The diffusivity was measured by using secondary ion mass spectrometry. Deliberately doped metalorganic vapor phase epitaxial layers, as well as ion-implanted samples, were investigated. In addition, resistivity measurements were performed on Fe-doped layers. It was found that the diffusion behavior of Fe was strongly affected by the presence of Zn, and  vice versa. In adjacent regions of Fe-doped and Zn-doped layers, there was a marked interdiffusion of the dopants. The interdiffusion process could be described in terms of a kick-out mechanism in which Fe interstitials kicked out substitutional Zn. The diffusion of Fe interstitials was an extremely fast transport process, but the concentration of Fe interstitials remained below 5 x 1014/cm3. Due to the rapid transport, interdiffusion proceeded even through barrier layers of (undoped) InP. In the barrier layer itself, the Fe concentration remained below the secondary ion mass spectrometric detection limit of 5 x 1014/cm3. It was found that a S-doped n-type InP layer prevented the diffusion of Fe. The semi-insulating properties of Fe-doped InP were affected by the interdiffusion of Fe and Zn. Since S-doped InP inhibited interdiffusion, such a layer could be used as a barrier in order to separate Zn-doped and Fe-doped regions, and thus preserve the semi-insulating character of the Fe-doped InP.

E.W.A.Young, G.M.Fontijn, C.J.Vriezema, P.C.Zalm: Journal of Applied Physics, 1991, 70[7], 3593-9