AN EFFECTIVE BARRIER AGAINST THE INTERDIFFUSION OF IRON AND ZINC DOPANTS IN INP

The diffusion of iron and zinc in InP is studied with secondary-ion mass spectrometry (SIMS). Intentionally doped metalorganic-vapor-phase-epitaxy- (MOVPE-) grown layers as well as ion-implanted samples were investigated. In addition, resistivity measurements were performed on MOVPE-grown, iron-doped InP layers. The diffusion behavior of iron is strongly influenced by the presence of zinc and vice versa. In adjacent regions of iron and zinc-doped layers of InP there is a dramatic interdiffusion of both dopants. The interdiffusion process can be described with a kick-out mechanism in which iron interstitials kick out substitutional zinc. The diffusion of the iron interstitials is an extremely fast transport process in InP, but the concentration of iron interstitials remains below 5 x 10(14) at cm-3. Due to this fast transport, the interdiffusion process proceeds even through barrier layers of (undoped) InP, while in the barrier layer itself the iron concentration remains below the SIMS detection limit (< 5 x 10(14) at cm-3). A sulphur-doped, n-type layer of InP stops the diffusion of iron. The semi-insulating properties of iron-doped layers of InP are affected by the interdiffusion process of iron and zinc. Since sulphur-doped InP inhibits the interdiffusion, such a layer can be applied as a barrier layer to separate zinc-doped and iron-doped regions in InP and thus preserve the semi-insulating character of the iron-doped InP.