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The influence of SiO2 and SiNx cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750°C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20?ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900°C. However, in this case, Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiOx grown during annealing which only can be avoided by the usage of SiNx cover layers. [ABSTRACT FROM AUTHOR]

Heavily p-type doped Ge layers were fabricated by 100 keV Ga implantation and subsequent flash lamp annealing for 3 ms in the temperature range between 700 and 900 °C. For comparison, some samples were annealed in a rapid thermal processor for 60 s. Ga fluences of 2×1015, 6×1015, and 2×1016 cm-2 were chosen in order to achieve Ga peak concentrations ranging from values slightly below the equilibrium solid solubility limit of 4.9×1020 cm-3 up to 3.5×1021 cm-3 which corresponds to a maximum Ga content of about 8 at. %. The structure of the doped layer and the Ga distribution were investigated by Rutherford backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy, and secondary ion mass spectrometry. Temperature dependent Hall effect measurements were carried out in order to determine the electrical properties of the Ga-doped Ge layers. It is shown that by flash lamp annealing Ga diffusion into the bulk can be completely avoided and the Ga loss by outdiffusion from the surface is reduced. The lowest sheet resistance of 36 Ω/sq. was achieved for the medium Ga concentration annealed at 900 °C. The best Ga activation values are 73%, 60%, and 24% for the three Ga fluences under investigation. The Ga activation is correlated with the layer regrowth. Incomplete epitaxial regrowth as observed in some samples leads to lower activation. [ABSTRACT FROM AUTHOR]

The electrical properties of heavily Al doped single and nanocrystalline 4H–SiC layers on semi-insulating 4H–SiC substrate, prepared by multienergy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. Ion beam induced crystallization is used to prepare the nanocrystalline SiC layers. The doping levels are chosen around the solid solubility limit of 2×1020 cm-3 in the range from 5×1019 to 1.5×1021 cm-3. The comparison of the results shows that heavily Al doped single crystalline SiC layers have superior conduction properties. The lowest resistivities measured at room temperature are 0.08 and 0.8 Ω cm for the single crystalline and nanocrystalline samples, respectively. Recent results on enhanced Al acceptor activation in nanocrystalline SiC cannot be confirmed. There is an upper limit for the hole concentration in the nanocrystalline samples independent of the Al supersaturation level in the as-implanted state due to outdiffusion of Al in excess to the solid solubility limit during annealing. In contrast to the nanocrystalline SiC layers the as-implanted Al profile in single crystalline material remains stable after annealing even for concentrations above the solid solubility limit. Therefore, in single crystalline material efficient impurity band conduction due to strongly interacting acceptors can be achieved in the range of supersaturation. For lower doping levels impurity band conduction is more effective in nanocrystalline SiC. [ABSTRACT FROM AUTHOR]

In this paper the authors investigate the effect of implantation temperature on the structural properties of diamond implanted with high fluences of Si between 5.3×1017 Si cm-2 and 1×1018 Si cm-2. In order to reduce radiation-induced damage and to enhance SiC formation the implantations were performed at elevated temperatures in the range from 900 to 1200 °C. Subsequently, all samples were annealed for 10 min at 1500 °C in a rf-heated furnace. X-ray diffraction revealed the formation of cubic SiC nanocrystallites in a buried layer inside the implanted diamond. The implantation-induced damage was assessed by analyzing graphitization of the surface-near layer using Raman spectroscopy. With increasing Si fluence the implantation-induced damage rises and the nearly perfect alignment of the formed SiC crystallites within the host diamond lattice deteriorates. However, raising the implantation temperature from 900 to 1000 °C reduces the damage in the diamond and increases the amount, size, and epitaxial alignment of the crystalline SiC precipitates. Further increase of the implantation temperature gives no improvement in the quality of the SiC-rich layer. Instead, the damaged diamond converts into graphite and the formation of SiC crystallites is obstructed. [ABSTRACT FROM AUTHOR]

Epitaxial SiC nanocrystals are fabricated by high-fluence Si implantation into natural diamond at elevated temperatures between 760 and 1100 °C. Fluences under investigation range from 4.5 to 6.2×1017 Si cm-2. This implantation scheme yields a buried layer rich of epitaxially aligned SiC nanocrystals within slightly damaged diamond. The generation of a small fraction of graphitic sp2 bonds of up to 15% in the diamond host matrix cannot be avoided. Unintentional coimplantation with nitrogen results in a very high doping level of more than 1021 cm-3. Resistivity and Hall measurements in van der Pauw geometry reveal a high, thermally stable n-type conductivity with electron concentrations exceeding 1020 cm-3 and mobilities higher than 2 cm2 /V s. It is supposed that both the SiC regions as well as the diamond matrix exhibit n-type conductivity and that the electron transport occurs across the low-resistivity SiC nanograins. In the SiC nanocrystals the electrons originate from nitrogen donors whereas in diamond defects are responsible for the electron conductivity. The formation of disordered graphite, which leads to low electron mobility, is substantially reduced by the SiC formation. [ABSTRACT FROM AUTHOR]

Al supersaturated SiC layers (5×1020 Al cm-3) were produced by multienergy, high-dose ion implantation into 6H- and 4H-SiC. Several implantation schemes with varying implantation sequence and temperature were investigated. In dependence on the implantation conditions damaged single-crystalline, amorphous, or nanocrystalline layers were formed. The layer morphology and Al distribution in the as-implanted state as well as structural changes and related Al redistribution after high-temperature annealing (1500–1700 °C) were characterized by cross-sectional transmission electron microscopy, Rutherford backscattering spectrometry in combination with ion channeling, atomic force microscopy, and secondary-ion mass spectrometry. Remarkable Al redistribution effects have been found after annealing of Al supersaturated SiC. During high-temperature annealing Al atoms in excess to the solid solubility (2×1020 Al cm-3) tend to precipitate in single-crystalline SiC whereas they diffuse out in amorphous or nanocrystalline SiC. Redistribution of Al with concentration below the solid solubility is governed by transient enhanced diffusion which can be controlled by the annealing scheme. Amorphization of SiC is advantageous in the case of Al doping to levels higher than the solid solubility because it prevents Al precipitation during annealing and helps to form boxlike Al profiles with smooth plateau and abrupt edge. [ABSTRACT FROM AUTHOR]

The sheet resistance and structural properties of high-fluence Si-implanted diamond were investigated. In order to minimize the radiation damage and to facilitate SiC formation the implantation was performed at 900°C. All samples were subsequently annealed in a rf-heated furnace at 1500°C for 10 min in order to remove defects and thermally unstable phases. X-ray diffraction, infrared absorption spectrometry, and high-resolution cross-sectional transmission electron microscopy revealed the formation of a buried layer inside the implanted diamond, which contains SiC nanocrystallites. These SiC nanocrystals have a cubic structure and are nearly perfectly aligned with the diamond lattice. Raman spectroscopy was applied to analyze radiation-damage-induced graphitization in dependence on the implantation conditions. The sheet resistance of the samples was measured as function of temperature by four point probe technique in van-der-Pauw geometry. The decrease of the sheet resistance with increasing ion fluence unambiguously shows the influence of implantation-induced damage. The behavior of the sheet resistance can strongly be modified by additional nitrogen implantation. The resulting higher conductivity is interpreted as partial incorporation of the nitrogen donor into the SiC nanocrystals. However, when the Si fluence exceeds a critical value of 5.3×10[SUP17]Si[SUP+]cm[SUP-2] at 900°C the diamond is irreversibly damaged and defect related conductivity dominates. [ABSTRACT FROM AUTHOR]

Presents information on a study which discussed the phase formation due to high dose of aluminum implantation into silicon carbide. Microstructure; Chemical reactions and compositional changes; Conclusions.

Studies the effects of high dose ion irradiation through amorphous surface layers on single crystalline of silicon carbide at elevated temperatures. How to interpret the interface shift under ion irradiation; Experimental details; Results and discussion; Conclusions.

Focuses on the use of the step height measurements, x-ray diffraction, and optical microscopy in an attempt to investigate the annealing behavior of amorphous silicon carbon (SiC) layers which were produced by the MeV Si implantation into 6H-SiC. Discovery of two annealing stages; Information on partial crystallization and changes of the amorphous network structure; Analysis of the crystallization kinetics.

Cites an experimental investigation into the ion fluence and temperature dependence of the amorphization of silicon carbide (SiC) using laser reflectometry and Rutherford backscattering spectometry. Information on SiC; Details on the amorphization models used in the investigation; In-depth look at the experiment; Results of the experiment.

Examines the modeling and experimental results of ion-beam-induced interfacial amorphization in silicon. Dependence on substrate temperature, ion flux and nuclear energy deposition at the amorphous/crystalline interface; Basis of the model on ballistic transport effects; Generation of a thermal ion-beam-induced defect; Thermally activated recombination of defects.

Focuses on a study which examined amorphization of 6H-SiC with germanium ions at room temperature and subsequent ion-beam-induced epitaxial crystallization (IBIEC) with silicon ions. Significance of SiC to the semiconductor industry; Experimental results; Results and discussion.

Presents information on a study that performed the analysis of silicon carbide films obtained by carbon ion implantation into amorphous by infrared and Raman scattering spectroscopies, transmission electron microscopy. Experimental procedure; Results and discussion on the study.

We report on large negative and positive magnetoresistance in inhomogeneous, insulating Si:Ga films belowa critical temperature of about 7 K. The magnetoresistance effect exceeds 300%at temperatures below3Kand fields of 8T. The comparison of the transport properties of superconducting samples with that of insulating ones reveals that the large magnetoresistance is associated with the appearance of local superconductivity. A simple phenomenological model based on localized Cooper pairs and hopping quasiparticles is able to describe the temperature and magnetic field dependence of the sheet resistance of such films. [ABSTRACT FROM AUTHOR]

Silicon films with Ga-rich nanoprecipitates are superconductors or insulators in dependence on their normal state resistance. Even in the insulating state of the film superconducting nanoprecipitates exist below the critical temperature of 7 K and determine its complex transport behavior. In this range sometimes large, random resistance jumps appear that are accompanied by little temperature changes. The resistance fluctuates between a well-defined low-resistance value and a broader band of higher resistances. Jumps to higher resistance are associated with a temperature decrease and vice versa. We present experimental results on these fluctuations and suppose a first order phase transition in the film as probable origin. [ABSTRACT FROM AUTHOR]

We report new experimental results on how superconductivity in gallium-doped germanium (Ge:Ga) is influenced by hole concentration and microstructure. Ion implantation and subsequent flash-lamp annealing at various temperatures have been utilized to prepare highly p-doped thin films consisting of nanocrystalline and epitaxially grown sublayers with Ga-peak concentrations of up to 8 at. %. Successive structural investigations were carried out by means of Rutherford-backscattering spectrometry in combination with ion channeling, secondary-ion-mass spectrometry, and high-resolution cross-sectional transmission electron microscopy. Hole densities of 1.8·1020 to 5.3·1020 cm-3 (0.4 to 1.2 at. %) were estimated via Hall-effect measurements revealing that only a fraction of the incorporated gallium has been activated electrically to generate free charge carriers. The coincidence of a sufficiently high hole and Ga concentration is required for the formation of a superconducting condensate. Our data reflect a critical hole concentration of around 0.4 at. %. Higher concentrations lead to an increase of Tc from 0.24 to 0.43 K as characterized by electrical-transport measurements. A short mean-free path indicates superconductivity in the dirty limit. In addition, small critical-current densities of max. 20 kA/m2 point to a large impact of the microstructure. [ABSTRACT FROM AUTHOR]

Phosphorus implantation (30 keV, 3×1015 cm-2) into preamorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. During annealing a significant P diffusion in amorphous Ge is not observed. However, the fast solid phase epitaxial regrowth causes a rapid redistribution of P. After completion of the regrowth and at temperatures above 500 °C, a concentration-dependent diffusion of P in crystalline Ge takes place and leads to considerable loss of P toward the surface. An appreciable influence of implantation defects on the diffusion coefficient of P is not detected. For 60 s rapid thermal annealing at 600 °C and for 20 ms flash lamp annealing at 900 °C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ω, respectively, and the maximum electrical activation of P is about 3–7×1019 cm-3. [ABSTRACT FROM AUTHOR]

Presents a study which demonstrates that M.G. Grimaldi's analysis of Rutherford backscattering/channel data on damage production in SiC, cannot be used to calculate the atomic displacement energy. Grimaldi's theories on the damaging process and amorphization of SiC by ion implantation.

Comments on an article about the evidence of enhanced epitaxial crystallization at low temperature by inelastic electronic scattering of mega-electron-volt heavy-ion-beam irradiation. Interpretation to the results on epitaxial crystallization of silicon by mega-electron-volt heavy-ion-beam irradiation; Recommendations.

We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology. [ABSTRACT FROM AUTHOR]

Shallow n+ layers in Ge are formed by phosphorus implantation and subsequent millisecond flash lamp annealing. Present investigations are focused on the dependence of P redistribution, diffusion and electrical activation on heat input into the sample and flash duration. In contrast to conventional annealing procedures an activation up to 6.5×1019 cm-3 is achieved without any dopant redistribution and noticeable diffusion. Present results suggest that independently of pretreatment the maximum activation should be obtained at a flash energy that corresponds to the onset of P diffusion. The deactivation of P is explained qualitatively by mass action analysis which takes into account the formation of phosphorus-vacancy clusters. [ABSTRACT FROM AUTHOR]

High-dose carbon implantation (3 × 10[sup 17] and 1 × 10[sup 18] ions/cm²) into cubic SiC on Si was carried out at elevated temperatures (600 to 1200°C) and different dose rates (1×10[sup 13] to 1.5 × 10[sup 14] cm[sup -2] s[sup -1]). Transmission electron microscopy revealed the formation of either graphite or diamond precipitates, depending on the implantation parameters. In all cases, the diamond grains were epitaxial to the SiC lattice, while the graphite was textured. The minimum temperature for diamond formation was 900 °C, while graphite formed at 600 °C. The synthesized phase depends as well on the dose rate; graphite was formed at 900 °C with a high dose rate. Obviously, a critical temperature for diamond formation exists and increases with increasing dose rate. This behavior is explained by the competition between the accumulation and dynamic annealing of radiation defects in the SiC lattice, which acts as a template for diamond nucleation. Diamond grains with diameters as large as 10 nm have been observed after implantation at 1200 °C. [ABSTRACT FROM AUTHOR]

Low-resistivity (<0.1 Ωcm), p-type SiC layers of about 500 nm width and targeted acceptor concentrations of 1.5×10[sup 20] cm[sup -3] and 5.0×10[sup 20] cm[sup -3] were produced by the combination of high-dose (1.0 and 3.3×10[sup 16] cm[sup -2]), multienergy (50-450 keV) Al[sup +] ion implantation of 6H-SiC at -130°C, ion-beam-induced crystallization with 500 keV, 5×10[sup 15] Si[sup +] cm[sup -2] at 500°C and subsequent furnace annealing at 1500°C for 10 min. The implanted SiC layers have a nanocrystalline structure consisting of randomly oriented grains of mainly 3C-SiC. The electrical properties of the doped, nanocrystalline layers were investigated by sheet resistance and Hall measurements in dependence on temperature and compared with results from single-crystalline reference samples. In comparison with the standard doping process, the hole concentration at 50 °C is enhanced by more than one order of magnitude from 9.0×10[sup 17] cm[sup -3] to 1.6×10[sup 19] cm[sup -3] in the case of 1.5×10[sup 20] Al cm[sup -3] and from 6.1×10[sup 18] cm[sup -3] to 8.0×10[sup 19] cm[sup -3] in the case of 5.0 ×10[sup 20] Al cm[sup -3], respectively. It can be speculated that the loss of active Al acceptors by precipitation is reduced in the nanocrystalline layers and, therefore, the critical concentration for the formation of an impurity band can be achieved. [ABSTRACT FROM AUTHOR]

Examines the aluminum carbide formation in silicon carbide (SiC) with high dose of aluminum ion implantation. Properties of SiC for electronic and mechanical applications; Similarities in the aluminum carbide precipitates with the silicon carbide matrix.

Measures the density of amorphous silicon carbide layers by x-ray reflectometry. Comparison to the results of step height measurements; Investigation of density as function of depth using reactive ion etching; Homogeneity of the density reduction across the whole layer thickness.

Examines the temperature dependence of ion beam induced interfacial amorphization process of silicon semiconductors. Techniques used in the analysis; Discussion of observed three regimes due to temperature variations; Basis for the explanation of the low-temperature regime.

Investigates the ion-beam-induced recrystallization of amorphous surface layers on single-crystalline silicon carbide substrates. Use of transmission electron microscopy, Rutherford backsetting spectroscopy and channeling; Efficiency of irradiation to reduce the temperature of epitaxial layer regrowth; Nucleation of recrystalline materials.

Heavily Ga implanted Si nanolayers covered with a thin SiO2 layer exhibit a superconductor-insulator transition in dependence on annealing conditions. The transition characteristics resemble those of ultrathin quench-condensed metal films although the implanted layer differs clearly in composition, width, and nanostructure. This implies a general physical mechanism for the superconductor-insulator transition in thin, disordered layers which is supposed to be a quantum phase transition between dual states-the superconducting and the superinsulating one. There is a resistance criterion for the phase transition closely associated with a critical hole concentration. [ABSTRACT FROM AUTHOR]

Natural IIa diamond was implanted at 90 keV to 1x10[sup 15] N[sup +]/cm[sup 2] and subsequently at 150 keV to 3x10[sup 17] Si[sup +]/cm[sup 2] at a temperature of 900 °C. The structure of the implanted diamond region was investigated by high-resolution cross-sectional transmission electron microscopy, Raman, and infrared absorption spectrometry. A buried layer with crystalline 3C-SiC domains in perfect epitaxial relation to the diamond substrate was detected. Amorphization and graphitization were completely prevented by the elevated temperature during the implantation. Resistance measurements demonstrated low electrical resistivity in the implanted regions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A high dose of 1x10[sup 18] cm[sup -2], 60 keV carbon ions was implanted into single crystalline 6H silicon carbide (SiC) at elevated temperatures. The formation of carbon phases in the crystalline SiC lattice was investigated by cross sectional transmission electron microscopy. An amorphous, carbon rich phase was produced at 300 °C. Precipitates of graphite were obtained at 600 °C, whereas at 900 °C small diamond grains were produced. These grains are in perfect epitaxial relation with the surrounding SiC lattice. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]