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Notes: High-energy Ti+ ions ranging from 1 to 5 MeV were implanted into p-type InP:Zn (for two different zinc concentrations) at both room temperature and 200 °C. The range statistics for Ti implanted at various energies were calculated by analyzing the as-implanted profiles determined by secondary-ion mass spectrometry. Ti did not redistribute during post-implantation annealing except for a slight indiffusion, irrespective of the implant or annealing temperatures used. This behavior is different from the behavior of other implanted transition metals (Fe and Co) in InP, which redistributed highly when the implants were performed at room temperature. In the MeV Ti-implanted InP:Zn the background Zn showed a small degree of redistribution. Rutherford backscattering measurements showed a near virgin lattice perfection for 200 °C implants after annealing. Buried layers with intrinsic resistivity were obtained by MeV Ti implantation in InP:Zn (p=5×1016 cm−3).

Notes: High energy B implantations were performed into n-type GaAs and InP at room temperature in the range of energies from 1 to 5 MeV and fluences from 1011 to 1016 cm−2. The material did not become amorphous for any of the fluences used. Buried layers with resistivities as high as 108 Ω cm and 106 Ω cm were obtained in GaAs and InP, respectively, after heat treatments. The breakdown voltages corresponding to the highest resistivities are 80 and 35 V, respectively, in GaAs and InP. In GaAs, the Rutherford backscattering analysis on the annealed samples showed an aligned yield close to that of a virgin sample, whereas, the yield in InP is more than that of the as-implanted sample.

Notes: We have theoretically and experimentally analyzed the laser-induced evaporation process for deposition of superconducting thin films from bulk targets. The spatial thickness variations have been found to be significantly different from a conventional thermal deposition process. Unlike a cos θ thickness variation expected from a thermal evaporation process, the laser evaporation process is characterized by a forward-directed deposit with a sharp variation in its thickness as a function of distance from the center of the deposit. We have studied in detail the interactions of nanosecond excimer laser pulses with bulk YBa2Cu3O7 targets leading to evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating the pulsed laser evaporation (PLE) process has been developed. This model considers an anisotropic three-dimensional expansion of the laser-generated plasma, initially at high temperature and pressure. The forward-directed nature of laser deposition has been found to result from anisotropic expansion velocities of the plasma edges arising due to the density gradients in the gaseous plasma.The physical process of the laser ablation technique for deposition of thin films can be classified into three separate interaction regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation and initial isothermal expansion, and (iii) adiabatic expansion leading to deposition of thin films. The first two regimes occur during the time interval of the laser pulse, while the last regime initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is nonthermal as a result of interaction of the laser beam with the evaporated material. The expansion velocities of the plasma edges are related to the initial dimensions and temperature of the plasma, and the atomic weight of the respective species present in it. Preliminary calculations have been carried out on spatial thickness variations as a function of various parameters in PLE deposited thin films. The effects of the various beam and substrate parameters including energy density and substrate-target distance affecting the nature of deposition of superconducting thin films have been theoretically examined. Experimental results have been obtained from thin films deposited on silicon substrates by XeCl pulsed excimer laser (λ=308 nm, τ=45×10−9 s) irradiation. The spatial thickness and compositional variations in thin films have been determined using Rutherford backscattering technique and the results compared with the theoretical calculations.

Notes: High-energy Fe and Co implantations were performed into InP:Sn at room temperature and 200 °C in the energy range 0.34–5.0 MeV. Range statistics were calculated for these ions in the above energy range. For the room-temperature implants, implant redistribution peaks around 0.8Rp and Rp+ΔRp, and both in- and out-diffusion of the implant are observed in the secondary-ion-mass-spectroscopy profiles of the annealed samples. The implant redistribution present in the room-temperature implants is much different than in elevated-temperature implants. For buried (high-energy) implants, much of the implant diffusion is eliminated if the implants are performed at 200 °C. For 200 °C implants, the yield of the Rutherford backscattering spectra on the annealed samples is close to that of a virgin sample. The MeV energy Fe and Co implantations at 200 °C are useful to obtain thermally stable, buried, and high-resistance layers of good crystalline quality in n-type InP and for the compensation of the tail of the buried n-type implant. However, due to the low solubility of Fe and Co in InP, the implants of these species are useful only to compensate n-type carriers with concentrations below 1017 cm−3.

Notes: Variable-fluence 3-MeV Si+ and 150-keV Ge+ implants were performed into InP:Fe at 200 °C. Lattice damage in the material is greatly reduced over comparable room-temperature (RT) implantations and is rather insensitive to fluence for Si+ implantation in the range of 8 × 1014–5 × 1015 cm−2, and no amorphization occurs. For 8 × 1014-cm−2 Si+ implantation at 200 °C, the dopant activation is 82% and carrier mobility is 1200 cm2/V s after 875 °C/10-s annealing, whereas for the RT implantation the corresponding values are 48% and 765 cm2/V s, respectively. The reasons for the improved mobility in the elevated-temperature implants were investigated using Rutherford-backscattering spectrometry. At a dose of 8 × 1014 cm−2, the aligned yield after annealing is close to that of a virgin sample, indicating a low concentration of residual damage in the 200 °C implant, whereas the lattice remained highly defective in the RT implanted sample. Elevated-temperature implantation of Si+ and Pi+ ions was also investigated. Coimplantation did yield an improvement in activation for an implanted fluence of 2 × 1015 cm−2 Si+, but resulted in an inferior lattice quality which degraded the carrier mobility compared to a Si+ (only) implant. For a 1 × 1014-cm−2 Ge+ implant, the maximum dopant activation is 50% (donor) and the material did not turn p type even after 925 °C annealing.

Notes: Single-energy Fe implantation at energies in the range 50 keV–2 MeV to achieve a peak Fe concentration of 1–2×1018 cm−3 is performed into undoped (n-type) InGaAs layers grown on InP:Fe. The first four statistical moments of the Fe profiles measured by secondary-ion mass spectrometry are determined. The Pearson IV distribution calculated from these moments matches the implant-profile closely. Samples implanted with Fe to doses in the range 5x1012 –2×1015 cm−2 at 380 keV are analyzed by Rutherford backscattering measurements to study ion-induced damage. For 380-keV implants, amorphization begins at a dose of ≈3×1013cm−2.

Notes: The damage formed by 1.25 MeV, self-ions in Si at liquid nitrogen temperature was studied. A dominant feature of the damage for moderate ion fluences is the presence of isolated amorphous regions over the range of the ions. The microstructure of this damage is detailed and formation mechanisms discussed. The amorphous regions are shown to give rise to strain in the surrounding crystal lattice which varies with ion dose in a complicated manner. The annealing behavior of the damage was studied and two distinct, low-temperature stages observed. Different mechanisms are shown to be responsible for each stage including a transient mechanism at 300 °C initiated by the release of defects from damage clusters, and enhanced crystallization of amorphous Si at 400 °C due to lattice stress.

Notes: Vacancy-type defects produced by implantation of MeV doses of Si ions (1011–1015 atoms/cm2) at room temperature have been probed using depth-resolved positron annihilation spectroscopy. The defect (divacancy) concentration increases linearly with dose for low doses (〈1012 Si/cm2). In situ isochronal annealing was followed for oxygen-containing Si (10 ppm) and oxygen-"free'' Si implanted to doses (5×1012 and 5×1014 Si/cm2). Two main annealing stages were observed at the same temperatures in the studied samples in spite of significant differences in doses and oxygen content. In the first stage (∼200 °C) a significant fraction of divacancies was observed to form large vacancy clusters. These clusters were removed in the second stage (∼675 °C) after which the oxygen-free samples returned to pre-irradiation conditions, whereas oxygen-defect complexes were formed in the oxygen-containing samples.

Notes: Raman scattering and ion channeling techniques were used to investigate the damage in GaAs implanted at room temperature with 100-keV Si+ ions. The ion-induced damage was analyzed for different ion doses and dose rates (current densities). The development of different damage components was monitored by comparing a Raman signal which is specific to amorphization in GaAs to ion channeling results which are sensitive to small-volume crystalline defects, as well as to amorphous regions. Raman analysis showed that the rate of growth of the amorphous fraction with implant dose was comparable to the growth rate of the total damage as determined by ion channeling. However, while Raman analysis indicated a weak dependence of damage on dose rate, the ion channeling results showed a substantially stronger dependence. These results demonstrate that the damage morphology in GaAs is dependent upon both dose and dose rate, and that the dose-rate-dependent component of the total damage consists primarily of crystalline defects.

Notes: Low (keV) and high (MeV) energy Al and B implants were performed into n-type 6H- and 3C-SiC at both room temperature and 850 °C. The material was annealed at 1100, 1200, or 1400 °C for 10 min and characterized by secondary ion mass spectrometry, Rutherford backscattering (RBS), photoluminescence, Hall and capacitance-voltage measurement techniques. For both Al and B implants, the implant species was gettered at 0.7 Rp (where Rp is the projected range) in samples implanted at 850 °C and annealed at 1400 °C. In the samples that were amorphized by the room temperature implantation, a distinct damage peak remained in the RBS spectrum even after 1400 °C annealing. For the samples implanted at 850 °C, which were not amorphized, the damage peak disappeared after 1400 °C annealing. P-type conduction is observed only in samples implanted by Al at 850 °C and annealed at 1400 °C in Ar, with 1% dopant electrical activation. © 1995 American Institute of Physics.