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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]

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]

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.

Cubic SiC is implanted with carbon ions at 600, 900, 1100 and 1200 °C. X-ray diffraction and transmission electron microscopy revealed the influence of implantation temperature and dose rate on the formation of graphite and diamond precipitates, respectively. The high dose carbon implantation at 600 °C yields graphite already in a textured form. Spherical diamond grains, which are always epitaxial to the SiC, are found in samples implanted at 900 °C or higher. Increasing the dose rate leads to formation of graphite instead of diamond at 900 °C as well. Hence, a critical temperature for diamond evolution exists, which depends on dose rate. Size and shape of the formed diamond precipitates is not influenced by dose rate within the investigated range. Increasing the fluence results in bigger diamond nanocrystals, which are bordered by facets. [Copyright &y& Elsevier]

Nanocrystals of silicon carbide were synthesized inside natural diamond using high dose silicon implantation. In order to retain the diamond structure implantation was done at 900 °C. The samples were subsequently annealed in an rf-heated furnace at 1500 °C for 10 min. X-Ray diffraction (XRD), IR absorption spectrometry and high-resolution cross-sectional transmission electron microscopy (HRTEM) are used to investigate formation and structure of SiC nanocrystallites in the implanted diamond. Raman spectroscopy contributed to trace implantation-induced destruction of the diamond. A first characterization of the electrical properties of the implanted and annealed samples is done by four-point probe measurements. The results indicate a highly conductive, buried layer inside the diamond. This layer contains cubic SiC nanocrystals, which are perfectly aligned with the diamond lattice. However, when fluence exceeds a critical value of 5.3×1017 Si+ cm−2, the diamond is irreversibly damaged and defect conduction type dominates. [Copyright &y& Elsevier]

Ion-beam-induced crystallization was used to transform amorphized, heavily Al doped SiC layers to nanocrystalline material. The morphology of the as-implanted and the annealed layers was studied by XTEM. The electrical properties were analyzed by sheet resistance and Hall measurements and compared with crystalline reference samples. A high-temperature annealing step is necessary to activate the implanted Al acceptor atoms. During annealing the mean grain size of the nanocrystals grow from 3 to 35 nm. The Al doped, nanocrystalline SiC has a much lower sheet resistance than the crystalline reference samples. It was found that this is due to the enhanced hole concentration which could be explained by a higher solid solubility of Al in the nanocrystalline SiC. [Copyright &y& Elsevier]

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.

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 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.

Abstract: The combination of microbeam implantation and in-situ micro RBS/channeling analysis in the Rossendorf nuclear microprobe facility enables crystal damage studies with high current densities not achievable in standard ion implantation experiments. Si(100) samples were implanted with 600keV Si+ ions and a fluence of 1×1016 cm−2. Using a beam spot of 200μm×200μm current densities from 4 to 120μA/cm2 were obtained. The substrate temperature was varied between RT and 265°C. The implanted regions were subsequently analysed by micro RBS/channeling with a 3MeV He+ beam having a spot size of 50μm×50μm. Crystal damage up to amorphisation was observed in dependence on the substrate temperature. Above a critical temperature T C no amorphisation occurs. T C was determined for each series of samples implanted with the same ion current density j. It was found that the empirical Arrhenius relation j ∼exp(−E a/kT C), known from standard implantation experiments, is also valid at high current densities. The observed Arrhenius law can be derived from a model of epitaxial crystallisation stimulated by defect diffusion. [Copyright &y& Elsevier]

Nanometer-sized SiC precipitates were synthesized at 450 °C in Si by simultaneous dual beam implantation of C+ and Si+ ions and subsequent annealing. The results are compared with those of sequential dual beam implantation and of single beam implantation. Two types of SiC precipitates were found. Precipitates of type I with a diameter of d=4–5 nm consist of 3C-SiC epitaxially oriented with the Si matrix. They were formed already in the as-implanted state and do not grow further during subsequent annealing. The SiC precipitates of type II with d&ap;10 nm are not oriented with the Si matrix and grow exclusively during the subsequent annealing. The high growth velocity, the misorientation in regard to the Si matrix and the lower concentration of type II precipitates can be explained by the assumption that these precipitates were formed in an amorphous substrate which modifies their interface energy. [Copyright &y& Elsevier]