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29 Jul 2002

Volume 81, Issue 5, pp. 789-944

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Determination of free hole concentration in ferromagnetic Ga1−xMnxAs using electrochemical capacitance–voltage profiling

K. M. Yu, W. Walukiewicz, T. Wojtowicz, W. L. Lim, X. Liu, Y. Sasaki, M. Dobrowolska, and J. K. Furdyna

Appl. Phys. Lett. 81, 844 (2002); http://dx.doi.org/10.1063/1.1496143 (3 pages) | Cited 30 times

Online Publication Date: 22 July 2002

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We demonstrate that electrochemical capacitance–voltage profiling can be used to determine the free hole concentration in heavily p-type doped low-temperature-grown GaAs films. This provides a simple and reliable method for measuring the hole concentration in ferromagnetic Ga1−xMnxAs semiconductor alloys. The method overcomes the complications that arise from the anomalous Hall effect term which affects standard transport studies of carrier concentration in conducting ferromagnetic materials. Specifically, we find that the maximum Curie temperature of about 111 K found for our Ga0.91Mn0.09As samples corresponds to a hole concentration of 1021 cm−3. © 2002 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Ea III-V semiconductors
82.80.Fk Electrochemical methods
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Ultrahigh room-temperature hole Hall and effective mobility in Si0.3Ge0.7/Ge/Si0.3Ge0.7 heterostructures

T. Irisawa, S. Tokumitsu, T. Hattori, K. Nakagawa, S. Koh, and Y. Shiraki

Appl. Phys. Lett. 81, 847 (2002); http://dx.doi.org/10.1063/1.1497725 (3 pages) | Cited 36 times

Online Publication Date: 22 July 2002

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We have obtained ultrahigh room-temperature (RT) hole Hall and effective mobility in Si0.3Ge0.7/Ge/Si0.3Ge0.7 heterostructures with very small parallel conduction. Reducing parallel conduction was achieved by employing Sb doping in Si0.3Ge0.7 buffer layers, which drastically increased RT hole Hall mobility up to 2100 cm2/V s in the strained Ge channel modulation-doped structures and improved device characteristics of the p-type metal–oxide–semiconductor field-effect transistors with the strained Ge channel. The peak effective mobility reached to 2700 cm2/V s at RT, which was much higher than the bulk Ge drift mobility. © 2002 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
85.30.Tv Field effect devices
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
85.30.De Semiconductor-device characterization, design, and modeling

Pure-carbon ring transistor: Role of topology and structure

Gianaurelio Cuniberti, Juyeon Yi, and Markus Porto

Appl. Phys. Lett. 81, 850 (2002); http://dx.doi.org/10.1063/1.1497195 (3 pages) | Cited 20 times

Online Publication Date: 22 July 2002

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We report results on the rectification properties of a carbon nanotube (CNT) ring transistor, contacted by CNT leads, whose novel features have been recently communicated by H. Watanabe, C. Manabe, T. Shigematsu, and M. Shimizu [Appl. Phys. Lett. 78, 2928 (2001)]. This letter contains results which are validated by the experimental observations. Moreover, we report on additional features of the transmission of this ring device which are associated with the possibility of breaking the lead inversion symmetry. The linear conductance displays a chessboardlike behavior alternated with anomalous zero lines which should be directly observable in experiments. We are also able to discriminate the structural properties showing up in our results (quasione-dimensional confinement) from pure topological effects (ring configuration), thus helping to gain physical intuition on the rich ring phenomenology. © 2002 American Institute of Physics.
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85.35.Kt Nanotube devices
85.65.+h Molecular electronic devices
81.07.Nb Molecular nanostructures
73.63.Fg Nanotubes
73.40.Ei Rectification
81.07.De Nanotubes

Stress-induced electron emission from nanocomposite amorphous carbon thin films

C. H. Poa, R. G. Lacerda, D. C. Cox, S. R. P. Silva, and F. C. Marques

Appl. Phys. Lett. 81, 853 (2002); http://dx.doi.org/10.1063/1.1497442 (3 pages) | Cited 11 times

Online Publication Date: 22 July 2002

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Traditionally, the emission of electrons from materials have been explained using either the Fowler–Nordheim emission mechanism where high electric fields are used to extract electrons from surfaces or using conventional thermal emission where high currents are used to “boil” off electrons to vacuum. In this letter, we propose an alternative mechanism for electron emission from highly compressive thin films based on stress-induced “band structure” modification of nano-ordered sp2 regions in the thin films. Experimental results are recorded which show that the localized compressive stress governs electron emission in the amorphous carbon thin films studied here rather than the surface nanostructures/features or the diamond-like sp3 hybridized bond component. This analysis is in agreement with the concept of an internal or nongeometric field enhancement from sp2 nanostructures giving rise to high dielectric inhomogeneity within the carbon thin film. The results presented could be extended to explain the anomalous field emission behavior of carbon nanotubes. © 2002 American Institute of Physics.
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79.90.+b Other topics in electron and ion emission by liquids and solids and impact phenomena (restricted to new topics in section 79)

Spatial dependence of ultrafast carrier recombination centers of phosphorus-implanted and annealed silicon wafers

Andreas Othonos and Constantinos Christofides

Appl. Phys. Lett. 81, 856 (2002); http://dx.doi.org/10.1063/1.1497723 (3 pages) | Cited 2 times

Online Publication Date: 22 July 2002

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In this letter, the spatial dependence of the carrier recombination centers induced in phosphorus-implanted and annealed silicon wafers have been examined. Ultrafast time-resolved reflectivity measurements of a set of phosphorus-implanted annealed silicon wafers (1016 P+/cm2) as a function of position on the wafer have been carried out, and an x–y map of the carrier lifetime for each of the samples has been obtained. Measurements reveal distinct features of the distribution of carrier recombination centers for the nonannealed and annealed samples between 350 °C and 1100 °C in an area of 36×36 μm2 with resolution better than 3 μm. The presence of islands of clusters in ion-implanted and annealed samples is also discussed in this letter. © 2002 American Institute of Physics.
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61.72.S- Impurities in crystals
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Cn Elemental semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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