The preparation of Fe-doped and nominally undoped semi-insulating InP

Nominally undoped semi-insulating (SI) InP (p approximately=10/sup 7/ Omega cm) was prepared by annealing of InP wafers in a phosphorus atmosphere. The electronic transport properties are compared to those of Fe-doped (SI) InP crystals grown by the liquid-encapsulated-Czochralski (LEC) technique. The values of the electron mobility of the undoped SI material are considerably higher than those of the Fe-doped and are close to the theoretical values of undoped InP. Depth profiles of the carrier concentration show a strong variation within the first 20 mu m, which can be fitted by the literature data of the diffusion coefficients of P and In, but the bulk SI behavior of the samples cannot be explained by self-diffusion mechanisms. The position of the energy level of the deep acceptor is found to lie 0.67+or-0.02 eV below the edge of the conduction band. Although this value is close to that of Fe/sup 3+/2+/ the results of chemical analysis make it unlikely that Fe is the acceptor.<>