The migration of Zn during the growth of InP epitaxial layers was investigated in structures which consisted of Zn-InP epilayers that had been grown onto S-InP and Fe-InP substrates, and onto undoped InP epilayers. The layers were grown by means of metalorganic chemical vapor deposition at 625C, under a pressure of 75torr. The dopant diffusion profiles were measured by using secondary ion mass spectrometry. At high Zn dopant levels (greater than 8 x 1017/cm3), diffusion into S-InP substrates took place, with Zn accumulation in the substrate at a concentration which was similar to [S]. Diffusion into undoped InP epilayers produced a diffusion tail at low [Zn] levels. This was suggested to be associated with interstitial Zn diffusion. In the case of diffusion into Fe-InP, this low-level diffusion produced a region of constant Zn concentration when the dopant concentration was equal to 3 x 1016/cm3. This was attributed to kicking-out of the original Fe species from substitutional sites. Diffusion out of (Zn,Si) co-doped InP epilayers which had been grown onto Fe-InP substrates was also investigated. The secondary ion mass spectrometry profiles were characterized by a sharp decrease in [Zn] at the epilayer/substrate interface. The magnitude of this decrease corresponded to that of the Si donor level in the epilayer. When [Si] was greater than [Zn] in the epilayer, no Zn diffusion was observed. Hall measurements indicated that the donor and acceptor species in those samples were electrically active. All of the results were consistent with the presence of donor-acceptor interactions; resulting in the formation of ionized donor-acceptor pairs which were immobile and did not contribute to the diffusion process.

C.Blaauw, B.Emmerstorfer, D.Kreller, L.Hobbs, A.J.Springthorpe: Journal of Electronic Materials, 1992, 21[2], 173-9