MELT-GROWN P-TYPE GAAS WITH IRON DOPING

Optical and electrical properties are described for bulk GaAs, grown f rom a melt doped with iron to create Fe(Ga) deep acceptors in a suffic ient amount (exceeding the EL2 defect concentration) to make high-resi stivity p-type rather than semi-insulating material. Both iron photoio nization and EL2+ photoneutralization contribute to the near-infrared optical absorption. This made it possible to deduce the concentrations (N(Ai) and N(An)) of ionized and lattice-neutral iron, and the ratio (N(Ai)/N(An)). Temperature dependent measurements of dc electrical tra nsport yielded quantities such as the free hole density, and hence the Fermi energy, for the 290-420 K range. This information combined with (N(Ai)/N(An)) led to a determination of the iron acceptor's free ener gy epsilon(A) (T): about 0.46 eV above the valence band at 300 K, and approximately 40 meV closer at 420 K. The temperature dependence of ep silon(A) for iron is shown to differ from epsilon(v), epsilon(c), midg ap, or the free energy for Cr(Ga) acceptors in GaAs.