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7 Oct 2002

Volume 81, Issue 15, pp. 2677-2902

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Control of the confining potential in ballistic constrictions using a persistent charging effect

S. F. Fischer, G. Apetrii, S. Skaberna, U. Kunze, D. Reuter, and A. D. Wieck

Appl. Phys. Lett. 81, 2779 (2002); http://dx.doi.org/10.1063/1.1511278 (3 pages) | Cited 9 times

Online Publication Date: 30 September 2002

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GaAs/AlGaAs quantum point contacts are fabricated by atomic force microscope lithography and wet chemical etching. The lateral confinement potential of a given ballistic constriction is varied by persistent fractional charging of the donors in the supply layer. A forward bias voltage applied to the gate electrode during sample cooling shifts the conductance threshold at T = 4.2 K towards higher gate voltage due to partial neutralization of the donors. Simultaneously, the width of the quantized conductance plateaus at multiples of 2e2/h decreases. Measurements under finite drain voltage reveal a reduction of the lowest subband separation from ΔE1,2 = 17.5±1 to 13±1 meV as the cooling bias voltage is raised from 0 to +0.6 V. © 2002 American Institute of Physics.
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73.63.Rt Nanoscale contacts
73.23.Ad Ballistic transport
73.23.Ra Persistent currents
81.07.Lk Nanocontacts
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Band bending mechanism for field emission in wide-band gap semiconductors

R. Z. Wang, B. Wang, H. Wang, H. Zhou, A. P. Huang, M. K. Zhu, H. Yan, and X. H. Yan

Appl. Phys. Lett. 81, 2782 (2002); http://dx.doi.org/10.1063/1.1511809 (3 pages) | Cited 25 times

Online Publication Date: 30 September 2002

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A theoretical model based on the band bending theory was developed for explaining the field-emission mechanism of wide-band gap semiconductors (WBGSs). It was shown that the maximum value of the band bending, which is nearly linearly proportional to the band gap of WBGSs, may amount to a few eV. Furthermore, the calculated field-emission energy distribution combined with the band bending analyzed on cubic boron nitride (c-BN) as typical one of WBGSs, indicated that the electron emission originates from the conduction band minimum resulting from the band bending. These results present a perspective to explain the field-emission mechanism, in which it is considered that the band bending, as well as the negative electron affinity, is of equal importance to the excellent field emission performances of WBGSs. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
71.20.Nr Semiconductor compounds
81.05.Ea III-V semiconductors

Thermal and doping dependence of 4H-SiC polytype transformation

L. J. Brillson, S. Tumakha, G. H. Jessen, R. S. Okojie, M. Zhang, and P. Pirouz

Appl. Phys. Lett. 81, 2785 (2002); http://dx.doi.org/10.1063/1.1512816 (3 pages) | Cited 19 times

Online Publication Date: 30 September 2002

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We have observed characteristic temperatures, anneal times, and doping densities that lead to stacking faults and 3C-SiC-like bands in 4H-SiC epilayers. Low energy cathodoluminescence spectroscopy measurements reveal a temperature threshold of 800 °C for emergence of these features in thermally oxidized or argon annealed 4H-SiC with an activation energy ≈2.5 eV. Stacking fault generation and polytype transformation exhibits a strong doping dependence, appearing only in a range of highly doped n-type 4H-SiC. Systematics of these strain and/or electronic effects induced by high N concentrations can be used to control structural instabilities during SiC device fabrication. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
64.70.K- Solid-solid transitions
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Cc Kinetics of defect formation and annealing
78.66.Li Other semiconductors
61.72.up Other materials
61.72.Nn Stacking faults and other planar or extended defects
81.65.Mq Oxidation

Relaxation of photoinjected spins during drift transport in GaAs

H. Sanada, I. Arata, Y. Ohno, Z. Chen, K. Kayanuma, Y. Oka, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 81, 2788 (2002); http://dx.doi.org/10.1063/1.1512818 (3 pages) | Cited 34 times

Online Publication Date: 30 September 2002

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We studied the transport of photoinjected spins in GaAs by time-resolved photoluminescence measurements. At low temperatures, the spin polarization after drift transport of 4 μm is found to decrease as the applied electric field E increases to a few kV/cm, and it disappears when E exceeds 3 kV/cm. The origin of the field-dependent spin relaxation is discussed. © 2002 American Institute of Physics.
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72.25.Dc Spin polarized transport in semiconductors
72.25.Rb Spin relaxation and scattering
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors

Coherent generation of 100 GHz acoustic phonons by dynamic screening of piezoelectric fields in AlGaN/GaN multilayers

E. Makarona, B. Daly, J.-S. Im, H. Maris, A. Nurmikko, and Jung Han

Appl. Phys. Lett. 81, 2791 (2002); http://dx.doi.org/10.1063/1.1512821 (3 pages) | Cited 14 times

Online Publication Date: 30 September 2002

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Ultrashort pulse laser techniques have been used to observe and characterize the generation of coherent phonons by rapid screening of strain-induced piezoelectric polarization fields in AlGaN/GaN multilayers. The results are compared with those where coherent phonons are launched by optical techniques without the carrier injections process to show consistency with the anticipated longitudinal phonon dispersion in the nitride semiconductor samples. © 2002 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
77.65.Ly Strain-induced piezoelectric fields
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.21.Ac Multilayers
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Energy relaxation during hot-exciton transport in quantum wells: Direct observation by spatially resolved phonon-sideband spectroscopy

Hui Zhao, Sebastian Moehl, and Heinz Kalt

Appl. Phys. Lett. 81, 2794 (2002); http://dx.doi.org/10.1063/1.1512819 (3 pages) | Cited 10 times

Online Publication Date: 30 September 2002

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We investigate the energy relaxation of excitons during the real-space transport in ZnSe quantum wells by using microphotoluminescence with spatial resolution enhanced by a solid immersion lens. The spatial evolution of the LO-phonon sideband, originating from the LO-phonon assisted recombination of hot excitons, is measured directly. By calculating the LO-phonon assisted recombination probability, we obtain the nonthermal energy distribution of excitons and observe directly the energy relaxation of hot excitons during their transport. We find the excitons remain hot during their transport on a length scale of several micrometers. Thus, the excitonic transport on this scale cannot be described by classical diffusion. © 2002 American Institute of Physics.
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73.21.Fg Quantum wells
71.35.Gg Exciton-mediated interactions
78.67.De Quantum wells
63.20.kk Phonon interactions with other quasiparticles
78.55.Et II-VI semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Analysis of piezoresistance in n-type β-SiC for high-temperature mechanical sensors

Toshiyuki Toriyama and Susumu Sugiyama

Appl. Phys. Lett. 81, 2797 (2002); http://dx.doi.org/10.1063/1.1513652 (3 pages) | Cited 12 times

Online Publication Date: 30 September 2002

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Piezoresistance in n-type β-SiC was analyzed on the basis of electron transfer and mobility shift mechanisms for cubic many-valley semiconductors. Gauge factors were calculated by using shear deformation potential constant Ξu. The calculation was compared with experimental results taken from the literature. It was shown that incorporation of the electron transfer and the mobility shift mechanisms gives reasonable interpretation for piezoresistance in n-type β-SiC within the temperature range from 300 to 673 K, and impurity concentration range from 1018 to 1020 cm−3. These conditions correspond to typical operation ranges of high-temperature piezoresistive sensors. The effect of the intervalley scattering on piezoresistance can be neglected from the evidence that gauge factor is inversely proportional to temperature within the abovementioned conditions. © 2002 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
72.20.Fr Low-field transport and mobility; piezoresistance
43.38.Fx Piezoelectric and ferroelectric transducers
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems

Local electronic structures of GaMnAs observed by cross-sectional scanning tunneling microscopy

T. Tsuruoka, N. Tachikawa, S. Ushioda, F. Matsukura, K. Takamura, and H. Ohno

Appl. Phys. Lett. 81, 2800 (2002); http://dx.doi.org/10.1063/1.1512953 (3 pages) | Cited 22 times

Online Publication Date: 30 September 2002

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Using cross-sectional scanning tunneling microscopy (STM), we have investigated the local electronic properties of molecular-beam epitaxy grown GaMnAs layers on a p-GaAs substrate. The STM image shows light and dark areas with the average size on the order of nm. From conductance spectra measured with the STM, the bandgap of the GaMnAs is estimated to be 1.23±0.05 eV. An apparent conductance within the bandgap indicates the presence of hole states in the valence band, which are induced by Mn acceptors. A conductance peak at 0.7 eV above the valence band edge can be identified with electron tunneling into the ionization levels of As antisites. © 2002 American Institute of Physics.
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71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
61.72.J- Point defects and defect clusters
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
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