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11 Dec 2006

Volume 89, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 242109 (2006); http://dx.doi.org/10.1063/1.2405843 (3 pages)

Carlo R. da Cunha, Nobuyuki Aoki, Takahiro Morimoto, Yuichi Ochiai, Richard Akis, and David K. Ferry
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Resonant tunneling magnetoresistance in coupled quantum wells

Christian Ertler and Jaroslav Fabian

Appl. Phys. Lett. 89, 242101 (2006); http://dx.doi.org/10.1063/1.2402878 (3 pages) | Cited 17 times

Online Publication Date: 11 December 2006

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A three barrier resonant tunneling structure in which the two quantum wells are formed by a magnetic semiconductor is theoretically investigated. Self-consistent numerical simulations of the structure predict giant magnetocurrent in the resonant bias regime as well as significant current spin polarization for a considerable range of applied biases. The requirements for large magnetocurrent are spin resolved resonance levels as well as asymmetry (spatial or magnetic) of the coupled quantum wells.
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75.47.Pq Other materials
75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
72.25.Dc Spin polarized transport in semiconductors
85.75.Mm Spin polarized resonant tunnel junctions
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Magnetic properties of ZnMnO nanopowders solvothermally grown at low temperature from zinc and manganese acetate

A. Tomaszewska-Grzȩda, A. Opalińska, E. Grzanka, W. Łojkowski, A. Gedanken, M. Godlewski, S. Yatsunenko, V. Osinniy, and T. Story

Appl. Phys. Lett. 89, 242102 (2006); http://dx.doi.org/10.1063/1.2404599 (3 pages) | Cited 6 times

Online Publication Date: 11 December 2006

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The authors demonstrate that nanometer size ZnMnO nanopowders, grown from zinc and manganese (II) acetates at low temperatures under microwave radiation, are free of Mn clusters and the inclusion of Mn oxides. These nanopowders show a strong paramagnetic phase with only a weak antiferromagnetic contribution due to Mn–Mn interactions.
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81.05.Dz II-VI semiconductors
81.07.Wx Nanopowders
81.10.Dn Growth from solutions
75.20.Ck Nonmetals
75.50.Ee Antiferromagnetics
75.50.Pp Magnetic semiconductors

Field-effect transistor based on atomically flat rutile TiO2

Masao Katayama, Shinya Ikesaka, Jun Kuwano, Yuichi Yamamoto, Hideomi Koinuma, and Yuji Matsumoto

Appl. Phys. Lett. 89, 242103 (2006); http://dx.doi.org/10.1063/1.2404980 (3 pages) | Cited 18 times

Online Publication Date: 12 December 2006

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The authors have fabricated a field-effect transistor (FET) based on a rutile TiO2 active channel. Top-gate transistor structure with an amorphous LaAlO3 insulator was fabricated on the ultrasmoothed rutile single crystals. Reproducible n-type FET actions were observed only by the use of ultrasmoothed TiO2 surfaces. Moreover, an anisotropy of the field-effect mobility depending on the channel direction, which reflects intrinsic nature of rutile, was definitely observed. Inserting MgO insulating buffer between TiO2 and amorphous LaAlO3 suppressed the off-state current and realized on-to-off current ratio as high as 104.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Direct measurement of carrier drift velocity and mobility in a polymer field-effect transistor

Debarshi Basu, Liang Wang, Lawrence Dunn, Byungwook Yoo, Suvid Nadkarni, Ananth Dodabalapur, Martin Heeney, and Iain McCulloch

Appl. Phys. Lett. 89, 242104 (2006); http://dx.doi.org/10.1063/1.2405378 (3 pages) | Cited 11 times

Online Publication Date: 12 December 2006

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An electronic method to measure the drift velocity and mobility of charge carriers in polymer thin film transistor has been developed. The measurement is based on the movement of a packet of carriers injected into the channel. This technique can be used to explore trap states and therefore obtain a comprehensive understanding of charge transport in these materials. Drift mobility of 0.52 cm2/V s is obtained from the transit time which is a factor of 3 higher than the field-effect transistor mobility.
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85.30.Tv Field effect devices

Hysteresis in electric polarization of InP doped with Mn

C. S. Park and T. W. Kang

Appl. Phys. Lett. 89, 242105 (2006); http://dx.doi.org/10.1063/1.2405395 (3 pages) | Cited 4 times

Online Publication Date: 12 December 2006

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InP:Mn was grown by liquid phase epitaxy method. Ferroelectric characterization of the InMnP based capacitor revealed a clear hysteresis in its polarization-voltage curves. The remnant polarization of InP:Mn amounts to 3.84 μC/cm2 at 300 Hz. Current-voltage hysteresis demonstrated a variation of built-in voltage, and capacitance versus voltage revealed a hysteresis as well. Imprint, electric conductivity, and hysteretic asymmetry of sample were enhanced after annealing at 800 °C for 30 s. It is considered that the hysteresis is originated from the displacement of phosphorus vacancy by Jahn-Teller distortion of [MnIn−VP] complex defect.
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77.55.-g Dielectric thin films
73.61.Ey III-V semiconductors
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
61.72.Cc Kinetics of defect formation and annealing

Tunneling magnetoresistance of MnAs thin film/GaAs/AlAs/GaAs:MnAs nanoclusters and its AlAs barrier thickness dependence

Pham Nam Hai, Masafumi Yokoyama, Shinobu Ohya, and Masaaki Tanaka

Appl. Phys. Lett. 89, 242106 (2006); http://dx.doi.org/10.1063/1.2405399 (3 pages) | Cited 6 times

Online Publication Date: 12 December 2006

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The authors have investigated tunneling magnetoresistance (TMR) of magnetic tunnel junctions (MTJs) consisting of MnAs thin film (20 nm)/GaAs(1 nm)/AlAs(d = 2–5 nm)/GaAs:MnAs nanoclusters (10 nm). The GaAs:MnAs material contains ferromagnetic MnAs nanoclusters in a GaAs matrix and acts as a spin injector and a spin detector. They observed an oscillatory behavior of the TMR ratio with the increasing AlAs barrier thickness, which can be explained by the quantum interference of two X-valley related wave functions in the AlAs barrier.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
75.47.Pq Other materials
72.25.Mk Spin transport through interfaces
73.61.Ey III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Simple-layered high mobility field effect heterostructured two-dimensional electron device

R. L. Willett, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 89, 242107 (2006); http://dx.doi.org/10.1063/1.2403183 (3 pages) | Cited 6 times

Online Publication Date: 12 December 2006

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The authors present a two-dimensional electron heterostructure field effect device of simplistic design and ease of fabrication that displays high mobility electron transport. This is accomplished using a high efficacy contacting scheme and simple metallic overlapping gate, obviating dopant layers. The resultant devices demonstrate adjustable electron densities and mobilities larger than 8×106 cm2/V s at the highest densities of 2.4×1011/cm2. This device type provides an experimental avenue for studying electron correlations and may answer demands for routine fabrication of practical high electron mobility transistors.
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85.30.Tv Field effect devices

Influence of sample compaction on the thermoelectric performance of Zn4Sb3

B. L. Pedersen, H. Birkedal, B. B. Iversen, M. Nygren, and P. T. Frederiksen

Appl. Phys. Lett. 89, 242108 (2006); http://dx.doi.org/10.1063/1.2404612 (3 pages) | Cited 18 times

Online Publication Date: 12 December 2006

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Five compacted samples of thermoelectric Zn4Sb3 have been prepared from the same synthesis batch by spark plasma sintering. Four samples were made from powder with a grain size <45 μm, and one sample from powder with grain size >45 μm. Thermoelectric properties were evaluated, and an apparent strong correlation with sample density is found. ZnSb impurity contents obtained from powder x-ray diffraction cannot explain the variation in properties, which the authors’ suggest may be caused by slight changes in Zn content. The results show that minute changes in sample compaction conditions can have a larger effect on ZT than doping.
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81.05.Hd Other semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
61.72.S- Impurities in crystals
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Rs Electrical and magnetic properties related to treatment conditions

Imaging of quantum interference patterns within a quantum point contact

Carlo R. da Cunha, Nobuyuki Aoki, Takahiro Morimoto, Yuichi Ochiai, Richard Akis, and David K. Ferry

Appl. Phys. Lett. 89, 242109 (2006); http://dx.doi.org/10.1063/1.2405843 (3 pages) | Cited 12 times

Online Publication Date: 13 December 2006

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Visualization of quantum interference patterns has been obtained within a quantum point contact using scanning gate microscopy. The area distribution of the interference pattern is shown to be consistent with the interference area obtained from the magnetoconductance fluctuations of a quantum point contact. Both distributions follow the Gaussian unitary ensemble, corresponding to chaotic behavior. The interference is caused by the random potential fluctuations within the channel, which is modified by the tip-induced potential.
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73.23.-b Electronic transport in mesoscopic systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
85.35.Ds Quantum interference devices

Epitaxial semimetallic HfxZr1−xB2 templates for optoelectronic integration on silicon

Radek Roucka, YuJin An, Andrew V. G. Chizmeshya, John Tolle, John Kouvetakis, Vijay R. D'Costa, José Menéndez, and Peter Crozier

Appl. Phys. Lett. 89, 242110 (2006); http://dx.doi.org/10.1063/1.2403189 (3 pages) | Cited 2 times

Online Publication Date: 13 December 2006

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High quality heteroepitaxial HfxZr1−xB2 (x = 0–1) buffers were grown directly on Si(111). The compositional dependence of the film structure and ab initio elastic constants were used to show that hexagonal HfxZr1−xB2 possess tensile in-plane strain (0.5%) as grown. High quality HfB2 films were also grown on strain compensating ZrB2-buffered Si(111). Initial reflectivity measurements of thick ZrB2 films agree with first principles calculations which predict that the reflectivity of HfB2 increases by 20% relative to ZrB2 in the 2–8 eV range. These tunable structural, thermoelastic, and optical properties suggest that HfxZr1−xB2 templates should be suitable for broad integration of III nitrides with Si.
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68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Robust detection of hydrogen using differential AlGaN/GaN high electron mobility transistor sensing diodes

Hung-Ta Wang, T. J. Anderson, F. Ren, Changzhi Li, Zhen-Ning Low, Jenshan Lin, B. P. Gila, S. J. Pearton, A. Osinsky, and Amir Dabiran

Appl. Phys. Lett. 89, 242111 (2006); http://dx.doi.org/10.1063/1.2408635 (3 pages) | Cited 15 times

Online Publication Date: 13 December 2006

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The use of AlGaN/GaN high electron mobility transistor (HEMT) differential sensing diodes is shown to provide robust detection of 1% H2 in air at 25 °C. The active device in the differential pair is coated with 10 nm of Pt to enhance catalytic dissociation of molecular hydrogen, while the reference diode is coated with Ti/Au. The active diode in the pair shows an increase in forward current of several milliamperes at a bias voltage of 2.5 V when exposed to 1% H2 in air. The HEMT diodes show a response approximately twice that of GaN Schottky diodes, due to the presence of piezoelectric and spontaneous polarization in the heterostructure. The use of the differential pair removes false alarms due to ambient temperature variations.
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85.30.Tv Field effect devices
85.30.Kk Junction diodes

Piezoelectric fields in GaInN/GaN quantum wells on different crystal facets

M. Feneberg, F. Lipski, R. Sauer, K. Thonke, T. Wunderer, B. Neubert, P. Brückner, and F. Scholz

Appl. Phys. Lett. 89, 242112 (2006); http://dx.doi.org/10.1063/1.2405866 (3 pages) | Cited 30 times

Online Publication Date: 14 December 2006

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Direction and strength of piezoelectric built-in fields of GaInN quantum wells have been experimentally determined. The quantum wells have been grown either on the conventional {0001} crystal plane of GaN or on {1math01} facets of selectively grown GaN stripes. The emission peak position of the electric-field-dependent photoluminescence can be modeled and yields value and sign of the piezoelectric field dependent on the strain of the quantum wells. On the semipolar {1math01} facets, the quantum wells show a much weaker field (−0.1 MV/cm) compared to quantum wells grown on polar {0001} planes (−1.9 MV/cm), consistent with theoretic predictions.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
77.65.Ly Strain-induced piezoelectric fields

Thermally stimulated current studies on deep levels in hydrothermally grown single crystal ZnO bulk

K. Kuriyama, M. Ooi, K. Matsumoto, and K. Kushida

Appl. Phys. Lett. 89, 242113 (2006); http://dx.doi.org/10.1063/1.2405867 (3 pages) | Cited 9 times

Online Publication Date: 14 December 2006

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The evaluation of the deep levels in hydrothermally grown ZnO single crystal bulk is studied using a thermally stimulated current (TSC) method with excitation above (below) the band gap. Two broad TSC spectra are resolved by four traps, P1 (165 meV), P2 (255 meV), P3 (300 meV), and P4 (375 meV). P2, P3, and P4 traps are responsible for excitation by the blue and green lights, but P1 trap is weakly responsible. Possible origins of P1 and P2 are attributed to native point defects and Li acceptor, respectively. P3 is correlated to oxygen vacancy as an origin of the green luminescence.
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71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.J- Point defects and defect clusters

Tunnel magnetoresistance and robust room temperature exchange bias with multiferroic BiFeO3 epitaxial thin films

H. Béa, M. Bibes, S. Cherifi, F. Nolting, B. Warot-Fonrose, S. Fusil, G. Herranz, C. Deranlot, E. Jacquet, K. Bouzehouane, and A. Barthélémy

Appl. Phys. Lett. 89, 242114 (2006); http://dx.doi.org/10.1063/1.2402204 (3 pages) | Cited 61 times

Online Publication Date: 15 December 2006

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The authors report on the functionalization of multiferroic BiFeO3 epitaxial films for spintronics. A first example is provided by the use of ultrathin layers of BiFeO3 as tunnel barriers in magnetic tunnel junctions with La2/3Sr1/3MnO3 and Co electrodes. In such structures, a positive tunnel magnetoresistance up to 30% is obtained at low temperature. A second example is the exploitation of the antiferromagnetic spin structure of a BiFeO3 film to induce a sizable ( ∼ 60 Oe) exchange bias on a ferromagnetic film of CoFeB at room temperature. Remarkably, the exchange bias effect is robust upon magnetic field cycling, with no indications of training.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.30.Et Exchange and superexchange interactions
75.80.+q Magnetomechanical effects, magnetostriction
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Effect of thermal treatment on oxygen stoichiometry and transport properties of SrRuO3 thin films

Joe Sakai, Nobuaki Ito, Shin-Ichi Ito, Kenji Takahashi, and Hiroshi Funakubo

Appl. Phys. Lett. 89, 242115 (2006); http://dx.doi.org/10.1063/1.2408649 (3 pages) | Cited 4 times

Online Publication Date: 15 December 2006

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The oxygen content was evaluated using the non-Rutherford elastic resonant scattering method for SrRuO3 (SRO) thin films deposited on (001) SrTiO3 substrates by a sputtering technique, followed by postannealing in various conditions. The resistivity of the SRO film annealed in 50 mTorr Ar at 500 °C was not higher than 4×10−3 Ω cm in the range of 5–300 K despite its oxygen deficiency ( = 2.7). On the other hand, the SRO film annealed in an Ar+1% O2 mixture gas of 50 mTorr at 700 °C retained its oxygen stoichiometry and maintained its resistivity below 5×10−4 Ω cm.
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73.61.Ng Insulators
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.66.Bi Elemental solids
61.66.Dk Alloys
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Internal magnetic field in thin ZnSe epilayers

S. Ghosh, N. P. Stern, B. Maertz, D. D. Awschalom, G. Xiang, M. Zhu, and N. Samarth

Appl. Phys. Lett. 89, 242116 (2006); http://dx.doi.org/10.1063/1.2404600 (3 pages) | Cited 1 time

Online Publication Date: 15 December 2006

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Strain-induced spin splitting is observed and characterized using pump-probe Kerr rotation spectroscopy in n-ZnSe epilayers grown on GaAs substrates. The spin splitting energies are mapped out as a function of pump-probe separation, applied voltage, and temperature in a series of samples of varying epilayer thicknesses and compressive strain arising from epilayer-substrate lattice mismatch. The strain is independently quantified using photoluminescence and X-ray diffraction measurements. The authors observe that the magnitude of the spin splitting increases with applied voltage and temperature and is highly crystal direction dependent, vanishing along [1math0].
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71.70.Fk Strain-induced splitting
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Effect of the inversion layer on the electrical characterization of Pt germanide/n-Ge(001) Schottky contacts

H. B. Yao, D. Z. Chi, R. Li, S. J. Lee, and D.-L. Kwong

Appl. Phys. Lett. 89, 242117 (2006); http://dx.doi.org/10.1063/1.2408665 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2006

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Schottky contacts of Pt germanide films formed on n-Ge(001) through solid-state reaction between Pt and Ge(001) via rapid thermal annealing were investigated. Almost identical effective barrier heights of ∼ 0.619–0.626 eV were obtained for PtGe/n-Ge(001), Pt2Ge3/n−Ge(001), and PtGe2/n-Ge(001) Schottky contacts from current-voltage measurements. From the effective barrier height values, actual barrier heights of ∼ 0.653–0.663 eV were determined by taking into account the image force induced barrier lowering in the presence of strong inversion layers at the interfaces. The actual barrier height values obtained were further validated by the good agreement between experimental and simulation results for capacitance-voltage characterization.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
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