Abstract: The present invention provides a source of Group V and VI atoms, and in particular arsenic atoms, usable in MBE as a growth source or a doping source. The arsenic atoms are produced in two steps. In the first step, a sublimator vaporizes solid arsenic, producing a molecular beam of arsenic tetramers and/or dimers. The molecular beam source can optionally include a cracker to produce As.sub.2 from As.sub.4. In the second step, the molecular beam impinges on a surface of a heated element, termed an atomizer, producing an output beam containing atomic arsenic. The atomizer is at a temperature above about 1200K and a pressure below about 10.sup.-3 torr or at a temperature above about 1400K and a pressure below about 10.sup.-2 torr. For other Group V and VI elements, different atomizer temperatures and pressures are used.