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11 Dec 2000

Volume 77, Issue 24, pp. 3881-4064

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High sensitivity measurement of implanted As in the presence of Ge in GexSi1−x/Si layered alloys using trace element accelerator mass spectrometry

S. A. Datar, Liying Wu, B. N. Guo, M. Nigam, D. Necsoiu, Y. J. Zhai, D. E. Smith, C. Yang, M. E. Bouanani, J. J. Lee, and F. D. McDaniel

Appl. Phys. Lett. 77, 3974 (2000); http://dx.doi.org/10.1063/1.1331093 (3 pages) | Cited 3 times

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Various devices can be realized on strained GeSi/Si substrates by doping the substrate with different impurities such as As. As is an n-type dopant in both Ge and Si. As cross contamination can also arise during germanium preamorphization implantation due to inadequate mass resolution in the implanter. Thus, it is important to be able to accurately measure low-level As concentrations in the presence of Ge. Secondary ion mass spectrometry (SIMS) is the standard technique for these types of measurements but is constrained by mass interferences from molecular ions (74GeH, 29Si30Si16O). The trace element accelerator mass accelerator technique allows the breakup of interfering molecules. As is measured in a GeSi matrix with sensitivity significantly better than SIMS. © 2000 American Institute of Physics.
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61.72.S- Impurities in crystals
61.72.up Other materials
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Alkaline metal-doped n-type semiconducting nanotubes as quantum dots

Jing Kong, Chongwu Zhou, Erhan Yenilmez, and Hongjie Dai

Appl. Phys. Lett. 77, 3977 (2000); http://dx.doi.org/10.1063/1.1331088 (3 pages) | Cited 63 times

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A 0.4 μm long semiconducting single-walled carbon nanotube is doped into n type by potassium (K) vapor. Electrical measurements of the doped nanotube reveal single-electron charging at temperatures up to 160 K. The K-doped sample manifests as a single quantum dot or multiple quantum dots in series depending on the range of applied gate voltage. This is explained by an inhomogeneous doping profile along the nanotube length. Similarities between K-doped nanotubes and silicon-based quantum dots and the possibility of room-temperature nanotube single-electron transistors are discussed. © 2000 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
81.05.ub Fullerenes and related materials
73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Gv Single electron devices
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Infrared conductivity mapping for nanoelectronics

B. Knoll and F. Keilmann

Appl. Phys. Lett. 77, 3980 (2000); http://dx.doi.org/10.1063/1.1330756 (3 pages) | Cited 44 times

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With ever shrinking dimensions in microelectronics, the conductivity performance of charge carriers approaches physical limits and demands tighter control. We show that near-field microscopy carried out at sufficiently long infrared wavelengths—below the plasma frequency—selectively detects and characterizes subsurface mobile carriers with 30 nm resolution, timely for next generation chips as well as for fundamental research, e.g., on low-dimensional electron systems. © 2000 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects

High-resolution observation of the growth motion of elements on surfaces and at interfaces

Toshiro Yamanaka, Naoharu Shimomura, and Shozo Ino

Appl. Phys. Lett. 77, 3983 (2000); http://dx.doi.org/10.1063/1.1332979 (3 pages) | Cited 3 times

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The results of high-resolution, real-space observations of the behaviors of elements on surfaces and at interfaces during growth of Ga on Si(111)-√×√-Ag are presented. Site exchange and surrounding other elements were directly observed using a high-resolution ultrahigh vacuum scanning electron microscope (SEM) newly combined with characteristic x-ray spectroscopy under a grazing detection-angle condition. Compared with the resolution of conventional SEM-energy dispersive x-ray spectrometry (several μm), resolution in elementary analysis has been significantly improved due to a small beam size and cut off of x-rays from deep regions, and local elementary analysis of surface structures of only about 10–20 nm in size is possible by the present method. © 2000 American Institute of Physics.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Investigation of surface treatments for nonalloyed ohmic contact formation in Ti/Al contacts to n-type GaN

Yow-Jon Lin and Ching-Ting Lee

Appl. Phys. Lett. 77, 3986 (2000); http://dx.doi.org/10.1063/1.1332827 (3 pages) | Cited 40 times

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To investigate the possibility of preparing a nonalloyed ohmic contact to n-type GaN, the effects of GaN surface treatments on the metal/GaN interface were studied using x-ray photoelectron spectroscopy. A specific contact resistance of 5.0×10−5 Ω cm2 for the Ti/Al nonalloyed ohmic contacts to (NH4)2Sx-treated n-type GaN can be obtained. The nonalloyed ohmic contact formation would be impeded by the native oxide and the hydroxyl induced from the surface treatment of chemical solutions. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
81.65.-b Surface treatments
79.60.Jv Interfaces; heterostructures; nanostructures

Electrical spin injection across air-exposed epitaxially regrown semiconductor interfaces

Y. D. Park, B. T. Jonker, B. R. Bennett, G. Itskos, M. Furis, G. Kioseoglou, and A. Petrou

Appl. Phys. Lett. 77, 3989 (2000); http://dx.doi.org/10.1063/1.1332826 (3 pages) | Cited 42 times

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We have fabricated spin-polarized light-emitting diode structures via epitaxial regrowth of Zn1−xMnxSe on air-exposed surfaces of AlyGa1−yAs/GaAs quantum wells. No passivation procedures were used to protect or prepare the III–V surface. The electroluminescence is strongly circularly polarized due to the electrical injection of spin-polarized electrons from the ZnMnSe contact into the GaAs quantum well. An analysis of the optical polarization yields a lower bound of 65% for the spin injection efficiency. These results demonstrate the robustness of the spin injection process in the diffusive transport regime, and attest to the practicality of manufacturing semiconductor-based spin injection devices. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Li Other semiconductors

Scanning-tunneling-microscopy-induced optical spectroscopy of a single GaAs quantum well

Ph. Dumas, V. Derycke, I. V. Makarenko, R. Houdré, P. Guaino, A. Downes, and F. Salvan

Appl. Phys. Lett. 77, 3992 (2000); http://dx.doi.org/10.1063/1.1330219 (3 pages) | Cited 5 times

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We have investigated the scanning-tunneling-microscopy-induced light emission originating from a single GaAs quantum well. The 5-nm-thick quantum well was confined between a 30-nm-thick AlAs barrier (grown onto a GaAs substrate) and the vacuum tunneling gap. Low currents ensured a nonintrusive investigation of the surface. Optical spectroscopy of the light emitted while injecting electrons from the tip revealed two peaks associated with the band-to-band recombination in the bulk GaAs (at 1.43 eV), and with the electronic transition in the surface quantum well (at 1.52 eV). The surface sensitivity of the technique is evidenced and the quantum efficiencies of both processes are estimated. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.60.Fi Electroluminescence
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.25.+i Surface conductivity and carrier phenomena

Quantized tunneling current in the metallic nanogaps formed by electrodeposition and etching

C. Z. Li, H. X. He, and N. J. Tao

Appl. Phys. Lett. 77, 3995 (2000); http://dx.doi.org/10.1063/1.1332406 (3 pages) | Cited 57 times

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We have studied electron tunneling across the gap between two electrodes as the gap is varied by electrodeposition and etching. The tunneling current tends to change in a stepwise fashion, corresponding to a discrete change of the gap width. The stepwise change is due to the discrete nature of atoms and a series of structural relaxations of the atoms at the electrodes between stable configurations upon deposition and etching. By stabilizing the tunneling current on various steps using a feedback loop, we have demonstrated that stable molecular-scale gaps can be fabricated with subangstrom precision. © 2000 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
73.40.Gk Tunneling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Pq Electrodeposition, electroplating

Two-dimensional electron-gas AlN/GaN heterostructures with extremely thin AlN barriers

I. P. Smorchkova, S. Keller, S. Heikman, C. R. Elsass, B. Heying, P. Fini, J. S. Speck, and U. K. Mishra

Appl. Phys. Lett. 77, 3998 (2000); http://dx.doi.org/10.1063/1.1332408 (3 pages) | Cited 41 times

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Plasma-assisted molecular-beam epitaxy is used to grow a set of two-dimensional electron-gas AlN/GaN structures with AlN barrier thicknesses varied between 24 and 50 Å. The density of the two-dimensional electron gas formed at the GaN/AlN interface increases from 1.51×1013 cm−2 for the AlN barrier width of 24 Å to 3.65×1013 cm−2 for the AlN barrier width of 49 Å. The increase in the electron sheet density is accompanied by a decrease in electron mobility related to tensile strain relaxation and enhanced interface roughness scattering. It is shown that room-temperature sheet resistances below 200 Ω/□ can be achieved in AlN/GaN high electron mobility transistor structures with 35–45 Å AlN barriers. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states

Atomic-scale study of GaMnAs/GaAs layers

B. Grandidier, J. P. Nys, C. Delerue, D. Stiévenard, Y. Higo, and M. Tanaka

Appl. Phys. Lett. 77, 4001 (2000); http://dx.doi.org/10.1063/1.1322052 (3 pages) | Cited 59 times

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Cross-sectional scanning tunneling microscopy was used to study GaMnAs diluted magnetic semiconductors grown by low temperature molecular beam epitaxy. The Ga1−xMnxAs layer, containing a concentration of x = 0.005, shows that the dominant defect in the material is the arsenic antisite. Mn ions can also be resolved and show a signature distinct from the arsenic antisites. Spectroscopic measurements are perfomed to study the variation of the Fermi level between the Ga0.995Mn0.005As and GaAs layers. The Mn ions act as acceptor dopants. However, for x = 0.005, the Mn concentration in comparison with the As antisite concentration is too small to induce a significant change of the Fermi level from the midgap position, preventing the layer from being ferromagnetic. © 2000 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
71.20.Nr Semiconductor compounds

Doping of 6H–SiC by selective diffusion of boron

S. I. Soloviev, Y. Gao, and T. S. Sudarshan

Appl. Phys. Lett. 77, 4004 (2000); http://dx.doi.org/10.1063/1.1329328 (3 pages) | Cited 10 times

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Experimental evidence of selective boron doping of 6H–SiC via diffusion is given. Selective diffusion has been realized at 1800–2100 °C using graphite film as a protecting mask. Cathodoluminescence measurements as well as an anodic oxidation technique have been employed to identify the local doped regions. In addition, a diffused planar p–n diode based on the local p-type emitter region was fabricated. The ideality factor extracted from current–voltage characteristics was 1.97, which indicates that the Shockley–Hall–Read recombination is the dominant mechanism in the conduction region. The value of breakdown voltage for this diode measured at room temperature was a little greater than 800 V, and a leakage current density of 5.7×10−6 A/cm2 at 800 V was achieved. © 2000 American Institute of Physics.
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61.72.up Other materials
66.30.J- Diffusion of impurities
78.60.Hk Cathodoluminescence, ionoluminescence
85.30.Kk Junction diodes
73.40.Ei Rectification
85.40.Ry Impurity doping, diffusion and ion implantation technology

Electron cloud effect on current injection across a Schottky contact

B. Nabet, A. Cola, F. Quaranta, M. Cesareo, R. Rossi, R. Fucci, and A. Anwar

Appl. Phys. Lett. 77, 4007 (2000); http://dx.doi.org/10.1063/1.1333690 (3 pages) | Cited 6 times

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The electron cloud that is formed in the narrow gap material in a modulation-doped heterostructure affects the Schottky contact made to the wide gap material. It also influences absorption and collection of the optically generated carriers. Photocurrent spectra, current–voltage, and current–temperature measurements show that the increase in electron cloud density decreases dark current flow while increasing photoresponsivity. We propose that the Coulombic interaction between the confined electron cloud and the emitted electrons from metal to the wide gap material increases the barrier height. The electric field in the direction of growth due to modulation doping accounts for the increase in photoelectron collection efficiency. Implementation of this effect increases efficiency of photodetectors while, simultaneously, reducing the noise due to dark current. © 2000 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Pz Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices

Gettering of Co in Si by high-energy B ion-implantation and by p/p+ epitaxial Si

J. L. Benton, T. Boone, D. C. Jacobson, and C. S. Rafferty

Appl. Phys. Lett. 77, 4010 (2000); http://dx.doi.org/10.1063/1.1332828 (3 pages) | Cited 1 time

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Detection and gettering of Co contamination in processed Si is an important issue in integrated circuit fabrication. In this work, Co was intentionally introduced into Si by ion implantation, and its diffusion monitored by secondary ion mass spectroscopy. The surface layer recombination lifetime in p/p+ epitaxial Si is unaffected by the Co at doses of 1×1011 cm−2 or 1×1012 cm−2. In the case of 2.5 MeV, 4×1014 B/cm2 ion implanted bulk Si, two mechanisms for Co redistribution during high temperature furnace, 900 °C, 30 min, processing are evident. First, regions of high boron concentration provide gettering sites for Co contamination. Second, the final distribution of Co in Si reflects ion-implantation induced defect evolution during annealing. Both mechanisms will operate during device processing and will control the effect of the metal on the electrical properties of the Si. © 2000 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
81.65.Tx Gettering
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.25.+i Surface conductivity and carrier phenomena
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Cc Kinetics of defect formation and annealing
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors

Stability of N- and Ga-polarity GaN surfaces during the growth interruption studied by reflection high-energy electron diffraction

X. Q. Shen, T. Ide, S. H. Cho, M. Shimizu, S. Hara, and H. Okumura

Appl. Phys. Lett. 77, 4013 (2000); http://dx.doi.org/10.1063/1.1333685 (3 pages) | Cited 19 times

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GaN films with N- and Ga-polarity were grown on sapphire (0001) substrates using different buffer layers by plasma-assisted molecular-beam epitaxy. The surface stability of each lattice-polarity film during the growth interruption was studied by reflection high-energy electron diffraction (RHEED). It was found that the surface of N-polarity film was unstable against the exposure to the nitrogen plasma flux, while that of Ga-polarity one was stable. This provides a method to clarify the lattice polarity by the in situ RHEED observation directly. A model is proposed to explain the observed phenomenon, where the origin of the phenomenon is mainly attributed to the differences in surface dynamics processes and morphologies between the two kinds of lattice-polarity films. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
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