31000 cm(2)/V s at 300 K. The free carrier concentration of InAs grown with H-plasma assistance is larger than that of the sample grown without, indicating the H plasma yields a much lower compensation ratio gamma(gamma=(N-A+N-D)/n), and moreover, the H plasma is more effective in passivating acceptors than donors in InAs. The mobility and free carrier concentration were both unchanged after thermal annealing, which are advantageous for device processing. (c) 2006 American Vacuum Society.