100 research outputs found
Electronic properties and dopant pairing behavior of manganese in boron-doped silicon
Boron-doped silicon wafers implanted with low doses of manganese have been analyzed by means of deep-level transient spectroscopy(DLTS), injection-dependent lifetime spectroscopy, and temperature-dependent lifetime spectroscopy. While DLTSmeasurements allow the defect levels and majority carrier capture cross sections to be determined, the lifetime spectroscopy techniques allow analysis of the dominant recombination levels and the corresponding ratios of the capture cross sections. Interstitialmanganese and manganese-boron pairs were found to coexist, and their defect parameters have been investigated.One of the authors T.R. gratefully acknowledges a
scholarship of the German Federal Environmental Foundation
Deutsche Bundesstiftung Umwelt. Another D.M. is
supported by an Australian Research Council QEII Fellowship
Specific heat and electronic states of superconducting boron-doped silicon carbide
The discoveries of superconductivity in the heavily-boron doped
semiconductors diamond (C:B) in 2004 and silicon (Si:B) in 2006 have renewed
the interest in the physics of the superconducting state of doped
semiconductors. Recently, we discovered superconductivity in the closely
related ''mixed'' system heavily boron-doped silcon carbide (SiC:B).
Interestingly, the latter compound is a type-I superconductor whereas the two
aforementioned materials are type-II. In this paper we present an extensive
analysis of our recent specific-heat study, as well as the band structure and
expected Fermi surfaces. We observe an apparent quadratic temperature
dependence of the electronic specific heat in the superconducting state.
Possible reasons are a nodal gap structure or a residual density of states due
to non-superconducting parts of the sample. The basic superconducting
parameters are estimated in a Ginzburg-Landau framework. We compare and discuss
our results with those reported for C:B and Si:B. Finally, we comment on
possible origins of the difference in the superconductivity of SiC:B compared
to the two ''parent'' materials C:B and Si:B.Comment: 9 pages, 7 figures, 2 tables, submitted to Phys. Rev.
Anharmonic vibrations of the dicarbon antisite defect in 4H-SiC
Dicarbon antisite defects were created by either electron irradiation or ion implantation into 4H-SiC. The no-phonon lines from the dicarbon antisite defect center were observed with their phonon replicas. The stretch frequencies of the defect were observed up to the fifth harmonic. The Morse potential model accounts for the anharmonicity quite well and gives a very good prediction of the vibration energies up to the fifth harmonic with an error of less than 1%. First principles calculations show that the model of a dicarbon antisite defect along with its four nearest neighboring carbon atoms can explain the observed anharmonicity
Electrical activation of high concentrations of N+ and P+ ions implanted into 4H-SiC
Comparative Hall effect investigations are conducted on N- and P-implanted as well as on (N+P)-coimplanted 4H-SiC epilayers. Box profiles with three different mean concentrations ranging from 2.5x10 (exp 18) to 3x10 (exp 20) cm-3 to a depth of 0.8 µm are implanted at 500 °C into the (0001)-face of the initially p-type (Al-doped) epilayers. Postimplantation anneals at 1700 °C for 30 min are conducted to electrically activate the implanted N+ and P+ ions. Our systematic Hall effect investigations demonstrate that there is a critical donor concentration of (2-5) X 10 (exp 19) cm-3. Below this value, N- and P-donors result in comparable sheet resistances. The critical concentration represents an upper limit for electrically active N donors, while P donors can be activated at concentrations above 10 (exp 20) cm-3. This high concentration of electrically active P donors is responsible for the observed low sheet resistance of 35 Omega, which is about one order of magnitude lower than the minimum sheet resistance achieved by N implantation
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