A model of Cr in GaAs

We have developed a model of Cr in GaAs which is consistent with a large body of experimental data. It relies or recent spectroscopic models and on our interpretation of redistribution and electrical data, all of which indicate the existence of Cr complexes. The existence of rapidly diffusing interstitial Cr donors is assumed and justified. The model offers a unified picture of the effects of implantation on the Cr profile. It contains mechanisms for compensation and redistribution, which offer an explanation of the semi-insulating properties of Cr doped GaAs and of the two apparently incompatible classes of diffusion and anneal data. The redistribution depends on how the Cr was incorporated and on the vacancy concentration profiles. A study of representatives of the two classes of redistribution data allows us to estimate a lower limit of interstitial Cr diffusion constant and of the vacancy diffusion lengths in GaAs.