As an acceptor dopant with a solid:liquid distribution coefficient ks<1, iron is an example of an impurity which can be used in modest amounts to ensure that an adequate fraction of EL2 midgap defects are ionized along the length of a melt-grown GaAs crystal, as desired for semi-insulating behavior. The results of such deliberate doping with iron (when NFe is in the mid-1015 cm−3 range) are reported for crystals grown by both the liquid encapsulated Czochralski and the vertical gradient freeze methods. Except in the very tail region of such crystals (when NFe≳NEL2 and high resistivity p-type behavior results), GaAs with this modest iron modification to the compensation balance behaves with quite ordinary semi-insulating properties. The iron acceptors are then all ionized, and are optically ‘‘invisible.’’

Optical and electrical properties are described for bulk GaAs, grown from a melt doped with iron to create FeGa deep acceptors in a sufficient amount (exceeding the EL2 defect concentration) to make high-resistivity p-type rather than semi-insulating material. Both iron photoionization and EL2+ photoneutralization contribute to the near-infrared optical absorption. This made it possible to deduce the concentrations (NAi and NAn) of ionized and lattice-neutral iron, and the ratio (NAi/NAn). Temperature dependent measurements of dc electrical transport yielded quantities such as the free hole density, and hence the Fermi energy, for the 290–420 K range. This information combined with (NAi/NAn) led to a determination of the iron acceptor’s free energy εA(T): about 0.46 eV above the valence band at 300 K, and ∼40 meV closer at 420 K. The temperature dependence of εA for iron is shown to differ from εv, εc, midgap, or the free energy for CrGa acceptors in GaAs.

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Silver halide crystals of composition AgC10 95Br.0 05 were extruded to form infrared transmitting fibers of 0.9 mm diameter and 1.5 meters in length. Microscopic examination reveals an initial fine grain structure with a grain size of the order of 1 pm. Thermal treatment at 200 °C following extrusion results in rapid grain growth.Infrared spectral transmission measurements of the fibers show absorption features at 3 -3.2 pm, 6.1 pm and 12 -13 pm attributed to water and bands at 6.8 and 7.1 pm attributed to COI molecules. These features are superimposed on a scatter loss which has a a -2 dependence.Transmission measurements at 10.6 pm with a CO2 laser show a linear dependence of power output on power input for levels from 1 to 20 watts incident on the fiber face.For a variety of power input geometries, the power output distribution was independent of the input conditions. * currently a visiting professor at Abstract Silver halide crystals of composition AgCl^^^Br.^^^ were extruded to form infrared transmitting fibers of 0.9 mm diameter and 1.5 meters in length. Microscopic examination reveals an initial fine grain structure with a grain size of the order of 1 ym. Thermal treatment at 200°C following extrusion results in rapid grain growth. Infrared spectral transmission measurements of the fibers show absorption features at 3-3.2 ym, 6.1 ym and 12-13 ym attributed to water and bands at 6.8 and 7.1 ym attributed to COJ molecules. These features are superimposed on a scatter loss which has a X~^ dependence. Transmission measurements at 10.6 ym with a C02 laser show a linear dependence of power output on power input for levels from 1 to 20 watts incident on the fiber face. For a variety of power input geometries, the power output distribution was independent of the input conditions.

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