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High dose uranium ion implantation into silicon

Description: Implantation of uranium ions into silicon to a maximum dose of 6 x 10/sup 16/ atoms/cm/sup 2/, with a maximum concentration of 6 x 10/sup 21/ atoms/cm/sup 3/, has been carried out. This concentration corresponds to 12 at. % of uranium in the silicon host material. The implanted uranium content was measured by Rutherford backscattering and confirmed by a measurement of the alpha-particle activity of the buried uranium layer. The range and straggling of the uranium, and sputtering of the silicon target by uranium, were measured and are compared with theoretical estimates. The implantation was performed at an ion mean energy of 157 keV using a new kind of high current metal ion source.
Date: May 1, 1987
Creator: Brown, I.G.; Galvin, J.E. & Yu, K.M.
Partner: UNT Libraries Government Documents Department

Applications of Heavy-Ion Rutherford Backscattering Spectrometry (HIRBS) to the analysis of contact structures on GaAs and Ge

Description: The use of Heavy-Ion Rutherford Backscattering Spectrometry (HIRBS) for the analysis of layered structures on GaAs and Ge substrates has been studied. Direct comparisons of data obtained using both /sup 16/O and /sup 4/He projectiles for the characterization of contact structures have demonstrated the advantages of HIRBS for the study of substrates with increased atomic masses due to the improved mass resolution of the method for high Z materials. We present results obtained from a study of thermally induced interactions between Ga As and Ge substrates and the metals Pt and Pd. Results of the analysis of multiple layered structures on GaAs and GaAlAs substrate with HIRBS are also discussed.
Date: September 1, 1984
Creator: Yu, K.M.; Jaklevic, J.M. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

Plasma deposition of high temperature protective coatings

Description: Oxide ceramic films can be made using a vacuum arc based technique in which a metal plasma is formed in an oxygen background, with ion energy controlled by the application of a repetitive pulse bias to the substrate throughout the deposition. High ion energy early in the process produces atomic mixing at the film-substrate interface while lower but optimized ion energy later in the deposition can control the structure and morphology, and films that are adherent and dense can be formed in this way. In recent work we have investigated the formation of films of aluminum-silicon oxide on silicon carbide substrates by mixed aluminum and silicon plasmas produced from separate plasma sources. The Al to Si ratio was controlled by the plasma gun parameters, and the guns were pulsed simultaneously so as to mix the plasma streams before deposition; a magnetic multiple plasma homogenizer device was also used to further blend the two plasmas. Films with Al:Si ratios varying from 2:1 to 8:1 were produced in this study (Al:Si is 3:1 for Mullite), and the oxygen content in the films was controlled by varying the oxygen partial pressure during deposition. Additionally, we have compared some of the characteristics of alumina films plasma deposited on iron aluminide substrates with films produced by e-beam evaporation of Al{sub 2}O{sub 3} using oxygen ion beam assisted deposition onto unheated or heated substrates. Here we outline the film synthesis techniques and describe the characterization results obtained to-date.
Date: April 1, 1996
Creator: Monteiro, O.R.; Wang, Z. & Yu, K.M.
Partner: UNT Libraries Government Documents Department

Ion beam modification of the Y-Ba-Cu-O system with the MEVVA high current metal ion source

Description: We have used high-dose metal ion implantation to 'fine tune' the composition of Y-Ba-Cu-O thin films. The films were prepared by either of two rf sputtering systems. One system uses three modified Varian S-guns capable of sputtering various metal powder targets; the other uses reactive rf magnetron sputtering from a single-mixed-oxide stoichiometric solid target. Film thickness was typically in the range 2000--5000 A. Substrates of magnesium oxide, zirconia-buffered silicon, and strontium titanate have been used. Ion implantation was carried out using a metal vapor vacuum arc (MEVVA) high current metal ion source. Beam energy was 100--200 keV, average beam current about 1 mA, and dose up to about 10/sup 17/ ions/cm/sup 2/. Samples were annealed at 800--900/degree/C in wet oxygen. Film composition was determined using Rutherford Backscattering Spectrometry (RBS), and the resistivity versus temperature curves were obtained using a four-point probe method. We find that the zero-resistance temperature can be greatly increased after implantation and reannealing, and that the ion beam modification technique described here provides a powerful means for optimizing the thin film. 23 refs., 4 figs.
Date: March 1, 1989
Creator: Brown, I.G.; Rubin, M.D.; Yu, K.M.; Mutikainen, R. & Cheung, N.W.
Partner: UNT Libraries Government Documents Department

Photoluminescence spectroscopy and Rutherford backscattering channeling evaluation of various capping techniques for rapid thermal annealing of ion-implanted ZnSe

Description: We report on the effectiveness of proximity caps and PECVD Si{sub 3}N{sub 4}caps during annealing of implanted ZnSe films. OMVPE ZnSe films were grown using diisopropylselenide (DIPSe) and diethylzinc (DEZn) precursors, then ion-implanted with 1 {times} 10{sup 14} cm{sup {minus}2} N (33 keV) or Ne (45 keV) at room temperature and liquid nitrogen temperature, and rapid thermal annealed at temperatures between 200C and 850C. Rutherford backscattering spectrometry in the channeling orientation was used to investigate damage recovery, and photoluminescence spectroscopy was used to investigate crystal quality and the formation of point defects. Low temperature implants were found to have better luminescence properties than room temperature implants, and results show that annealing, time and temperature may be more important than capping material in determining the optical properties. Effects of various caps, implant and annealing temperature are discussed in terms of photoluminescence spectra.
Date: May 1, 1994
Creator: Allen, E. L.; Zach, F. X.; Yu, K. M. & Bourret, E. D.
Partner: UNT Libraries Government Documents Department

Fermi level stabilization energy in cadmium oxide

Description: We have studied the effects of high concentrations of native point defects on the electrical and optical properties of CdO. The defects were introduced by irradiation with high energy He+, Ne+, Ar+ and C+ ions. Increasing the irradiation damage with particles heavier than He+ increases the electron concentration until a saturation level of 5x1020 cm-3 is reached. In contrast, due to the ionic character and hence strong dynamic annealing of CdO, irradiation with much lighter He+ stabilizes the electron concentration at a much lower level of 1.7x1020 cm-3. A large shift of the optical absorption edge with increasing electron concentration in irradiated samples is explained by the Burstein-Moss shift corrected for electron-electron and electron-ion interactions. The saturation of the electron concentration and the optical absorption edge energy are consistent with a defect induced stabilization of the Fermi energy at 1 eV above the conduction band edge. The result is in a good agreement with previously determined Fermi level pinning energies on CdO surfaces. The results indicate that CdO shares many similarities with InN, as both materials exhibit extremely large electron affinities and an unprecedented propensity for n-type conductivity.
Date: April 8, 2010
Creator: Speaks, D. T.; Mayer, M. A.; Yu, K. M.; Mao, S. S.; Haller, E. E. & Walukiewicz, W.
Partner: UNT Libraries Government Documents Department

Engineering the Electronic Band Structure for Multiband Solar Cells

Description: Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.
Date: July 12, 2010
Creator: Lopez, N.; Reichertz, L. A.; Yu, K. M.; Campman, K. & Walukiewicz, W.
Partner: UNT Libraries Government Documents Department

Effects of structural defects on the activation of sulfur donors in GaN/x/As/1-x/ formed by N implantation

Description: The effects of structural defects on the electrical activity of S doped GaN{sub x}As{sub 1-x} layers formed by S and N coimplantation in GaAs are reported. S and N ions were implanted to the depth of about 0.4 {micro}m. Electrochemical capacitance voltage measurements on samples annealed at 945 C for 10s show that in a thin (<0.1 {micro}m) surface layer the concentration of active shallow donors is almost an order of magnitude larger in S and N co-implanted samples than in samples implanted with S alone. The activation efficiency of S donors also shows a broad minimum at a depth of about 0.2 {micro}m below the surface. The results of these electrical measurements are correlated with the distribution of structural defects revealed by transmission electron microscopy (TEM). The TEM micrographs show that in addition to a band of dislocation loops commonly found in ion implanted GaAs, an additional band of small voids is observed in samples co-implanted with S and N. The location of this band correlates well with the region of reduced electrical activation of S donors, suggesting that formation of the voids through N accumulation results in a lower concentration of active, substitutional N atoms.
Date: July 16, 2001
Creator: Jasinski, J.; Yu, K.M.; Walukiewicz, W.; Liliental-Weber, Z. & Washburn, J.
Partner: UNT Libraries Government Documents Department

Plasma synthesis of rare earth doped integrated optical waveguides

Description: We describe a novel means for the production of optically active planar waveguides. The makes use of a low energy plasma deposition. Cathodic-arc-produced metal plasmas the metallic components of the films and gases are added to form compound films. Here we discuss the synthesis of Al{sub 2{minus}x}ER{sub x}O{sub 3} thin films. The erbium concentration (x) can vary from 0 to 100% and the thickness of the film can be from Angstroms to microns. In such material, at high active center concentration (x=l% to 20%), erbium ions give rise to room temperature 1.53{mu}m emission which has minimum loss in silica-based optical fibers. With this technique, multilayer integrated planar waveguide structures can be grown, such as Al{sub 2}O{sub 3}/Al{sub 2{minus}x}Er{sub x}O{sub 3}/Al{sub 2}O{sub 3}/Si, for example.
Date: March 1, 1995
Creator: Raoux, S.; Anders, S.; Yu, K.M.; Brown, I.G. & Ivanov, I.C.
Partner: UNT Libraries Government Documents Department

In-situ deposition of sacrificial layers during ion implantation

Description: The retained dose of implanted ions is limited by sputtering. It is known that a sacrificial layer deposited prior to ion implantation can lead to an enhanced retained dose. However, a higher ion energy is required to obtain a similar implantation depth due to the stopping of ions in the sacrificial layer. It is desirable to have a sacrificial layer of only a few monolayers thickness which can be renewed after it has been sputtered away. We explain the concept and describe two examples: (i) metal ion implantation using simultaneously a vacuum arc ion source and filtered vacuum arc plasma sources, and (ii) Metal Plasma Immersion Ion Implantation and Deposition (MePIIID). In MePIIID, the target is immersed in a metal or carbon plasma and a negative, repetitively pulsed bias voltage is applied. Ions are implanted when the bias is applied while the sacrificial layer suffers sputtering. Low-energy thin film deposition - repair of the sacrificial layer -- occurs between bias pulses. No foreign atoms are incorporated into the target since the sacrificial film is made of the same ion species as used in the implantation phase.
Date: February 1, 1995
Creator: Anders, A.; Anders, S.; Brown, I. G. & Yu, K. M.
Partner: UNT Libraries Government Documents Department

The effect of co-implantation on the electrical activity of implanted carbon in GaAs

Description: We have undertaken a systematic study of the effect of co- implantation on the electrical properties of C implanted in GaAs. Two effects have been studied, the additional damage caused by co- implantation and the stoichiometry in the implanted layer. A series of co-implant ions were used: group III (B, Al, Ga), group V (N, P, As) and noble gases (Ar, Kr). Co-implantation of ions which create an amorphous layer was found to increase the electrical activity of C. Once damage was created, maintaining stoichiometric balance by co-implantation of a group III further increased the fraction of electrically active carbon impurities. Co-implantation of Ga and rapid thermal annealing at 950{degree}C for 10s resulted in carbon activation as high as 68%, the highest value ever reported.
Date: November 1, 1991
Creator: Moll, A.J.; Walukiewicz, W.; Yu, K.M.; Hansen, W.L. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

The effect of co-implantation on the electrical activity of implanted carbon in GaAs

Description: We have undertaken a systematic study of the effect of co- implantation on the electrical properties of C implanted in GaAs. Two effects have been studied, the additional damage caused by co- implantation and the stoichiometry in the implanted layer. A series of co-implant ions were used: group III (B, Al, Ga), group V (N, P, As) and noble gases (Ar, Kr). Co-implantation of ions which create an amorphous layer was found to increase the electrical activity of C. Once damage was created, maintaining stoichiometric balance by co-implantation of a group III further increased the fraction of electrically active carbon impurities. Co-implantation of Ga and rapid thermal annealing at 950{degree}C for 10s resulted in carbon activation as high as 68%, the highest value ever reported.
Date: November 1, 1991
Creator: Moll, A. J.; Walukiewicz, W.; Yu, K. M.; Hansen, W. L. & Haller, E. E.
Partner: UNT Libraries Government Documents Department

The effects of amorphous layer regrowth on carbon activation in GaAs and InP

Description: The effect of the Ga dose on the activation of implanted carbon in GaAs is determined. The free hole concentration is found to depend of the amorphous layer created by the Ga co-implant. Initial results on C implantation in InP indicate the behavior of C is very different in InP when compared to GaAs. The role of precipitation in reducing the activation of C in both GaAs and InP is discussed.
Date: November 1, 1993
Creator: Moll, A. J.; Haller, E. E.; Ager, J. W. III; Yu, K. M. & Walukiewicz, W.
Partner: UNT Libraries Government Documents Department

Mn l3,2 x-ray absorption spectroscopy and magnetic circulardichroism in ferromagnetic ga1-xmnxp

Description: We have measured the X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) at the Mn L{sub 3,2} edges in ferromagnetic Ga{sub 1-x}Mn{sub x}P films for 0.018 {le} x {le} 0.042. Large XMCD asymmetries at the L{sub 3} edge indicate significant spin-polarization of the density of states at the Fermi energy. The spectral shapes of the XAS and XMCD are nearly identical with those for Ga{sub 1-x}Mn{sub x}As indicating that the hybridization of Mn d states and anion p states is similar in the two materials. Finally, compensation with sulfur donors not only lowers the ferromagnetic Curie temperature but also reduces the spin polarization of the hole states.
Date: July 26, 2007
Creator: Stone, P.R.; Scarpulla, M.A.; Farshchi, R.; Sharp, I.D.; Beeman,J.W.; Yu, K.M. et al.
Partner: UNT Libraries Government Documents Department

Valence band anticrossing in GaBixAs1-x

Description: The optical properties of GaBixAs1-x (0.04< x< 0.08) grown by molecular beam epitaxy have been studied by photomodulated reflectance spectroscopy. The alloys exhibit a strong reduction in the bandgap as well as an increase in the spin-orbit splitting energy with increasing Bi concentration. These observations are explained by a valence band anticrossing model, which shows that a restructuring of the valence band occurs as the result of an anticrossing interaction between the extended states of the GaAs valence band and the resonant T2 states of the Bi atoms.
Date: July 11, 2007
Creator: Alberi, K.; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K. & Krotkus, A.
Partner: UNT Libraries Government Documents Department

Metal-insulator transition by isovalent anion substitution in Ga1-xMnxAs: Implications to ferromagnetism

Description: We have investigated the effect of partial isovalent anion substitution in Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only 2.4percent of As by P induces a metal-insulator transition at a constant Mn doping of x=0.046 while the replacement of 0.4 percent As with N results in the crossover from metal to insulator for x=0.037. This remarkable behavior is consistent with a scenario in which holes located within an impurity band are scattered by alloy disorder in the anion sublattice. The shorter mean free path of holes, which mediate ferromagnetism, reduces the Curie temperature TC from 113 K to 60 K (100 K to 65 K) upon the introduction of 3.1 percent P (1percent N) into the As sublattice.
Date: February 7, 2008
Creator: Stone, P. R.; Alberi, K.; Tardif, S. K. Z.; Beeman, J. W.; Yu, K. M.; Walukiewicz, W. et al.
Partner: UNT Libraries Government Documents Department

Non-magnetic compensation in ferromagnetic Ga1-xMnxAs and Ga1-xMnxP synthesized by ion implantation and pulsed-laser melting

Description: The electronic and magnetic effects of intentional compensation with non-magnetic donors are investigated in the ferromagnetic semiconductors Ga1-xMnxAs and Ga1-xMnxP synthesized using ion implantation and pulsed-laser melting (II-PLM). It is demonstrated that compensation with non-magnetic donors and MnI have similarqualitative effects on materials properties. With compensation TC decreases, resistivity increases, and stronger magnetoresistance and anomalous Hall effect attributed to skew scattering are observed. Ga1-xMnxAs can be controllably compensated with Te through a metal-insulator transition through which the magnetic and electrical properties vary continuously. The resistivity of insulating Ga1-xMnxAs:Te can be described by thermal activation to the mobility edge and simply-activated hopping transport. Ga1-xMnxP doped with S is insulating at all compositions but shows decreasing TC with compensation. The existence of a ferromagnetic insulating state in Ga1-xMnxAs:Te and Ga1-xMnxP:S having TCs of the same order as the uncompensated materials demonstrates that localized holes are effective at mediating ferromagnetism in ferromagnetic semiconductors through the percolation of ferromagnetic 'puddles' which at low temperatures.
Date: February 5, 2008
Creator: Scarpulla, M. A.; Stone, P. R.; Sharp, I. D.; Haller, E. E.; Dubon, O. D.; Beeman, J. W. et al.
Partner: UNT Libraries Government Documents Department

Fundamental Curie temperature limit in ferromagnetic Ga1-xMnxAs

Description: We provide unambiguous experimental evidence that the upper limit of {approx}110 K commonly observed for the Curie temperature TC of Ga{sub 1-x}Mn{sub x}As is caused by the Fermi-level-induced hole saturation. This conclusion is based on parallel studies of the location of Mn in the lattice, the effectiveness of acceptor center, and ferromagnetism on a series of Ga{sub 1-x-y}Mn{sub x}Be{sub y}As layers, in which the concentration of magnetic moments and of free holes can be independently controlled by the Mn and Be contents. Ion channeling and magnetization measurements show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of T{sub C} with increasing Be concentration. At the same time the free hole concentration remains relatively constant at {approx}5 x 10{sup 20}cm{sup -3}. These results indicate that the concentrations of free holes as well as of ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors. Based on these results, we propose to use heavy n-type counter-doping of Ga{sub 1-x}Mn{sub x}As (by, e.g., Te) to suppress the formation of Mn interstitials at high x, and thus improve the T{sub C} of the alloy system.
Date: September 24, 2002
Creator: Yu, K. M.; Walukiewicz, W.; Wojtowicz, T.; Lim, W. L.; Liu, X.; Bindley, U. et al.
Partner: UNT Libraries Government Documents Department

Mutual passivation effects in Si-doped diluted In{sub y}Ga{sub 1-y}As{sub 1-x}N{sub x} alloys

Description: We report systematic investigations of the mutual passivation effects of Si hydrogenic donors and isovalent nitrogen in dilute InGaAs{sub 1-x}N{sub x} alloys. Upon thermal annealing at temperatures above {approx}650 C, the Si atoms diffuse assisted by the formation and migration of Ga vacancies. When they find nitrogen atoms, they form stable Si{sub Ga}-N{sub As} nearest-neighbor pairs. As a result of the pair formation, the electrical activity of Si{sub Ga} donors is passivated. At the same time, the effect of an equal number of N{sub As} atoms is also deactivated. The passivation of the shallow donors and the N{sub As} atoms is manifested in a drastic reduction in the free electron concentration and, simultaneously, an increase in the fundamental band gap. Analytical calculations of the passivation process based on Ga vacancies mediated diffusion show good agreement with the experimental results. Monte Carlo simulations have also been performed for a comparison with these results. The effects of mutual passivation on the mobility of free electrons are quantitatively explained on the basis of the band anticrossing model. Optical properties of annealed Si-doped InGaAs{sub 1-x}N{sub x} samples are also discussed.
Date: July 21, 2003
Creator: Wu, J.; Yu, K.M.; Walukiewicz, W.; He, G.; Haller, E.E.; Mars, D.E. et al.
Partner: UNT Libraries Government Documents Department

Synthesis and optical properties of II-O-VI highly mismatched alloys

Description: We have synthesized ternary and quaternary diluted II-VI oxides using the combination of O ion implantation and pulsed laser melting. CdO{sub x}Te{sub 1-x} thin films with x up to 0.015, and the energy gap reduced by 150 meV were formed by O{sup +}-implantation in CdTe followed by pulsed laser melting. Quaternary Cd{sub 0.6}Mn{sub 0.4}O{sub x}Te{sub 1-x} and Zn{sub 0.88}Mn{sub 0.12}O{sub x}Te{sub 1-x} with mole fraction of incorporated O as high as 0.03 were also formed. The enhanced O incorporation in Mn-containing alloys is believed to be due to the formation of relatively strong Mn-O bonds. Optical transitions associated with the lower (E{sub -}) and upper (E{sub +}) conduction subbands resulting from the anticrossing interaction between the localized O states and the extended conduction states of the host are clearly observed in these quaternary diluted II-VI oxides. These alloys fulfill the criteria for a multiband semiconductor that has been proposed as a material for making high efficiency, single-junction solar cells.
Date: January 20, 2004
Creator: Yu, K.M.; Walukiewicz, W.; Shan, W.; Wu, J.; Beeman, J.W.; Scarpulla, M.A. et al.
Partner: UNT Libraries Government Documents Department

Pressure-dependent photoluminescence study of ZnO nanowires

Description: The pressure dependence of the photoluminescence (PL) transition associated with the fundamental band gap of ZnO nanowires has been studied at pressures up to 15 GPa. ZnO nanowires are found to have a higher structural phase transition pressure around 12 GPa as compared to 9.0 GPa for bulk ZnO. The pressure-induced energy shift of the near band-edge luminescence emission yields a linear pressure coefficient of 29.6 meV/GPa with a small sublinear term of -0.43 meV/GPa{sup 2}. An effective hydrostatic deformation potential -3.97 eV for the direct band gap of the ZnO nanowires is derived from the result.
Date: September 13, 2004
Creator: Shan, W.; Walukiewicz, W.; Ager III, J.W.; Yu, K.M.; Zhang, Y.; Mao, S.S. et al.
Partner: UNT Libraries Government Documents Department