A shallowp+layer with a steep boundary was obtained by Zn ion implantation and a capless annealing in an arsenic ambient. A capped annealing with a plasma deposited Si3N4film resulted in a carrier concentration profile broadened by the diffusion enhanced by the interfacial stress between the capping film and the semiconductor. Thep+layer had a peak carrier concentration of 8×1019cm−3and a thickness of less than 1000 A˚. Arsenic pressure in the annealing ambient also suppressed the enhanced diffuison of Zn in the ion‐implanted GaAs.