Effects of S,Si, or Fe dopants on the diffusion of Zn in InP during MOCVD

Diffusion of Zn in InP during growth of InP epitaxial layers has been investigated in layer structures consisting of Zn-InP epilayers grown on S-InP and Fe-InP substrates, and on undoped InP epilayers. The layers were grown by metalorganic chemical vapour deposition (MOCVD) atT = 625° C andP = 75 Torr. Dopant diffusion profiles were measured by secondary ion mass spectrometry (SIMS). At sufficiently high Zn doping levels ([Zn] ≥8 × 10¹⁷ cm⁻³) diffusion into S-InP substrates took place, with accumulation of Zn in the substrate at a concentration similar to [S]. Diffusion into undoped InP epilayers produced a diffusion tail at low [Zn] levels, probably associated with interstitial Zn diffusion. For diffusion into Fe-InP, this low level diffusion produced a region of constant Zn concentration at [Zn] ≈ 3 × 10¹⁶ cm⁻³, due to kick-out of the original Fe species from substitutional sites. We also investigated diffusion out of (Zn, Si) codoped InP epilayers grown on Fe-InP substates. The SIMS profiles were characterised 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. For [Si] ≫ [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 these results are consistent with the presence of donor-acceptor interactions in InP, resulting in the formation of ionised donor-acceptor pairs which are immobile, and do not contribute to the diffusion process.