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29 Sep 2008

Volume 93, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 93, 132101 (2008); http://dx.doi.org/10.1063/1.2988720 (3 pages)

Yueh-Nan Chen and Lukas Gilz
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Proposal for observation of retardation effect between two quantum dots via current noise

Yueh-Nan Chen and Lukas Gilz

Appl. Phys. Lett. 93, 132101 (2008); http://dx.doi.org/10.1063/1.2988720 (3 pages)

Online Publication Date: 29 September 2008

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We propose to observe the retardation effect between two quantum dots in a one-dimensional waveguide. The effect of retardation is more pronounced comparing to that in free space. If the photons are to be reflected by a mirror at one of the ends, the interference role played by the reflecting photon is found to be destructive. With the combination of p-i-n junction, the retardation effect can be read out via current-noise spectrums.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.79.Gn Optical waveguides and couplers

Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass

S. Dasgupta, S. Birner, C. Knaak, M. Bichler, A. Fontcuberta i Morral, G. Abstreiter, and M. Grayson

Appl. Phys. Lett. 93, 132102 (2008); http://dx.doi.org/10.1063/1.2991448 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2008

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We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and observed transport evidence of single anisotropic-mass valley occupancy for the electrons in a 150 Å wide QW. Our calculations of strain and quantum confinement for these samples predict single anisotropic-mass valley occupancy for well widths W greater than 53 Å. Below this, double-valley occupation is predicted such that the longitudinal mass axes are collinear. We observed mobility anisotropy in the electronic transport along the crystallographic directions in the ratio of 2.8, attributed to the mass anisotropy as well as anisotropic scattering of the electrons in the X-valley of AlAs.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
72.20.Fr Low-field transport and mobility; piezoresistance
81.05.Ea III-V semiconductors
81.07.St Quantum wells

Achieving high Curie temperature in (Ga,Mn)As

M. Wang, R. P. Campion, A. W. Rushforth, K. W. Edmonds, C. T. Foxon, and B. L. Gallagher

Appl. Phys. Lett. 93, 132103 (2008); http://dx.doi.org/10.1063/1.2992200 (3 pages) | Cited 42 times

Online Publication Date: 29 September 2008

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We study the effects of growth temperature, Ga:As ratio, and postgrowth annealing procedure on the Curie temperature TC of (Ga,Mn)As layers grown by molecular beam epitaxy. We achieve the highest TC values for growth temperatures very close to the two-dimensional–three-dimensional phase boundary. The increase in TC, due to the removal of interstitial Mn by postgrowth annealing, is counteracted by a second process, which reduces TC and which is more effective at higher annealing temperatures. Our results show that it is necessary to optimize the growth parameters and postgrowth annealing procedure to obtain the highest TC.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors

Carrier transport mechanisms of nonvolatile memory devices based on nanocomposites consisting of ZnO nanoparticles with polymethylmethacrylate nanocomposites sandwiched between two C60 layers

Kyu Ha Park, Jae Hun Jung, Fushan Li, Dong Ick Son, and Tae Whan Kim

Appl. Phys. Lett. 93, 132104 (2008); http://dx.doi.org/10.1063/1.2992203 (3 pages) | Cited 10 times

Online Publication Date: 29 September 2008

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Transmission electron microscope images showed that ZnO nanoparticles were formed in a polymethylmethacrylate (PMMA) layer. Current-voltage (I-V) curves for the Al/C60/ZnO nanoparticles embedded in the PMMA layer/C60/indium tin oxide (ITO) device at 300 K showed a current bistability with a large on/off ratio of 104, which was much larger than the on/off ratio of the device without C60 layers, indicative of significant enhancement of memory storage. Carrier transport mechanisms of the memory effects for the Al/C60/ZnO nanoparticles embedded in the PMMA layer/C60/ITO device are described on the basis of the I-V results.
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84.30.Sk Pulse and digital circuits

Enhanced oscillator strength of interband transitions in coupled Ge/Si quantum dots

A. I. Yakimov, A. A. Bloshsin, and A. V. Dvurechenskii

Appl. Phys. Lett. 93, 132105 (2008); http://dx.doi.org/10.1063/1.2988469 (3 pages) | Cited 8 times

Online Publication Date: 30 September 2008

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We report a calculation of oscillator strength for the Δ1−Γ25′ interband transition in two vertically coupled pyramidal Ge quantum dots embedded in Si. A six-band k⋅p formalism was used to study the Γ25′ hole states, and a single-band approach was used to obtain the Δ1 electron state interacting with the hole. The elastic strain due to the lattice mismatch between Ge and Si was included into the problem via the Bir–Pikus Hamiltonian. We find that when two dots are brought closely together, the oscillator strength may enlarge by a factor of about 2 as compared to the single-dot system.
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73.21.La Quantum dots
71.15.-m Methods of electronic structure calculations

Fabrication and microstructure of p-type transparent conducting CuS thin film and its application in dye-sensitized solar cell

K. D. Yuan, J. J. Wu, M. L. Liu, L. L. Zhang, F. F. Xu, L. D. Chen, and F. Q. Huang

Appl. Phys. Lett. 93, 132106 (2008); http://dx.doi.org/10.1063/1.2991441 (3 pages) | Cited 16 times

Online Publication Date: 30 September 2008

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By reducing film thickness to a few nanometers, the narrow-band-gap CuS turns highly transparent. Surface modification by a self-assembled monolayer is the key factor to obtain a thin, dense, and continuous film. The film growth mechanism is identified as “layer-by-layer growth followed by islanding.” After annealing, a p-type conductivity of ∼ 2×103 S cm−1 is achieved at room temperature, and the thinnest conductive film has an average transparency of 92% between 400 and 800 nm. Using p-type CuS films as front contact layers, a dye-sensitized solar cell was fabricated with a significant photoelectric response.
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81.16.Dn Self-assembly
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.40.+w Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion

Carbon clusters in N-doped ZnO by metal-organic chemical vapor deposition

Kun Tang, Shulin Gu, Shunming Zhu, Wei Liu, Jiandong Ye, Jianmin Zhu, Rong Zhang, Youdou Zheng, and Xiaowei Sun

Appl. Phys. Lett. 93, 132107 (2008); http://dx.doi.org/10.1063/1.2992197 (3 pages) | Cited 14 times

Online Publication Date: 30 September 2008

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We employed transmission electron microscopy and Raman spectra to investigate the behavior of impurity carbon usually unintentionally introduced in N-doped ZnO by metal-organic chemical vapor deposition. Unintentional doped carbon may form graphite clusters along grain boundaries resulting in n-type domains and possibly be a big obstacle for the realization of p-type conductivity. The enhanced desorption rate of hydrocarbon radicals by high temperature and oxygen atom will significantly suppress carbon incorporation rate. The results provide understandings of the formation mechanism of carbon clusters and help us find some available routines to minimize carbon impurity for realization of p-type N-doped ZnO.
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61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
61.72.Mm Grain and twin boundaries
68.43.Nr Desorption kinetics
78.30.Fs III-V and II-VI semiconductors

Carrier wave-packet transport under the influence of charged quantum dot in small-area resonant tunneling diode

Y. Hou, W.-P. Wang, N. Li, W.-L. Xu, W. Lu, and Y. Fu

Appl. Phys. Lett. 93, 132108 (2008); http://dx.doi.org/10.1063/1.2993339 (3 pages) | Cited 4 times

Online Publication Date: 30 September 2008

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It was shown experimentally that charging InAs quantum dots (QDs) embedded in a small-area GaAs/AlAs double-barrier resonant tunneling diode (RTD) effectively modified the carrier transport properties of the RTD. By adopting and comparing the one-dimensional plane-wave and three-dimensional (3D) wave-packet transport theories we show that the electron transports in the QDRTD device are in the form of 3D wave packets, which are strongly affected by the 3D long-range Coulomb potential induced by charged InAs QDs. This explains well experimental data and indicates that the 3D wave-packet transport model is more appropriate for the QDRTD device.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Electrical properties of Ta-doped SnO2 thin films epitaxially grown on TiO2 substrate

H. Toyosaki, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 93, 132109 (2008); http://dx.doi.org/10.1063/1.2993346 (3 pages) | Cited 13 times

Online Publication Date: 30 September 2008

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We report electrical properties of Ta-doped SnO2 (Sn1−xTaxO2) films epitaxially grown on (110) surfaces of rutile TiO2 single crystalline substrates by a pulsed laser deposition method. Due to the large in-plane lattice mismatches (3.0% along [math10] and 7.7% along [001]), the films had almost relaxed crystalline structure. With increasing x, electron density was systematically enhanced to undergo the insulator-metal transition between x = 0.0004 and 0.004. Sn0.95Ta0.05O2 films exhibited the resistivity as low as 1.1×10−4 Ω cm that is comparable to the lowest value for an epitaxial In2O3 film doped with Sn.
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73.61.Le Other inorganic semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
68.55.ag Semiconductors

High quality GaN-based Schottky barrier diodes

K. H. Lee, S. J. Chang, P. C. Chang, Y. C. Wang, and C. H. Kuo

Appl. Phys. Lett. 93, 132110 (2008); http://dx.doi.org/10.1063/1.2993353 (3 pages) | Cited 6 times

Online Publication Date: 30 September 2008

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We report the fabrication of GaN-based Schottky barrier diodes with multi-MgxNy/GaN buffer. Compared to conventional devices with a low-temperature GaN buffer, we achieved a six orders of magnitude smaller leakage current. It was also found that effective Schottky barrier height is larger for the proposed device due to the reduction in surface defect density by using the multi-MgxNy/GaN buffer.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions

Resonant and phonon-assisted tunneling transport through silicon quantum dots embedded in SiO2

B. Berghoff, S. Suckow, R. Rölver, B. Spangenberg, H. Kurz, A. Dimyati, and J. Mayer

Appl. Phys. Lett. 93, 132111 (2008); http://dx.doi.org/10.1063/1.2992057 (3 pages) | Cited 3 times

Online Publication Date: 1 October 2008

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Charge transport through SiO2/Si/SiO2 double-barrier structures (DBSs) and SiO2 single-barrier structures is investigated by low temperature I-V measurements. Resonant tunneling signatures accompanied by a negative differential conductance are observed if silicon quantum dots (Si QDs) are embedded in the amorphous SiO2 matrix. The I-V characteristics are correlated with the morphology of Si QDs extracted from transmission electron microscopy and photoluminescence. Evidence for phonon-assisted tunneling at low voltages has been found in the DBSs. These results show the potential but also the limitation for charge extraction from Si QDs embedded in SiO2.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.55.Ap Elemental semiconductors
73.63.Kv Quantum dots
78.67.Hc Quantum dots
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

High temperature electron spin relaxation in bulk GaAs

S. Oertel, J. Hübner, and M. Oestreich

Appl. Phys. Lett. 93, 132112 (2008); http://dx.doi.org/10.1063/1.2993344 (3 pages) | Cited 19 times

Online Publication Date: 1 October 2008

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Temperature and electron density dependent measurements of the electron spin relaxation in bulk GaAs are performed using time- and polarization-resolved photoluminescence spectroscopy. The electron spin relaxation time is dominated in the high temperature regime by the D’yakonov-Perel’ [ M. I. D’yakonov and V. I. Perel’, Sov. Phys. Solid State 13, 3023 (1972) ] spin relaxation mechanism and decreases for negligible electron densities from 42 ps at 300 K to 20 ps at 400 K. The measured spin relaxation times are compared with numerical calculations which include electron-phonon momentum scattering and have no adjustable parameters.
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72.25.Rb Spin relaxation and scattering
72.25.Fe Optical creation of spin polarized carriers
72.25.Dc Spin polarized transport in semiconductors
78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence

Dominant ultraviolet light emissions in packed ZnO columnar homojunction diodes

Jieying Kong, Sheng Chu, Mario Olmedo, Lin Li, Zheng Yang, and Jianlin Liu

Appl. Phys. Lett. 93, 132113 (2008); http://dx.doi.org/10.1063/1.2992629 (3 pages) | Cited 22 times

Online Publication Date: 2 October 2008

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The growth of Sb-doped p-type ZnO/Ga-doped n-type ZnO homojunction on Si (100) substrate by molecular beam epitaxy led to closely packed vertical ZnO columns with lateral diameters ranging from 100 to 400 nm. Mesa structures were defined and Ohmic contact of both n-type ZnO and p-type ZnO was realized with Au/Ti and Au/NiO, respectively. I-V and C-V curves present typical electrical properties of a diode, indicating that reliable p-type ZnO was formed. Electroluminescence shows dominant ultraviolet emissions with insignificant deep-level related yellow/green band emissions at different drive currents from 60 to 100 mA at room temperature.
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85.30.Kk Junction diodes
85.60.Jb Light-emitting devices

Spin-splitting in an AlxGa1−xN/GaN nanowire for a quantum-ring interferometer

Ikai Lo, Wen-Yuan Pang, Yen-Liang Chen, Yu-Chi Hsu, Jih-Chen Chiang, Wei-Hsin Lin, Wan-Ting Chiu, Jenn-Kai Tsai, and Chun-Nan Chen

Appl. Phys. Lett. 93, 132114 (2008); http://dx.doi.org/10.1063/1.2995866 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2008

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An Al0.18Ga0.82N/GaN heterostructure was used to fabricate a ballistic nanowire with a wire width of 200 nm by focused ion beam. We observed the beating Shubnikov–de Haas oscillations in the nanowire with a spin-splitting energy of (2.4±0.3) meV. Based on the results, we proposed a spin-Hall quantum-ring interferometer made of AlxGa1−xN/GaN nanowires for spintronic applications.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Electrical properties of aggregated detonation nanodiamonds

Mose Bevilacqua, Sameer Patel, Aysha Chaudhary, Haitao Ye, and Richard B. Jackman

Appl. Phys. Lett. 93, 132115 (2008); http://dx.doi.org/10.1063/1.2996026 (3 pages) | Cited 6 times

Online Publication Date: 3 October 2008

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Nanometer-scale diamonds formed using a detonation process are an interesting class of diamond materials. Commercially supplied material is highly aggregated with ∼ 5 nm diamond crystals forming particles with micron sizes. Previous models have suggested that nondiamond carbon is incorporated between the crystals, which would reduce the electrical and chemical usefulness of this form of diamond. However, using impedance spectroscopy we have shown that at temperatures below 350 °C the form of detonation nanodiamond being studied is a near to ideal dielectric, implying a full sp3 form. At temperatures above this the surfaces of the diamond crystals may support some nondiamond carbon.
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72.80.Rj Fullerenes and related materials
81.07.Bc Nanocrystalline materials
81.05.U- Carbon/carbon-based materials

Electron scatterings in selectively doped n-AlGaAs/GaAs heterojunctions with high density self-assembled InAlAs antidots

Takuya Kawazu and Hiroyuki Sakaki

Appl. Phys. Lett. 93, 132116 (2008); http://dx.doi.org/10.1063/1.2996414 (3 pages) | Cited 2 times

Online Publication Date: 3 October 2008

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The scattering processes of two-dimensional electrons are studied in selectively doped n-AlGaAs/GaAs heterojunctions where high density InAlAs anti dots are embedded in the vicinity of the GaAs channel. Mobilities μ are measured as a function of the electron concentrations Ns in two samples where the In1−xAlxAs antidots are grown with different Al contents (x ∼ 0.75 and 0.5). It is found that the Ns dependence of μ is strongly dependent on the Al content x of the embedded InAlAs dots, although their shapes and densities are almost same. The experimental data are well explained by theoretical models based on the surface profiles of the InAlAs dot layers.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.U- Doping and impurity implantation
73.21.La Quantum dots

Epitaxial ferromagnetic Fe3Si/Si(111) structures with high-quality heterointerfaces

K. Hamaya, K. Ueda, Y. Kishi, Y. Ando, T. Sadoh, and M. Miyao

Appl. Phys. Lett. 93, 132117 (2008); http://dx.doi.org/10.1063/1.2996581 (3 pages) | Cited 17 times

Online Publication Date: 3 October 2008

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To develop silicon-based spintronic devices, we have explored high-quality ferromagnetic Fe3Si/silicon (Si) structures. Using low-temperature molecular beam epitaxy at 130 °C, we realize the epitaxial growth of ferromagnetic Fe3Si layers on Si(111) with an abrupt interface, and the grown Fe3Si layer has the ordered DO3 phase. Measurements of magnetic and electrical properties for the Fe3Si/Si(111) yield a magnetic moment of ∼ 3.16μB/f.u. at room temperature and a rectifying Schottky-diode behavior with the ideality factor of ∼ 1.08, respectively.
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73.40.Ns Metal-nonmetal contacts
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.30.Cr Saturation moments and magnetic susceptibilities
73.40.Ei Rectification
85.30.Kk Junction diodes
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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