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ABSTRACT: In narrow channels the properties of the sidewalls can have a crucial effect on both the physics and any device functionality of the electronic transport through these structures. We assess the use of electron beam and "dry etching" fabrication techniques to define sidewalls by studying the influence of the sidewalls on the quantum transmission through the channels and, in particular, show the sidewall scattering to be inelastic in nature and to have implications ranging from electron heating to electron coherence effects.
Canadian Journal of Physics 02/2011; 70:979-984. · 0.86 Impact Factor
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ABSTRACT: We have studied the magnetoresistance of a two-dimensional electron gas (2DEG) subjected to a periodic potential created using electrostatic gates. Periods vary between 100 nm and 500 nm. The detailed behaviour of the magnetoresistance, which includes a positive contribution at very low magnetic fields and oscillatory behaviour periodic in 1/B at higher fields, is explained successfully within a semi-classical framework. The dependence of the magnetoresistance on amplitude of potential and temperature is explained quantitatively. The limits to the validity of the semi-classical approach are derived. By rotating the sample we are able to alter the magnetoresistance in an anisotropic fashion depending on the relative direction between the equipotentials and the axis of rotation. This is interpreted in terms of the in-plane magnetic field allowing the zero-point motion in the confinement direction to be observed in the plane of the 2DEG.
Physica Scripta 01/2007; 1991(T39):169. · 1.20 Impact Factor
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ABSTRACT: We present magnetotransport results for a 2D electron gas (2DEG) subject to the quasi-random magnetic field produced by randomly positioned sub-micron Co dots deposited onto the surface of a GaAs/AlGaAs heterostructure. We observe strong local and non-local anisotropic magnetoresistance for external magnetic fields in the plane of the 2DEG. Monte-Carlo calculations confirm that this is due to the changing topology of the quasi-random magnetic field in which electrons are guided predominantly along contours of zero magnetic field. Comment: 4 pages, 6 figures, submitted to Phys. Rev. B
08/2003;
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ABSTRACT: The resistivity, temperature, and magnetic field dependence of the anomalous Hall effect in a series of metallic Ga <sub>1-x</sub> Mn <sub>x</sub> As thin films with x=0.015 to 0.08 is presented. A quadratic dependence of the anomalous Hall resistance on the resistivity is observed, with a magnitude which is in agreement with Berry phase theories of the anomalous Hall effect in dilute magnetic semiconductors. © 2003 American Institute of Physics.
Journal of Applied Physics 06/2003; · 2.17 Impact Factor
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ABSTRACT: The magnetoresistance in a series of Ga1-xMnxAs samples with 0.2 =< x =< 0.8 have been measured for three mutually orthogonal orientations of the external magnetic field. The anisotropy magnetoresistance decreases with increasing of the Mn content, which means that the magnetic disorder or defects scattering increases with increasing of Mn content. And also the magneto-crystalline anisotropy increases with increasing of Mn concentration.
12/2002;
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ABSTRACT: By studying the Hall effect in a series of low resistivity Ga1−xMnxAs samples, accurate values for the hole density p, Mn concentration x, and Curie temperature TC are obtained over the range 0.015 ⩽ x ⩽ 0.08. The hole density corresponds to 90% of the Mn concentration at low x, and has a maximum value of 1.0×1027 m−3 when TC = 125 K. These data allow the first meaningful comparison of mean field predicted Curie temperatures with experiment over a wide range of x. The theory is in qualitative agreement with experiment, but overestimates TC at large x and underestimates TC at low x. © 2002 American Institute of Physics.
Applied Physics Letters 10/2002; 81(16):3010-3012. · 3.84 Impact Factor
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ABSTRACT: The resistivity, temperature, and magnetic field dependence of the anomalous Hall effect in a series of metallic Ga1-xMnxAs thin films with 0.015=<x=<0.08 is presented. A quadratic dependence of the anomalous Hall resistance on the resistivity is observed, with a magnitude which is in agreement with Berry phase theories of the anomalous Hall effect in dilute magnetic semiconductors. Comment: 3 pages, 4 figures, MMM conference proceedings
09/2002;
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ABSTRACT: We have investigated the substrate orientation-dependence of InAs/GaAs quantum dot growth by photoluminescence spectroscopy in very high magnetic fields. An abrupt change from one-dimensional to three-dimensional charge confinement is observed for InAs deposited on (100) GaAs. On the tilted (311)B substrates, the quantum dot morphology is different, resulting in a weaker charge confinement that gradually increases with the amount of deposited InAs. At 1.9 monolayers, the quantum-dot confinement on this substrate orientation is as effective as for the (100) oriented substrates. By studying the confinement of the charges in samples with quantum dots at different stages of development, we are able to give insight into the quantum-dot formation process. © 2002 American Institute of Physics.
Applied Physics Letters 08/2002; 81(8):1480-1482. · 3.84 Impact Factor
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A. Patanè,
A. Ignatov,
L. Eaves, P. C. Main,
M. Henini,
E. Schomburg,
R. Scheuerer,
K. F. Renk,
V. M. Ustinov,
A. E. Zhukov,
A. R. Kovsh
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ABSTRACT: We investigate the electronic properties of wide miniband (~100 meV)
GaAs/AlAs superlattice structures in which the tunnel barriers are
formed from planar arrays of AlAs islands. By studying the effect of an
in-plane magnetic field on the miniband conduction, we determine the
strength and anisotropy of the rate of electron scattering by the island
arrays.
Physical review. B, Condensed matter 07/2002; 66(7):75325.
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ABSTRACT: By studying the Hall effect in a series of low resistivity Ga1-xMnxAs samples, accurate values for the hole density p, Mn concentration x, and Curie temperature Tc are obtained over the range 0.015=<x=<0.08. The hole density corresponds to 90% of the Mn concentration at low x, and has a maximum value of 1.0x10-27 m-3 when Tc=125K for x=0.06. This data allows the first meaningful comparison of mean field predicted Curie temperatures with experiment over a wide range of x. The theory is in qualitative agreement with experiment, but overestimates Tc at large x and underestimates TC at low x.
06/2002;
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ABSTRACT: We study electron miniband magneto-transport in GaAs/AlAs superlattices with AlAs barriers of two monolayers. Here, the two-dimensional AlAs barrier comprises an in-plane distribution of AlAs islands. We use magneto-transport to probe both the rate and the anisotropy of the electron scattering associated with the islands.
Physica E Low-dimensional Systems and Nanostructures 01/2002; 13(2):786-789. · 1.53 Impact Factor
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ABSTRACT: We use an array of gate electrodes to control the electrostatic profile in a layer of self-assembled InAs quantum dots. In combination with magnetotunneling spectroscopy, this allows us to identify and measure the energy levels and wave functions associated with the ground and excited state of an individual quantum dot. © 2001 American Institute of Physics.
Applied Physics Letters 12/2001; · 3.84 Impact Factor
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ABSTRACT: We study p-i-n diodes incorporating InAs/AlAs self-assembled quantum dots (QDs) to probe the electron and hole levels of the dots. A comparative analysis of capacitance-voltage, current-voltage and electroluminescence measurements shows that p-i-n structures could be successfully used as QD spectrometers.
Nanotechnology 11/2001; 12(4):515. · 3.98 Impact Factor
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ABSTRACT: We present experimental results for hybrid
ferromagnet/semiconductor devices in which 2D electrons propagate
through sub-micron width magnetic barriers. Magnetoresistances, MR, of
~1000% are found at low temperatures and ~1% at room temperature. We
compared the measured behavior with numerical calculations and give the
conditions needed to achieve large room temperature MR
IEEE Transactions on Magnetics 08/2001; · 1.36 Impact Factor
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ABSTRACT: We use magnetotunnelling spectroscopy as a non-invasive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The images reveal clearly the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states.
07/2001;
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ABSTRACT: We present an experimental study of electron wave functions in InAs/GaAs self-assembled quantum dots by magnetotunneling spectroscopy.
The electronic wave functions have a biaxial symmetry in the growth plane, with axes corresponding to the main crystallographic
directions in the growth plane. Moreover, we observed the in-plane anisotropy of the subbands of the quantum well.
JETP Letters 06/2001; 74(1):41-45. · 1.35 Impact Factor
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ABSTRACT: We have measured the magnetic domain patterns in Co/Pd multilayers of varying thickness using magnetic force microscopy in the presence of an external magnetic field applied perpendicular to the multilayers. We find that the domain patterns evolution is in qualitative agreement with existing theories for single layer thin films. Our results are in reasonable agreement with a theoretical model of domains appropriate to multilayer films. © 2001 American Institute of Physics.
Journal of Applied Physics 05/2001; 89(11):7534-7536. · 2.17 Impact Factor
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ABSTRACT: We investigate indium interdiffusion in InAs/(AlGa)As self-assembled quantum dots by studying the changes in the optical properties of the system induced by ion implantation and/or thermal annealing. Interdiffusion of In–Ga and In–Al atoms at the interface between the dot and the (AlGa)As barrier takes place in as-grown samples and is enhanced by the postgrowth treatments. In contrast to the proposed interdiffusion as the way for suppressing the optical emission from the wetting layer, we show that it drives the system towards a predominantly two-dimensional morphology. © 2001 American Institute of Physics.
Journal of Applied Physics 05/2001; 89(11):6044-6047. · 2.17 Impact Factor
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Physica Status Solidi B-basic Solid State Physics - PHYS STATUS SOLIDI B-BASIC SO. 01/2001; 224(1):41-45.
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ABSTRACT: Low-temperature frequency-dependent conductivity measurements on lightly doped n-type layers of GaAs have been made to investigate the large discrepancy between existing data and recent theory by Summerfield and Butcher (1982). The authors' new measurements are in qualitative agreement with the theory.
Journal of Physics C Solid State Physics 11/2000; 17(13):L345.
