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A thermal gradient technique was used to grow GaP crystals at ~1040~ from gallium solutions doped with zinc, sulfur, selenium, or tellurium. The solid solubilities of the donor impurities appear to vary linearly with the melt concentrations at the lower doping levels and with the square root of the melt concentration at higher doping levels, all in the extrinsic range. This behavior contrasts with that of zinc, for which the solid solubility varies only as the square root of the melt concentration as expected for a singly ionized acceptor dissolving in an extrinsic semiconductor. The excess donor or acceptor concentrations were significantly lower than the impurity concentrations at the higher doping levels.In an earlier paper (1) we discussed the solid solubility and electrical behavior of tin, an amphoteric group IV impurity, in GaP. In this paper we present the results of similar studies on GaP crystals grown from gallium solutions containing the group VI donors sulfur, selenium, or tellurium or the group II acceptor zinc. Of particular interest here is the variation of doping level and electrical activity as a function of impurity concentration in the liquid at constant temperature. We shall see that, while the behavior of zinc is relatively simple, the donor behavior does not appear to be completely consistent with models previously suggested for the incorporation of group VI impurities in III-V compounds. ExperimentalThe crystals were grown from gallium solutions contained in sealed, evacuated vitreous silica tubes by using a thermal gradient method described previously (1, 2). Seventeen crystals were grown at 1040 ~ _+ 20~ in a single run lasting five weeks. The thermal gradient in the furnace was ~15 to 20 deg/cm. Large grained polycrystalline ingots weighing about 2g were obtained.Values of IND--NAI, the excess donor or acceptor concentration, were obtained from surface barrier capacitance measurements as described previously (1, 3). As will be evident from the results, the agreement between duplicate capacitance measurements on different parts of the crystals varied considerably from crystal to crystal, presumably due to variations in the quality of the crystal (freedom from micro-occlusions, grain boundaries, etc.). In seeking evidence of precipitation of the dissolved impurities some samples were heated to ~1000~ for periods of 1-8 min and then quenched either in a jet of nitrogen or in a silicone oil. After etching to avoid any surface effects the samples were remeasured.The impurity concentrations were determined by using spectrophotometric techniques. Prior to analysis the samples were crushed and digested for a day or more in hot concentrated hydrochloric acid to insure removal of any occluded gallium or other phases containing the impurity in question. The tellurium-and selenium-doped samples were also digested briefly (~5 to 15 min) in aqua regia. Rods were cut from ten samples (doped with zinc, selenium, or tellurium) for mass spectroscopic analysis. The principal contaminant was found to be si...

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Shifts in the potential of maximum adsorption with coverage, particularly on platinum, indicate some ~r-bonding of naphthalene with that metal. Naphthalene adsorbs parallel to the surface on Pt (close to maximum coverage for that orientation) and probably on Ni and Fe but must adsorb perpendicular to the surface on Cu, since coverages of more than a monolayer must otherwise be assumed.The free energy of adsorption of naphthalene was calculated for each system. It was found to be roughly constant for all metals but with a slightly higher value for platinum. This suggests that the amount of adsorption is determined mainly by the difference between the dispersive interaction with the metal of organic and water (3), with some ~r-bonding on platinum.No significant lateral interactions between adsorbed molecules were observed.