Nuclear Instruments and Methods最新文献

The fabrication of cathode doping notches in GaAs Gunn material by use of ion implantation has been investigated. Two techniques were studied: Epitaxial GaAs having an n⁺-n-n²⁺ structure was implanted with either p-type dopant, magnetium ions, or compensating oxygen ions. Alternatively Gunn material, without an n⁺ contact layer, was implanted with both n-type dopant selenium ions and p-type magnesium ions to form the cathode-notch configuration. In both cases annealing was carried out in an arsenic vapour overpressure. It is found that the magnitude of notches produced is governed by the extent to which impurity diffusion takes place during post-implant annealing.

A model including precipitate dissolution and solute segregation is used to explain the changes in precipitate distribution during 100 keV Al⁺ ion irradiation of AlGe alloy. It is found by TEM that Ge precipitates in the peak damage region i.e. <100 nm from the surface are destroyed by prolonged irradiation to doses greater than 28 dpa, whereas precipitates near the tail of the damage profile i.e. 100–250 nm from the surface, continue to grow. SIMS has shown that the dissolution of near-surface precipitates is accompanied by segregation of Ge to depths below the damage peak, indicating that Ge segregates down defect gradients.

The results show that solute segregation is an important factor in determining precipitate stability. It is thought that the reversal in precipitate behaviour from growth to dissolution occurs because the solute depletion in the matrix near the surface reduces the solute arrival rate at the precipitate sufficiently for recoil dissolution to determine the precipitate behaviour. A preliminary study on low temperature irradiation of AlGe shows that Ge solute re-distribution rate is limited by the concentration and mobility of vacancy-solute complexes, and not by the rate of precipitate dissolution.

Results are presented of work using transmission electron microscopy to examine the evolution of the structure related to the absence of new blisters after high fluence He bombardment of Nb. At 500°C, the mean bubble diameter increases from 3.2 nm at 1.9 × 10¹⁷ He cm⁻² (fluence smaller than the blistering threshold) to 9.7 nm at 9.4 × 10¹⁸ He cm⁻² (fluence larger than the fluence necessary for the sputtering of the blisters). This increase is done at the expense of the bubble density which decreases from 5.5 × 10¹² cm⁻² to 2.8 × 10¹¹ cm⁻². However it is remarkable that the total volume of bubbles remains constant. Due to He saturation in the implanted layer the pressure is constant. It is shown that the diameter increase and density decrease mean a lowering of the stresses in the membranes between bubbles, thus preventing the formation of new blisters. This suggests that large bubbles can continue to grow, without becoming overpressurized, by absorbing mostly radiation-produced vacancies whereas small bubbles shrink by absorbing mostly interstials and releasing He through radiation assisted diffusion.

This paper describes a fast method to calculate the implantation parameters (φ, E) required in order to obtain a given concentration profile after annealing and driven-in diffusion (C_s, C_b, x_j) for thick junctions xx_j > 10h, where h = 2R_p). The method is usable for final Gaussian concentration profiles peaked at the SiO₂/Si interface or at the substrate surface and can be employed for bipolar transistors and buried layers in IC technology.

This investigation is part of an ongoing research project directed at applying the techniques of ion implantation doping and ion scattering analysis to identify the mechanisms associated with the anodic dissolution of TiPt alloys. The TiPt alloys produced by ion implantation were electrochemically examined in hydrogen-saturated 1N H₂SO₄ by both potentiostatic polarization and open-circuit potential methods. In this study, Ti samples implanted to relatively high doses (5.4 × 10¹⁵ −2.9 × 10¹⁶ atoms/cm²) were examined by ion scattering analysis at various stages in the electrochemical measurements. Quantitative measurements showed that the majority of the implanted Pt accumulated on the surface during anodic dissolution and underwent large scale surface migration. Evidence is also presented for the transition of the Pt on the surface from a catalytically “active” to “inactive” state. Possible mechanisms for the observed catalytically “inactive” Pt are discussed.

The electrochemical behaviour and pitting corrosion resistance of ARMCO iron specimens implanted with nitrogen or boron ions have been studied.

The electrochemical measurements were performed in different solutions in order to characterize material behaviour under most usual work conditions. The following solutions were employed, (a) 0.5M H₂SO₄ deaerated solution, to study the active corrosion; (b) 0.15N H₃BO₃ + 0.15N Na₂B₄O₇ · 10 H₂O, pH 8.5, to study the passivating condition; (c) solution (b) + 2400 p.p.m. of Cl⁻ to study the passivity breakdown; (d) 1M NaCl, pH 4, to study the pitting corrosion.

The implantation affects the anodic dissolution of iron, lowering the intergranular attack and enhancing the protective capacity of the oxide layers, modifying the pit nucleation and growth.

Scanning Electron Microscopy (SEM) was used in order to study the surface morphology.

Zinc implantation has been carried out in n-type GaP at an energy of 100 keV and at doses of 10¹³−10¹⁶ cm⁻². Hall-effect and sheet-resistivity measurements combined with an anodic oxide growth and layer stripping technique have been employed to determine doping profiles in Zn-implanted layers. The effects of implant dose and temperature, annealing time, and encapsulating material on doping profiles formed have been investigated. It has been shown that various doping profiles are formed depending upon implant dose and annealing time, due to the redistribution of implanted Zn which is influenced by these implantation parameters. Very shallow p-type layers (∼1000 Å thick) have been formed by a 2 min annealing at 900°C. Photodetectors with the maximum quantum efficiency of 44% at a wavelength of 440 nm have been fabricated by using the shallow p-type layers formed in n-type GaP substrate.

The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate ⪅5 at% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH₁) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter-deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon are discussed relative to the different models proposed for amorphous silicon.