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1 Oct 2003

Volume 94, Issue 7, pp. 4241-4731

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Influence of the polarization on interfacial properties in Al/SiO2/GaN/Al0.4Ga0.6N/GaN heterojunction metal–insulator–semiconductor structures

P. Chen, S. J. Chua, W. D. Wang, D. Z. Chi, Z. L. Miao, and Y. D. Zheng

J. Appl. Phys. 94, 4702 (2003); http://dx.doi.org/10.1063/1.1599046 (3 pages) | Cited 4 times

Online Publication Date: 17 September 2003

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GaN-based metal–insulator–semiconductor (MIS) structures were fabricated by depositing a SiO2 film on a metalorganic chemical vapor deposition-grown GaN/Al0.4Ga0.6N/GaN double heterojunction. Various-frequency capacitance–voltage (C−V) measurements were carried out on the MIS structures. The measured C−V curves show a notable flatband shift of up to about 12.5 V with a typical polarization hysteresis window (9.4 V in width). Moreover, the capacitance of the heterojunction MIS structure reaches a minimum value under 4.1 V bias (forward scan) or −6.5 V bias (reverse scan). Due to the strong polarization and piezoelectric effects existing in AlGaN/GaN heterostructures, these results are deemed to be due to the influence of the piezoelectricity and polarization effects in the structure. Conductance–voltage (G−V) measurements were also performed. Various-frequency C−V and the G−V behaviors indicate that interface states have little influence on the sample. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants

Influence of band folding in InAs/GaSb superlattices

M. L. Tilton and G. C. Dente

J. Appl. Phys. 94, 4705 (2003); http://dx.doi.org/10.1063/1.1603960 (3 pages) | Cited 1 time

Online Publication Date: 17 September 2003

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We demonstrate the importance of accurate full zone fits for the band diagrams of constituent materials in the superlattice empirical pseudopotential method (SEPM) modeling of InAs/GaSb type-II strained superlattices. In particular, we show that inaccurate fits to X-valley energies in the constituent GaSb conduction band can lead to significant errors in the prediction of the primary band gaps of these superlattices. Specifically, we examine a set of five samples, each with a fixed InAs layer thickness of six monolayers. These samples show a strong blueshift of the band gap as the GaSb layer thickness is systematically increased. We demonstrate that the superlattice-induced band folding of the GaSb conduction band X valley significantly influences our theoretically predicted results for the shorter-period superlattice samples. This result helps shed light on the proper domain of application of heterostructure theories, such as effective mass theories, that only involve zone center properties of the constituent materials. © 2003 American Institute of Physics.
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73.21.Cd Superlattices
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Low-loss optical planar waveguides in YVO4 produced by silicon ion implantation at low doses

Feng Chen, Xue-Lin Wang, Shi-Ling Li, Gang Fu, Ke-Ming Wang, Qing-Ming Lu, Ding-Yu Shen, Rui Nie, and Hong-Ji Ma

J. Appl. Phys. 94, 4708 (2003); http://dx.doi.org/10.1063/1.1604965 (3 pages) | Cited 5 times

Online Publication Date: 17 September 2003

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Planar waveguides in x-cut YVO4 crystals were produced by ion-implanted Si+ ions with energies from 2.6 to 3.0 MeV at doses of 1×1013−1.5×1014 ions/cm2. The number of propagation modes varied from 1 to 3 as the doses of the implanted ions increased. The effective refractive indices of all the observed waveguide modes were higher than the refractive index of the substrate, which meant an index-enhanced guiding layer with thickness of ∼2 μm formed to confine the light propagation. The minimum propagation loss of the measured YVO4 waveguide was 0.27 dB/cm after annealing under suitable conditions. © 2003 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
61.72.up Other materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

Molecular Coulomb islands for single-electron tunneling in SiO2/molecular layer/SiO2 multilayers on Si(100)

Y. Wakayama, T. Kubota, H. Suzuki, T. Kamikado, and S. Mashiko

J. Appl. Phys. 94, 4711 (2003); http://dx.doi.org/10.1063/1.1605249 (3 pages) | Cited 11 times

Online Publication Date: 17 September 2003

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We demonstrate the Coulomb blockade phenomenon by using organic molecules as Coulomb islands embedded in a metal–oxide–semiconductor structure. Staircases in current–voltage (I–V) curves are observed in an SiO2/fullerene(C60)/SiO2 multilayered structure on Si (100) substrates. The staircases in the I–V curves can be attributed to the Coulomb blockade. The fullerenes serve as Coulomb islands and the SiO2 layers serve as tunneling barriers. The same multilayered structure that includes a porphyrin derivative also exhibits similar staircases in an I–V curve. These results reveal the potential of molecules to act as Coulomb islands of single-electron tunneling devices. © 2003 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.61.Wp Fullerenes and related materials

Effect of chemical substitution on the electronic properties of highly aligned thin films of Sr2−xAxFeMoO6 (A=Ca, Ba, La; x=0, 0.1)

W. R. Branford, S. K. Clowes, Y. V. Bugoslavsky, Y. Miyoshi, L. F. Cohen, A. V. Berenov, J. L. MacManus-Driscoll, J. Rager, and S. B. Roy

J. Appl. Phys. 94, 4714 (2003); http://dx.doi.org/10.1063/1.1604477 (3 pages) | Cited 10 times

Online Publication Date: 17 September 2003

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Highly aligned films of composition Sr1.9A0.1FeMoO6 (A=Ca,Ba,La) and undoped control samples, were fabricated on (100) single-crystal LaAlO3 by ultrasonic spray pyrolysis. Compared to undoped films, the doped films showed reduced saturation magnetization and magnetoresistance and the lanthanum-doped film showed a significant increase (∼40 K) in the Curie temperature. The electrical resistivity was well described by a spin-dependent transport model for all the films. The transport spin polarization has been determined with this model, and independently by point contact Andreev reflection spectroscopy. The doped films do not have improved polarization over the undoped films and the maximum P obtained is of the order of 63%. © 2003 American Institute of Physics.
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75.47.Pq Other materials
72.25.Dc Spin polarized transport in semiconductors
73.61.Le Other inorganic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Rs Spray coating techniques
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors

Optical properties of molecular beam epitaxy-grown Zn1−xMnxTe thin films measured by complementary techniques

F. C. Peiris, B. A. Kowalski, X. Liu, U. Bindley, and J. K. Furdyna

J. Appl. Phys. 94, 4717 (2003); http://dx.doi.org/10.1063/1.1600522 (3 pages) | Cited 5 times

Online Publication Date: 17 September 2003

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By using a combination of prism coupler, reflectivity, and spectroscopic ellipsometry techniques, we have determined the dielectric function of a series of molecular beam epitaxy-grown Zn1−xMnxTe thin films. These results have enabled us to determine the critical point parameters that correspond to the electronic transitions in the Brillouin zone for this particular alloy family. We find that, although the fundamental band gap E0 increases with x for this alloy, E1 and E1+Δ1 transition energies decrease with x for the Zn1−xMnxTe system, in contrast to most other zinc-blende semiconductor alloys. © 2003 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
68.55.-a Thin film structure and morphology
78.20.-e Optical properties of bulk materials and thin films

High quality type II InAs/GaSb superlattices with cutoff wavelength ∼3.7 μm using interface engineering

Yajun Wei, Junjik Bae, Aaron Gin, Andrew Hood, Manijeh Razeghi, Gail J. Brown, and Meimei Tidrow

J. Appl. Phys. 94, 4720 (2003); http://dx.doi.org/10.1063/1.1606506 (3 pages) | Cited 18 times

Online Publication Date: 17 September 2003

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We report the most recent advance in the area of type II InAs/GaSb superlattices that have cutoff wavelength of ∼3.7 μm. With GaxIn1−x type interface engineering techniques, the mismatch between the superlattices and the GaSb (001) substrate has been reduced to <0.1%. There is no evidence of dislocations using the best examination tools of x-ray, atomic force microscopy, and transmission electron microscopy. The full width half maximum of the photoluminescence peak at 11 K was ∼4.5 meV using an Ar+ ion laser (514 nm) at fluent power of 140 mW. The integrated photoluminescence intensity was linearly dependent on the fluent laser power from 2.2 to 140 mW at 11 K. The temperature-dependent photoluminescence measurement revealed a characteristic temperature of one T1=245 K at sample temperatures below 160 K with fluent power of 70 mW, and T1=203 K for sample temperatures above 180 K with fluent power of 70 and 420 mW. © 2003 American Institute of Physics.
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68.65.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)

Spin injection at Heusler/semiconductor interfaces: First-principles determination of potential discontinuity and half-metallicity

S. Picozzi, A. Continenza, and A. J. Freeman

J. Appl. Phys. 94, 4723 (2003); http://dx.doi.org/10.1063/1.1608469 (3 pages) | Cited 36 times

Online Publication Date: 17 September 2003

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Technologically relevant properties, such as potential discontinuity and half-metallic behavior, are determined by means of an accurate first-principles approach for Co2MnGe/GaAs and Co2MnGe/Ge interfaces. Interface states appear in both sides of the junctions, so that half-metallicity, typical of bulk Co2MnGe, is locally lost. As for the potential discontinuity, the character of the contact is dramatically affected by the semiconductor side: In Co2MnGe/GaAs, irrespective of the atomic termination, the Fermi level is pinned within the energy band gap, whereas it lies close to the valence-band maximum in the case of Co2MnGe/Ge. This gives rise to a rectifying contact in the first case and ohmic for holes in the second case, both potentially useful for spin–injection purposes. Finally, we investigate the effects of possible Co–Mn antisites in bulk Co2MnGe and find that half-metallicity is only locally destroyed, since defect-induced gap states are shown to be screened in a couple of nearest-neighbor atomic shells. © 2003 American Institute of Physics.
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72.25.Hg Electrical injection of spin polarized carriers
73.40.Ns Metal-nonmetal contacts
71.15.-m Methods of electronic structure calculations
73.20.At Surface states, band structure, electron density of states
61.72.J- Point defects and defect clusters
75.50.Cc Other ferromagnetic metals and alloys

Giant magnetoresistance in Mn2−xCuxSb (x⩽0.4) compounds

Y. Q. Zhang, Z. D. Zhang, D. K. Xiong, W. F. Li, and J. He

J. Appl. Phys. 94, 4726 (2003); http://dx.doi.org/10.1063/1.1608468 (3 pages) | Cited 2 times

Online Publication Date: 17 September 2003

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Magnetic and magnetotransport properties of Mn2−xCuxSb (x=0, 0.1, 0.2, and 0.4) compounds have been studied. A phase transition from a ferrimagnetic to an antiferromagnetic state occurs in the Cu-substituted compounds as the temperature is reduced. A magnetic field-driven transition takes place in the Cu-containing compounds, changing the spin configuration from antiferromagnetic to ferromagnetic. The giant magnetoresistance effect is observed in these compounds, accompanying the transition. The largest magnetoresistance ratio of −40% is observed for Mn1.9Cu0.1Sb at 170 K in a magnetic field of 5 T. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics
75.30.Wx Spin crossover
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Carbazole-functionalized europium complex and its high-efficiency organic electroluminescent properties

H. Xin, F. Y. Li, M. Guan, C. H. Huang, M. Sun, K. Z. Wang, Y. A. Zhang, and L. P. Jin

J. Appl. Phys. 94, 4729 (2003); http://dx.doi.org/10.1063/1.1608467 (3 pages) | Cited 37 times

Online Publication Date: 17 September 2003

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A complex tris(dibenzoylmethanato){1-ethyl-2-(N-ethyl-carbazole-yl-4) imidazo[4,5-f]1,10phenanthroline} europium(III) [Eu(DBM)3phencarz] functionalized by a hole-transport group carbazole was synthesized. Devices using this complex as emitter showed greatly enhanced performance benefited from the increased hole-transport properties and efficient energy transfer from carbazole to the central ions. A 58-nm-single-layer device gave a brightness of 20 cd/m2 at 15 V. The highest power efficiency of 2.7 lm/W at 5 V and 0.5 cd/m2 and the luminance exceeding 2000 cd/m2 at 20 V was obtained from a device with the configuration of ITO/TPD(20 nm)/Eu(DBM)3phencarz(40 nm)/BCP(20 nm)/AlQ(40 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm). © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
85.60.Jb Light-emitting devices
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