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3 May 2004

Volume 84, Issue 18, pp. 3435-3703

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3648 (2004); http://dx.doi.org/10.1063/1.1737470 (3 pages)

Jingbo Li and Lin-Wang Wang
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20 μm cutoff heterojunction interfacial work function internal photoemission detectors

S. G. Matsik, M. B. M. Rinzan, D. G. Esaev, A. G. U. Perera, H. C. Liu, and M. Buchanan

Appl. Phys. Lett. 84, 3435 (2004); http://dx.doi.org/10.1063/1.1634386 (3 pages) | Cited 6 times

Online Publication Date: 20 April 2004

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Results are reported on Heterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors designed for operation up to 20 μm. The peak response of 100 mA/W at 12.5 μm with a D∗ of 2×1011 Jones was observed with a cutoff wavelength of ∼20 μm. The BLIP temperature for the devices was 40 K at 1.5 V bias. While the peak response remained almost constant (∼95 mA/W) up to 40 K, the D∗ reduced to 5×109 Jones due to the increased dark current. The response increased with doping while the dark current did not change significantly. Hence, higher responsivity and D∗ can be expected for designs with higher doping. Designs utilizing increased reflection from the bottom contact are suggested to improve the resonant cavity enhancement for optimizing the detectors, which should lead to higher D∗ and BLIP temperature. © 2004 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
61.72.uj III-V and II-VI semiconductors
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Optical attenuation signatures of Bacillus subtillis in the THz region

E. R. Brown, J. E. Bjarnason, T. L. J. Chan, A. W. M. Lee, and M. A. Celis

Appl. Phys. Lett. 84, 3438 (2004); http://dx.doi.org/10.1063/1.1711167 (3 pages) | Cited 11 times

Online Publication Date: 20 April 2004

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This letter reports the use of a photomixing sweep oscillator to characterize samples of B. subtillis spores at room temperature between 200 and 1200 GHz. Dilute (10% by mass) and concentrated samples were tested, the former using fine-grained polyethylene powder as a low-loss dielectric matrix. The dilute sample displays many weak transmission undulations, but the three centered at 418, 1037 and 253 GHz were strong enough to remain after normalization. The concentrated sample displays a much stronger broadband attenuation, precluding accurate measurements above ∼500 GHz. Two broad signatures remain between 250 and 290 GHz, and between 410 and 440 GHz, respectively. The results suggest that single-bioparticle electromagnetic resonance, perhaps from surface phonons, occurs in the dilute sample but is smeared in the concentrated sample. © 2004 American Institute of Physics.
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87.50.W- Optical/infrared radiation effects
77.84.Jd Polymers; organic compounds
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Synthesis of uniform GaN quantum dot arrays via electron nanolithography of D2GaN3

P. A. Crozier, J. Tolle, J. Kouvetakis, and Cole Ritter

Appl. Phys. Lett. 84, 3441 (2004); http://dx.doi.org/10.1063/1.1736314 (3 pages) | Cited 34 times

Online Publication Date: 20 April 2004

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We demonstrate the deposition of periodic arrays of uniformly sized GaN quantum dots onto a SiOx substrate. The dots are deposited using a nanolithography technique based on a combination of electron-beam-induced chemical vapor deposition and single-source molecular hydride chemistries. Under appropriate deposition conditions, we can deposit uniform dots of height 5 nm and full widths at half-maxima of 4 nm. The dot size is controlled by the spatial distribution of secondary electrons leaving the substrate surface. The smallest, most uniform void-free dots are created via nanolithography of molecules adsorbed on the substrate surface. © 2004 American Institute of Physics.
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81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography
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One-dimensional ordered structure of α-sexithienyl on Cu(110)

Manabu Kiguchi, Shiro Entani, Koichiro Saiki, and Genki Yoshikawa

Appl. Phys. Lett. 84, 3444 (2004); http://dx.doi.org/10.1063/1.1736315 (3 pages) | Cited 13 times

Online Publication Date: 20 April 2004

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We have studied atomic structures of α-sexithienyl (6T) films grown on Cu(110) by near-edge x-ray absorption fine structure (NEXAFS). A one-dimensional (1D) ordered structure of 6T with its molecular long axis parallel to the Cu[001] direction could be fabricated by deposition at 300 K and subsequent annealing at 360 K. Polarization- and azimuth-dependent NEXAFS revealed the formation process of the 1D structure and showed the molecular orientation in the in-plane direction directly. We propose a method to obtain the orientation distribution function of molecules using NEXAFS. © 2004 American Institute of Physics.
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68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
78.70.Dm X-ray absorption spectra
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Impact of dislocations on minority carrier electron and hole lifetimes in GaAs grown on metamorphic SiGe substrates

C. L. Andre, J. J. Boeckl, D. M. Wilt, A. J. Pitera, M. L. Lee, E. A. Fitzgerald, B. M. Keyes, and S. A. Ringel

Appl. Phys. Lett. 84, 3447 (2004); http://dx.doi.org/10.1063/1.1736318 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2004

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The minority carrier lifetime of electrons (τn) in p-type GaAs double heterostructures grown on GaAs substrates and compositionally graded Ge/Si1−xGex/Si (SiGe) substrates with varying threading dislocation densities (TDDs) were measured at room temperature using time-resolved photoluminescence. The electron lifetimes for homoepitaxial GaAs and GaAs grown on SiGe (TDD ∼ 1×106 cm−2) with a dopant concentration of 2×1017 cm−3 were ∼ 21 and ∼ 1.5 ns, respectively. The electron lifetime measured on SiGe was substantially lower than the previously measured minority carrier hole lifetime (τp) of ∼ 10 ns, for n-type GaAs grown on SiGe substrates with a similar residual TDD and dopant concentration. The reduced lifetime for electrons is a consequence of their higher mobility, which yields an increased sensitivity to the presence of dislocations in GaAs grown on metamorphic buffers. The disparity in dislocation sensitivity for electron and hole recombination has significant implications for metamorphic III-V devices. © 2004 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.S- Impurities in crystals
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Piezoelectric response of engineered domains in ferroelectrics

Rajeev Ahluwalia, Turab Lookman, Avadh Saxena, and Wenwu Cao

Appl. Phys. Lett. 84, 3450 (2004); http://dx.doi.org/10.1063/1.1737059 (3 pages) | Cited 12 times

Online Publication Date: 20 April 2004

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We study the formation of engineered ferroelectric domains in two dimensions based on a continuum approach that incorporates the long-range elastic and electrostatic interactions. The model is also used to simulate the piezoelectric properties of the engineered domain configurations and the response is compared with that of an analogous single domain state. The results show that the low field piezoelectric constants for the engineered configuration are very close to those obtained for the corresponding single domain state and the domain wall influence is not significant. For high fields, domain walls act as nucleation sites for an electric field induced structural transition. © 2004 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
64.60.Q- Nucleation
77.80.Dj Domain structure; hysteresis
77.65.Ly Strain-induced piezoelectric fields
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
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Photoreflectance investigations of oscillator strength and broadening of optical transitions for GaAsSb–GaInAs/GaAs bilayer quantum wells

R. Kudrawiec, G. Sęk, K. Ryczko, J. Misiewicz, and J. C. Harmand

Appl. Phys. Lett. 84, 3453 (2004); http://dx.doi.org/10.1063/1.1737065 (3 pages) | Cited 20 times

Online Publication Date: 20 April 2004

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GaAsSb–GaInAs/GaAs bilayer quantum wells which consist of two adjacent layers of GaAsSb and GaInAs sandwiched between GaAs barriers have been investigated by photoreflectance (PR) spectroscopy. The oscillator strengths of optical transitions in such multiheterointerface structures have been determined from the experiment and compared with the results of envelope function calculations. Additionally, the broadening of the PR features has been analyzed and a correlation has been found with the character of the transitions: the broadening increases significantly when the type of the transition changes from direct to indirect. © 2004 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
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Cyclic surface morphology change related to Li ion movement in Li secondary microbattery embedded in Si substrate: Atomic force microscopy studies

K. Kushida and K. Kuriyama

Appl. Phys. Lett. 84, 3456 (2004); http://dx.doi.org/10.1063/1.1737070 (3 pages) | Cited 6 times

Online Publication Date: 20 April 2004

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Surface morphology and charge/discharge characteristic in a 5×5 μm2 area of an all-solid-state Li secondary battery (Al/Li/SiO2–15 at. %P2O5/LiMn2O4/polycrystalline silicon) embedded in a Si substrate are simultaneously observed by atomic force microscopy with a conductive probe. The battery area of 5×5 μm2 shows charge/discharge behavior corresponding to the movement of ∼ 2.9×1010 Li+ ions/μm2, reflecting the cyclic movement of Li+ ions. The Al electrode consisting of scale-shaped grains of 0.1–1.5 μm in size rises by ∼ 30 nm during the first charge operation. The surface of the Al electrode shows a cyclic change from scaly to wrinkled structures with the charge/discharge operations, indicating the drawing of the excess Li in the anode into the glassy electrolyte. These results are promising for the realization of a micrometer-sized battery. © 2004 American Institute of Physics.
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82.47.Aa Lithium-ion batteries
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Luminescence from processible quantum dot-polymer light emitters 1100–1600 nm: Tailoring spectral width and shape

L. Bakueva, G. Konstantatos, L. Levina, S. Musikhin, and E. H. Sargent

Appl. Phys. Lett. 84, 3459 (2004); http://dx.doi.org/10.1063/1.1737072 (3 pages) | Cited 18 times

Online Publication Date: 20 April 2004

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Electroluminescent devices combining two families of PbS colloidal quantum dots to achieve spectrally tailored two-color emission are reported. Depending on device structure selected—the use of two separated layers versus a mixture of nanocrystals—the structures demonstrated light emission either in two infrared frequency peaks corresponding to the spectral region 1.1–1.6 μm or in a wide band spanning this same spectral region. Separated-layer devices exhibit wide tunability in the relative intensity of the two peaks by varying excitation conditions. Replacing oleate with octodecylamine ligands increases the internal electroluminescence efficiency to 3.1%. © 2004 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.Bc Nanocrystalline materials
81.07.Ta Quantum dots
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.30.Jw Organic compounds, polymers
78.55.Kz Solid organic materials
78.67.Hc Quantum dots

Electronic structure of ZnO nanorods studied by angle-dependent x-ray absorption spectroscopy and scanning photoelectron microscopy

J. W. Chiou, J. C. Jan, H. M. Tsai, C. W. Bao, W. F. Pong, M.-H. Tsai, I.-H. Hong, R. Klauser, J. F. Lee, J. J. Wu, and S. C. Liu

Appl. Phys. Lett. 84, 3462 (2004); http://dx.doi.org/10.1063/1.1737075 (3 pages) | Cited 29 times

Online Publication Date: 20 April 2004

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Angle-dependent x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy measurements were performed to differentiate local electronic structures at the tips and sidewalls of highly aligned ZnO nanorods. The overall intensity of the O K-edge XANES spectra is greatly enhanced for small photon incident angles. In contrast, the overall intensity of the Zn K-edge XANES is much less sensitive to the photon incident angle. Both valence-band photoemission and O K-edge XANES spectra show substantial enhancement of O 2p derived states near the valence band maximum and conduction band minimum, respectively. The spatially resolved Zn 3d core level spectra from tip and sidewall regions show the lack of chemical shift. All the results consistently suggest that the tip surfaces of the highly aligned ZnO nanorods are terminated by O ions and the nanorods are oriented in the [000math] direction. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
76.60.Cq Chemical and Knight shifts
61.46.-w Structure of nanoscale materials
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Coherent terahertz emission from ferromagnetic films excited by femtosecond laser pulses

E. Beaurepaire, G. M. Turner, S. M. Harrel, M. C. Beard, J.-Y. Bigot, and C. A. Schmuttenmaer

Appl. Phys. Lett. 84, 3465 (2004); http://dx.doi.org/10.1063/1.1737467 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2004

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It is shown that the laser induced ultrafast demagnetization of ferromagnetic films results in the emission of a terahertz electromagnetic pulse. This emission has been detected from Ni films using free-space electro-optic sampling. The radiated electric field E(t) is explained by Maxwell equations (radiation from a time dependent magnetic dipole), and is expected to be proportional to the second time derivative of the magnetization d2M/dt2, as measured in the far field. This technique opens appealing perspectives in the context of measuring and understanding the ultrafast spin dynamics as well as the interaction of electrons (both charge and spin) with electromagnetic fields. © 2004 American Institute of Physics.
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75.30.Ds Spin waves
75.60.Jk Magnetization reversal mechanisms
75.30.Wx Spin crossover
75.50.Cc Other ferromagnetic metals and alloys
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
78.20.Jq Electro-optical effects
75.70.Ak Magnetic properties of monolayers and thin films

Engineering molecular rings for magnetocaloric effect

M. Affronte, A. Ghirri, S. Carretta, G. Amoretti, S. Piligkos, G. A. Timco, and R. E. P. Winpenny

Appl. Phys. Lett. 84, 3468 (2004); http://dx.doi.org/10.1063/1.1737468 (3 pages) | Cited 42 times

Online Publication Date: 20 April 2004

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By substituting one Cr3+(s = 3/2) with Cd2+(s = 0) in molecular octanuclear rings, a diluted ensemble of identical nanomagnets with a S = 3/2 ground state, weakly split in zero field, is obtained. The lattice contribution and the essential parameters of the spin Hamiltonian of these uncompensated antiferromagnetic cyclic spin systems are determined by fitting specific heat data between 0.4 and 20 K in magnetic fields up to 7 T. Different entropy contributions are evaluated and results suggest a possible way of engineering molecular magnets to exploit low temperature magnetocaloric effect. © 2004 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
65.40.G- Other thermodynamical quantities
75.50.Xx Molecular magnets
61.46.-w Structure of nanoscale materials
75.10.Dg Crystal-field theory and spin Hamiltonians
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Raman line shape of the A1 longitudinal optical phonon in GaN

L. Shi, F. A. Ponce, and J. Menéndez

Appl. Phys. Lett. 84, 3471 (2004); http://dx.doi.org/10.1063/1.1737792 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2004

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High-resolution Raman measurements of the A1 longitudinal optical (LO) phonon in GaN reveal a complex line shape that can be explained in terms of the angular dispersion of LO phonons in this material. A simple geometrical model of the line shape makes it possible to extract the true anharmonic full width at half maximum 2Γ of the A1(LO) mode. The value of this parameter, 2Γ=2.4 cm−1 at 20 K, is in much better agreement with time-domain measurements by Tsen and co-workers [Appl. Phys. Lett. 72, 2132 (1998)] than any previous frequency-domain measurement. The results indicate that angular dispersion effects must be carefully considered in any analysis of Raman spectra from noncubic crystals. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
63.20.Ry Anharmonic lattice modes
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p-type behavior in phosphorus-doped (Zn,Mg)O device structures

Y. W. Heo, Y. W. Kwon, Y. Li, S. J. Pearton, and D. P. Norton

Appl. Phys. Lett. 84, 3474 (2004); http://dx.doi.org/10.1063/1.1737795 (3 pages) | Cited 115 times

Online Publication Date: 20 April 2004

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The characteristics of device structures that employ phosphorus-doped (Zn,Mg)O have been examined in a effort to delineate the carrier type behavior in this material. The capacitance–voltage properties of metal/insulator/P-doped (Zn,Mg)O diode structures were measured and found to exhibit a polarity consistent with the P-doped (Zn,Mg)O layer being p type. In addition, thin-film junctions comprising n-type ZnO and P-doped (Zn,Mg)O display asymmetric I–V characteristics that are consistent with the formation of a p–n junction at the interface. Although Hall measurements of the P-doped (Zn,Mg)O thin films yielded an indeterminate Hall sign due to a small carrier mobility, these results are consistent with previous reports that phosphorus can yield an acceptor state and p-type behavior in ZnO materials. © 2004 American Institute of Physics.
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85.30.Kk Junction diodes
61.72.uj III-V and II-VI semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
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Local built-in potential on grain boundary of Cu(In,Ga)Se2 thin films

C.-S. Jiang, R. Noufi, J. A. AbuShama, K. Ramanathan, H. R. Moutinho, J. Pankow, and M. M. Al-Jassim

Appl. Phys. Lett. 84, 3477 (2004); http://dx.doi.org/10.1063/1.1737796 (3 pages) | Cited 48 times

Online Publication Date: 20 April 2004

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We report on a direct measurement of two-dimensional potential distribution on the surface of photovoltaic Cu(In,Ga)Se2 thin films using a nanoscale electrical characterization of scanning Kelvin probe microscopy. The potential measurement reveals a higher surface potential or a smaller work function on grain boundaries of the film than on the grain surfaces. This demonstrates the existence of a local built-in potential on grain boundaries, and the grain boundary is positively charged. The local built-in potential on the grain boundary is expected to increase the minority-carrier collection area from one to three dimensional. In addition, a work function decrease induced by Na on the film surface was observed. © 2004 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Pz Photoconduction and photovoltaic effects
61.72.Mm Grain and twin boundaries
68.37.Ps Atomic force microscopy (AFM)
72.80.Jc Other crystalline inorganic semiconductors
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Self-assembled hexagonal Au particle networks on silicon from Au nanoparticle solution

P. Y. Su, J. C. Hu, S. L. Cheng, L. J. Chen, and J. M. Liang

Appl. Phys. Lett. 84, 3480 (2004); http://dx.doi.org/10.1063/1.1737797 (3 pages) | Cited 16 times

Online Publication Date: 20 April 2004

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Self-assembled hexagonal Au particle networks, 2–12 μm in cell size, on silicon have been achieved by a simple method. Honeycomb structure of Au nanoparticles on silicon was drop cast from the Au nanoparticle solution under appropriate concentration, evaporation rate, substrate temperature, and humidity. Hexagonal networks with discrete Au particles were generated in samples annealed in N2 ambient. Two-step annealing, i.e., annealing at 400 °C followed by annealing at 1000 °C for 1 h each was found to be effective to improve the regularity of the Au particle network. As the cell size can be adjusted by the tuning of the deposition conditions, the scheme promises to be an effective patterning method without complex lithography. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
82.70.Dd Colloids
68.47.Fg Semiconductor surfaces
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High doping incorporation on (311)B InP/InGaAs by metalorganic chemical vapor deposition and its application to tunnel junction fabrication

Yae L. Okuno, Steven P. DenBaars, and John E. Bowers

Appl. Phys. Lett. 84, 3483 (2004); http://dx.doi.org/10.1063/1.1737798 (3 pages) | Cited 1 time

Online Publication Date: 20 April 2004

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We investigated the doping characteristics of InP/InGaAs on the (311)B plane by metalorganic chemical vapor deposition using metalorganic group-V regents. For both n-type Si doping and p-type Zn doping, we found that dopant incorporation is higher on the (311)B plane than the (100) plane. Applying this result, we grew a tunnel junction on (311)B InP substrates at a constant growth temperature. The junction showed good current–voltage characteristics and is promising for device applications. © 2004 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.S- Impurities in crystals
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Blueshift of yellow luminescence band in self-ion-implanted n-GaN nanowire

S. Dhara, A. Datta, C. T. Wu, Z. H. Lan, K. H. Chen, Y. L. Wang, Y. F. Chen, C. W. Hsu, L. C. Chen, H. M. Lin, and C. C. Chen

Appl. Phys. Lett. 84, 3486 (2004); http://dx.doi.org/10.1063/1.1738172 (3 pages) | Cited 18 times

Online Publication Date: 20 April 2004

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Optical photoluminescence studies are performed in self-ion (Ga+)-implanted nominally doped n-GaN nanowires. A 50 keV Ga+ focused ion beam in the fluence range of 1×1014–2×1016 ions cm−2 is used for the irradiation process. A blueshift is observed for the yellow luminescence (YL) band with increasing fluence. Donor–acceptor pair model with emission involving shallow donor introduced by point-defect clusters related to nitrogen vacancies and probable deep acceptor created by gallium interstitial clusters is responsible for the shift. High-temperature annealing in nitrogen ambient restores the peak position of YL band by removing nitrogen vacancies. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.La Quantum wires (patterned in quantum wells)
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters
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Double-well model of dielectric relaxation current

John R. Jameson, Walter Harrison, P. B. Griffin, and J. D. Plummer

Appl. Phys. Lett. 84, 3489 (2004); http://dx.doi.org/10.1063/1.1738177 (3 pages) | Cited 15 times

Online Publication Date: 20 April 2004

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We show that a straightforward account of dielectric relaxation current in glasses follows from a semiclassical treatment of the double-well model [P. W. Anderson, B. I. Halperin, and C. M. Varma, Philos. Mag. 25, 1 (1972) and W. A. Phillips, J. Low Temp. Phys. 7, 351 (1972)] explaining the linear specific heat of glasses at low temperature. The current is obtained from the field-induced tunneling of the glass between the minima of its potential energy surface, and is found to have the experimentally observed linear dependence on field and inverse dependence on time. The effects of temperature and prior biases are briefly discussed, as well as the relation of the model to the theory of charge trapping. No dielectric relaxation is expected in a perfect insulating crystal, raising the important technological question of how perfect high-k dielectrics like HfO2 and ZrO2 must be in order to serve as gate dielectrics in transistors.© 2004 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
65.40.Ba Heat capacity
77.22.Ch Permittivity (dielectric function)
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Model for the photoinduced formation of diffraction gratings in liquid-crystalline composite materials

A. Veltri, R. Caputo, C. Umeton, and A. V. Sukhov

Appl. Phys. Lett. 84, 3492 (2004); http://dx.doi.org/10.1063/1.1738182 (3 pages) | Cited 29 times

Online Publication Date: 20 April 2004

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We modelize the photoinduced formation of switchable diffraction gratings in polymer-based liquid-crystalline composite materials. The model assumes that redistribution of molecules is due to mass diffusion and incorporates a realistic kinetic description of polymerization processes. Numerical simulations predict two different kinds of structure that have already been experimentally observed. Two parameters governing the phenomenon are pointed out, which determine the structure that will be formed after the curing process has been completed. © 2004 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.79.Dj Gratings
42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
82.35.-x Polymers: properties; reactions; polymerization
61.41.+e Polymers, elastomers, and plastics
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Very high spin polarization in GaAs by injection from a (Ga,Mn)As Zener diode

P. Van Dorpe, Z. Liu, W. Van Roy, V. F. Motsnyi, M. Sawicki, G. Borghs, and J. De Boeck

Appl. Phys. Lett. 84, 3495 (2004); http://dx.doi.org/10.1063/1.1738515 (3 pages) | Cited 63 times

Online Publication Date: 20 April 2004

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We demonstrate an electrically injected electron spin polarization in GaAs of 80% at 4.6 K by interband tunneling from the valence band of (Ga,Mn)As into an (Al,Ga)As light-emitting diode. The polarization is analyzed by the oblique Hanle effect and vanishes at 120 K, the Curie temperature of the (Ga,Mn)As injector. The temperature and the bias dependence of the polarization are explained in terms of the properties of the (Ga,Mn)As/GaAs diode. © 2004 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.60.Jb Light-emitting devices
73.20.At Surface states, band structure, electron density of states

Suppressing of optical quenching of deep defect-to-band transitions in AlGaN and GaN/AlGaN heterostructures

H. Witte, E. Schrenk, K. Flügge, A. Krtschil, M. Lisker, A. Krost, J. Christen, B. Kuhn, and F. Scholz

Appl. Phys. Lett. 84, 3498 (2004); http://dx.doi.org/10.1063/1.1738517 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2004

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Quenching of photocurrent spectroscopy and thermally stimulated currents has been investigated in undoped AlGaN layers and GaN/AlGaN heterostructures grown by metalorganic vapor phase epitaxy on sapphire substrates. The quenching was induced by an additional illumination as well as by an excitation with light below bandgap energy, respectively. In GaN layers, mainly the thermal defect emission band between 210 and 300 K is involved in the quenching processes and there are strong indications of a reduction of the band by incorporation of aluminum. In AlGaN layers, a decrease of quenching with increasing Al content is observed in accordance to a reduction of the height of the thermal emission between 210 and 300 K in these layers. These results are supported by quenching experiments in AlGaN/GaN heterostructures. © 2004 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.55.Eq III-V semiconductors
79.60.Jv Interfaces; heterostructures; nanostructures
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Near-bandedge cathodoluminescence of an AlN homoepitaxial film

E. Silveira, J. A. Freitas, M. Kneissl, D. W. Treat, N. M. Johnson, G. A. Slack, and L. J. Schowalter

Appl. Phys. Lett. 84, 3501 (2004); http://dx.doi.org/10.1063/1.1738929 (3 pages) | Cited 30 times

Online Publication Date: 20 April 2004

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Cathodoluminescence experiments were performed on a high-quality AlN epitaxial film grown by organometallic vapor phase epitaxy on a large single crystal AlN substrate. The low-temperature near-bandedge spectra clearly show six very narrow lines. The thermal quenching behavior of these emission lines provides insight on how to assign them to free and bound exciton recombination processes. The binding energy for the free-exciton-A in AlN was found to be nearly twice that in GaN. The observation of the free-exciton-A first excited state permitted us to estimate its reduced effective mass and, by using recent reported values for the hole effective mass in Mg-doped AlN, the electron effective mass in AlN has been deduced. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.35.-y Excitons and related phenomena
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology

Wafer-bonded semiconductors using In/Sn and Cu/Ti metallic interlayers

Frank Shi, Hao Chen, and Scott MacLaren

Appl. Phys. Lett. 84, 3504 (2004); http://dx.doi.org/10.1063/1.1738933 (3 pages) | Cited 5 times

Online Publication Date: 20 April 2004

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This work reports on the interface microstructures and interface electrical and optical properties of wafer-bonded semiconductors using In/Sn and Cu/Ti as the metallic interlayers. The interface microstructures of the wafer-bonded semiconductors were characterized using transmission electron microscopy and scanning electron microscopy. The interface imperfections and their potential influences on the interface electrical performances were discussed. The interface electrical and optical characteristics of the metal-bonded wafers were also compared with those of directly fused wafers. © 2004 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
68.35.Ct Interface structure and roughness
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.37.Lp Transmission electron microscopy (TEM)
78.66.Fd III-V semiconductors
78.66.Db Elemental semiconductors and insulators
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
73.40.Ns Metal-nonmetal contacts
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Direct printing of nanoparticles and spin-on-glasses by offset liquid embossing

Eric J. Wilhelm and Joseph M. Jacobson

Appl. Phys. Lett. 84, 3507 (2004); http://dx.doi.org/10.1063/1.1738942 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2004

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We describe offset liquid embossing (OLE), a method for additively printing nanoparticles and spin-on-glasses. OLE utilizes the transfer of patterned material from a polydimethylsiloxane surface of tuned wettability to a rigid or flexible substrate. Multiple layers can be aligned and printed without the need for planarization. The printing is fast (10 s transfer to substrate) and can be done at ambient conditions. Bridge-like structures were printed in spin-on-glass without etching. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.65.-b Surface treatments
68.08.Bc Wetting
81.07.Bc Nanocrystalline materials
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