LATTICE LOCATION OF DIFFUSED ZN ATOMS IN GAAS AND INP SINGLE-CRYSTALS

We have investigated the saturation phenomenon of the free carrier concentration in p-type GaAs and InP single crystals doped by zinc diffusion. The free hole saturation occurs at 10(20) cm-3 for GaAs, but the maximum concentration for InP appears at mid 10(18) cm-3. The difference in the saturation hole concentrations for these materials is investigated by studying the incorporation and the lattice location of the impurity zinc, an acceptor when located on a group III atom site. Zinc is diffused into the III-V wafers in a sealed quartz ampoule. Particle-induced x-ray emission with ion-channeling techniques are employed to determine the exact lattice location of the zinc atoms. We have found that over 90% of all zinc atoms occupy Ga sites in the diffused GaAs samples, while for the InP case, the zinc substitutionality is dependent on the cooling rate of the sample after high-temperature diffusion. For the slowly cooled sample, a large fraction (approximately 90%) of the zinc atoms form random precipitates of Zn3P2 and elemental Zn. However, when rapidly cooled only 60% of the zinc forms such precipitates while the rest occupies specific sites in the InP. We analyze our results in terms of the amphoteric native defect model. We show that the difference in the electrical activity of the Zn atoms in GaAs and InP is a consequence of the different location of the Fermi level stabilization energy in these two materials.