K.B. Wolfstirn

Variation of Electrical Properties with Zn Concentration in GaP

The resistivity and Hall coefficient RH for Zn‐doped GaP were measured at temperatures between 4.2° and 775°K. Neutron activation and through diffusion with radioactive 65Zn were used to determine the Zn concentration NZn, which ranged from 6.7×1016 cm−3 to 2.1×1019 cm−3. At the lowest Zn concentration the thermal ionization energy for Zn in GaP was found to be 0.060±0.002 eV. The thermal ionization energy decreases rapidly for Zn concentrations in excess of 2.0×1017 cm−3. Metallic impurity conduction was observed at a Zn concentration of 2.1×1019 cm−3. The low‐concentration region is observed for NZn≲2.0×1017 cm−3, the intermediate‐concentration region for 2.0×1017≲NZn≲2.1×1019 cm−3, and the high‐concentration region for NZn≳2.1×1019 cm−3. In the intermediate‐concentration region the high‐temperature hole concentration, determined from p=1/eRH, was found to exceed the Zn concentration by a significant amount. Analysis of the temperature‐dependent hole concentration results in an effective density‐of‐stat...

Influence of surface band bending on the incorporation of impurities in semiconductors: Te in GaAs

Abstract A portion of the 1000°C solid solubility isotherm for Te in GaAs was determined by liquid-phase epitaxial growth of layers doped with radioactive 129 m Te. The Te concentration in the solid was varied from 2 × 10 17 to 4 × 10 19 atoms/cm 3 and was found to depend linearly on the Te atom fraction in the liquid phase. For a linear dependence, a distribution coefficient of 0·35 may be assigned to Te at 1000°C. For extrinsic conditions and dilute liquid solutions, present models for the incorporation of fully ionized impurities, which do not include surface band bending, lead to a square-root dependence of the impurity concentration in the solid on the impurity concentration in the liquid phase. Treatment of the liquid-solid interface as a metal-semiconductor Schottky barrier gives an electron concentration at the semiconductor surface which is independent of the impurity concentration in the solid, and results in a linear relationship between the concentration in the solid and liquid phase. Existing results for other impurities in GaAs and GaP suggest that it is necessary to consider surface band bending in the interpretation of other impurity III-V semiconductor systems.

Hole and electron mobilities in doped silicon from radiochemical and conductivity measurements

Abstract Room temperature (300°K) conductivity mobilities of holes and electrons in Ga, As, and Sb doped silicon have been calculated from electrical and radiochemical measurements using the effective mass approximation. The concentration range investigated was from 1016 to 2 × 1018 cm−3 and from 4 × 1015 to 2.5 × 1019 cm−3 for p− and n−type silicon respectively. lonization energies from Hall effect measurements and their changes with concentration are estimated for the nondegenerate specimens. lonization is assumed to be complete in the degenerate cases. In addition, the results are compared with published drift, conductivity and Hall mobilities.

Distribution Coefficient of Germanium in Gallium Arsenide Crystals Grown from Gallium Solutions

Gallium arsenide crystals doped with germanium were grown from gallium solutions at 900°–875°C. The Ge concentration in the liquid was varied from 0.004 to 56 at.%, and the Ge concentration in the GaAs crystals determined using radiotracer and other techniques. The Ge concentration in the solid varied linearly with increasing Ge concentration in the liquid up to 5 at.% and kGe = (Ges)/(Gel)=0.0083±0.001. Above 5‐at.% Ge in the growth solution, kGe increased. At low doping levels Ge acts predominantly as a simple acceptor substituting on arsenic sites. At high doping levels, in the extrinsic range, the Ge concentration in the solid is considerably greater than the free carrier concentration. The form in which the excess Ge exists is not known.

Reactions of group iii acceptors with oxygen in silicon crystals

Abstract Hall effect and conductivity results are presented on Si crystals containing from 5 × 10 17 to 1.6 × 10 18 cm −3 of oxygen and various dopings of B, Al and Ga before and after reaction at various temperatures (410–1350°C). Evidence in support of the tetrahedral SiO 4 model for the donor formed from oxygen suggested by Kaiser is presented. A large hole-electron effect is noted in the presence of excess acceptor concentration. In addition, specific interactions with the acceptor atoms occur. Although the reactions are complex and are not understood, three kinds are postulated in order to account for the results : (1) The formation of isolated SiO 4 donors such as occurs in undoped Si crystals containing oxygen. (2) The reaction of oxygen at an acceptor atom to form a neutral compound or a “molecular pair”. (3) The formation of a donor involving eight oxygen atoms and an acceptor atom. The latter reaction is believed to occur most readily in the case of Al-doped crystals and, in an excess of oxygen, leads to the formation of one donor per Al atom.

Hall‐Effect Levels Produced in Te‐Doped GaAs Crystals by Cu Diffusion

Hall‐effect measurements have been made on Te‐doped GaAs crystals diffused with known amounts of 64Cu sufficient to convert the crystals to p‐type. Energy levels are found above the valence band at 0.123±0.005 eV, 0.145±0.005 eV, 0.166±0.005 eV, 0.19±0.005 eV, and 0.43±0.01 eV. An analysis of the Hall data has been made by means of computer programs. The results may be summarized as follows: (1) Ga vacancies produced during the Cu diffusion associate with and neutralize Te as a compensating center. (2) The ionization energy of the TeCuGa pair is 0.19 eV rather than 0.166 eV as suggested previously.

Investigation of quenched-in defects in Ge and Si by means of 64Cu

Abstract Quenched-in defects in Ge have been investigated by comparing the hole cones, produced by the acceptor defects with 64Cu cones, resulting when 64Cu is diffused into them at 500°C. It is found that for low defect cones. (~5 × 1014 cm−3) one 64Cu is added per defect hole whereas for higher cones. (>1015 cm−3) more than one 64Cu is added. This result is interpreted as support for the defect cluster model of Letaw. Further support for this model is provided by a study of the kinetics of loss of the defect acceptors on annealing. Ge, quenched in the presence of 3 × 1016 cm−3 64Cu, is found to add up to 5 × 1015 cm−3 64Cu of the same vintage at 500°C. This result is interpreted as supporting the clustering mechanism of vacancy precipitation. Peculiarities in the kinetics of precipitation of Cu from Ge are likewise able to be understood on this model. The cone, of ~4 × 1015 cm−3 vacancies found by tweet as present in as-grown Ge crystals at the m.p. has been verified. Results similar to those discussed above for Ge are reported for Si.

Defect Centers in GaAs Produced by Cu Diffusion

Evidence for defect centers having an ionization energy at Ev+0.10 eV in melt‐grown GaAs is given based on: (1) Hall‐effect measurements on Cu‐diffused crystals. (2) Residual 64Cu left in GaAs after extraction by indium. (3) Decrease in electron concentration of donor‐doped crystals after annealing. The failure to observe the defect level in photoluminescence is discussed. The results suggest that Ga vacancies are present in clusters in melt‐grown GaAs crystals.

Shallow acceptor level in GaAs crystals resulting from Cu diffusion

Abstract The shallow acceptor level at 0.021 eV observed by W helan [ J. Appl. Phys. 31 , 1507 (1960)] by introducing Cu at high temperatures (∼1000°C) and annealing at lower temperatures (∼ 500°C) has been investigated further. We have established that the acceptor requires the presence of Cu for its formation and then only when the Cu is introduced above ∼ 750°C. The net acceptor conc. is found to increase with the initial Cu conc. and to decrease with an increase in the final annealing temperature. Consideration of the stability properties of the acceptor indicates that Cu-donor pairs as well as the Ga-vacancy are unlikely choices for the acceptor. Calculations of the minority donor conc. suggest that changes in the net acceptor conc. are caused, at least in part, by changes in a donor impurity, possibly oxygen. In addition, the possibility is discussed that the net acceptor conc. changes, as well as the minority donor conc. changes are the result of transfer between III-V sites of C or Si impurities.

Evidence for a primarily nonradiative Si,O defect in GaP

Experimental evidence is presented to establish the existence of a Si,O defect impurity system in GaP. This defect is shown to be a strong nonradiative recombination center in n‐type material. A photoluminescence band near 1.55 eV at room temperature has been associated with the Si,O defect.