Solid source molecular beam epitaxy Si growths were done with and without atomic hydrogen (AH) to investigate the impact of AH on B segregation and activation. A series of 3 or 50 nm thick B-doped Si layers separated by 200 nm of undoped Si were grown at 0.1 nm/s on Si(100) substrates. In separate experiments, 10(-4) Pa of AH was applied after (at 500, 600, and 710 degrees C) or during (at 710 degrees C) the 3 nm B-doped layer to determine if AH affected segregation. AH was applied before the 50 nm B-doped layer to observe if AH increased B activation between 600 and 800 degrees C. It was found that application of AH after the growth of the 3 nm B-doped layer had no effect on B segregation through 600 degrees C and increased B segregation at 710 degrees C, as measured by secondary ion mass spectrometry (SIMS). Application of AH during B-doped Si layer growth had no effect on B segregation. Application of 10(-3) Pa of AH for 100 s prior to growth of the 50 nm B-doped layer improved surface order, as measured by low energy electron diffraction, and, at T greater than or equal to 700 degrees C, increased B activation, as measured by spreading resistance profilometry (SRP). The differences between the SIMS and SRP data are postulated to be due to two forms of B : one electrically active and the other electrically inactive. The electrically inactive form is modeled by two paired B atoms on adjacent substitutional sites. [S0734-2101(98)07304-7].