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28 Aug 2006

Volume 89, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 093101 (2006); http://dx.doi.org/10.1063/1.2338808 (3 pages)

Nicholas Jabari Lee, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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Organic-inorganic hybrid dielectrics with low leakage current for organic thin-film transistors

Sunho Jeong, Dongjo Kim, Sul Lee, Bong-Kyun Park, and Jooho Moon

Appl. Phys. Lett. 89, 092101 (2006); http://dx.doi.org/10.1063/1.2338753 (3 pages) | Cited 21 times

Online Publication Date: 28 August 2006

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Using a thermally cross-linkable organosiloxane-based organic-inorganic hybrid material, a solution-processable gate dielectric layer for organic thin-film transistors has been fabricated. The hybrid dielectric was synthesized by a sol-gel process, followed by heat treatment at below 190 °C. Dielectric strength of 1.4–1.65 MV/cm was measured and it was confirmed that the leakage current is governed by the Poole-Frenkel emission mechanism in which the silanol groups act as trap sites. An organic thin-film transistor utilizing the hybrid dielectric shows similar electrical performance to a transistor fabricated using surface-modified thermally grown SiO2.
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85.30.Tv Field effect devices
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Junction characteristics of SrTiO3 or BaTiO3 on p-Si (100) heterostructures

D. Hunter, K. Lord, T. M. Williams, K. Zhang, A. K. Pradhan, D. R. Sahu, and J.-L. Huang

Appl. Phys. Lett. 89, 092102 (2006); http://dx.doi.org/10.1063/1.2338764 (3 pages) | Cited 12 times

Online Publication Date: 28 August 2006

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The authors report the fabrication of p-n junctions, consisting of n-type SrTiO3 or BaTiO3 and p-type Si substrates, by the pulsed-laser deposition technique. The BaTiO3/Si junction exhibits excellent rectifying behavior and significantly reduced leakage current at 300 K exceeding breakdown voltage of −25 V with leakage current <0.5 μA, while SrTiO3/Si with an interfacial layer shows moderate junction characteristics. It was demonstrated that the BaTiO3/Si grown at an optimum growth temperature of 650 °C displayed superior performance which is promising for electronic devices. Both junctions show photocurrent at 300 K due to electron injection following the photoexcitation of n-type perovskite.
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73.40.Ei Rectification
72.40.+w Photoconduction and photovoltaic effects
77.22.Jp Dielectric breakdown and space-charge effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Electron energy barriers at interfaces of GaAs(100) with LaAlO3 and Gd2O3

V. V. Afanas’ev, A. Stesmans, R. Droopad, M. Passlack, L. F. Edge, and D. G. Schlom

Appl. Phys. Lett. 89, 092103 (2006); http://dx.doi.org/10.1063/1.2338893 (3 pages) | Cited 9 times

Online Publication Date: 28 August 2006

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Electron energy barriers at the interfaces of GaAs(100) with Gd2O3 appear to be insensitive to the Fermi level pinning indicating that charges at interface states are of marginal importance for the band alignment at semiconductor/insulator interfaces. The inferred conduction band offset of 1.6±0.1 eV for GaAs(100)/Gd2O3 is close to that measured at the GaAs(100)/LaAlO3 interface which is consistent with the 5.8 and 5.7 eV wide band gaps of these two insulators. However, the defects revealed by photoionization measurements exhibit a distinctly different in-depth distribution. In GaAs/LaAlO3 most of the traps are located close to the semiconductor surface, while in GaAs/Gd2O3 case they are found distributed across the entire oxide layer.
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73.20.At Surface states, band structure, electron density of states
68.47.Fg Semiconductor surfaces
71.55.Eq III-V semiconductors

Low-temperature silicon wafer bonding based on Ti/Si solid-state amorphization

Jian Yu, Yinmin Wang, Jian-Qiang Lu, and Ronald J. Gutmann

Appl. Phys. Lett. 89, 092104 (2006); http://dx.doi.org/10.1063/1.2338574 (3 pages) | Cited 3 times

Online Publication Date: 28 August 2006

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Strong and nearly void-free bonding has been achieved using a low-temperature Ti/Si-based wafer bonding technique. Bare Si wafers are bonded with oxidized Si wafers at temperatures from 300 to 450 °C, using ∼ 30 nm thick Ti as bonding intermediate. High-resolution transmission electron microscopy and electron energy-loss spectrometry elemental mapping indicate that the strong bonding is attributed to a solid-state amorphization between Ti and Si. Ti demonstrates particularly attractive capabilities to overcome kinetic barriers commonly associated with low-temperature silicon wafer bonding.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.-z Semiconductor devices

Ballistic transport in induced one-dimensional hole systems

O. Klochan, W. R. Clarke, R. Danneau, A. P. Micolich, L. H. Ho, A. R. Hamilton, K. Muraki, and Y. Hirayama

Appl. Phys. Lett. 89, 092105 (2006); http://dx.doi.org/10.1063/1.2337525 (3 pages) | Cited 26 times

Online Publication Date: 29 August 2006

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The authors have fabricated and studied a ballistic one-dimensional p-type quantum wire using an undoped AlGaAs/GaAs heterostructure. The absence of modulation doping eliminates remote ionized impurity scattering and allows high mobilities to be achieved over a wide range of hole densities and, in particular, at very low densities where carrier-carrier interactions are strongest. The device exhibits clear quantized conductance plateaus with highly stable gate characteristics. These devices provide opportunities for studying spin-orbit coupling and interaction effects in mesoscopic hole systems in the strong interaction regime where rs>10.
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73.23.Ad Ballistic transport
73.63.Nm Quantum wires
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.Fr Low-field transport and mobility; piezoresistance
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Sharp-line electroluminescence from individual quantum dots by resonant tunneling injection of carriers

L. Turyanska, A. Baumgartner, A. Chaggar, A. Patanè, L. Eaves, and M. Henini

Appl. Phys. Lett. 89, 092106 (2006); http://dx.doi.org/10.1063/1.2337540 (3 pages) | Cited 2 times

Online Publication Date: 29 August 2006

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We report sharp electroluminescence lines from individual self-assembled InAs quantum dots (QDs) excited by resonant tunneling injection of carriers from the n- and p-doped GaAs layers of a p-i-n diode. Bias-tunable tunneling of carriers into the dots provides a means of controlling injection and light emission from a small number of individual dots within a large ensemble. We also show that the extent of carrier energy relaxation prior to recombination can be controlled by tailoring the morphology of the QD layer.
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78.67.Hc Quantum dots
78.60.Fi Electroluminescence
73.63.Kv Quantum dots
73.40.Gk Tunneling
85.60.Dw Photodiodes; phototransistors; photoresistors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photoluminescence studies of impurity transitions in AlGaN alloys

N. Nepal, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 89, 092107 (2006); http://dx.doi.org/10.1063/1.2337856 (3 pages) | Cited 25 times

Online Publication Date: 29 August 2006

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Deep ultraviolet photoluminescence (PL) spectroscopy has been employed to investigate impurity transitions in Si doped Al-rich AlGaN alloys. In addition to the previously reported donor compensating centers—isolated cation vacancy with three negative charges (VIII)3− and cation vacancy complex with two-negative charges (VIII complex)2−—a group of impurity transitions with higher emission energies has been observed in AlGaN alloys grown under different conditions, which has been assigned to the recombination between shallow donors and cation vacancy complexes with one-negative charge (VIII complex)−1. Similar to (VIII)3− and (VIII complex)2−, the energy levels of (VIII complex)1− deep acceptors in AlxGa1−xN (0 ⩽ x ⩽ 1) alloys are pinned to a common energy level in vacuum. A strong correlation between the resistivity and PL emission intensities of the impurity transitions associated with cation vacancies (and complexes) was found.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

LnPdSb (Ln = La,Gd): Promising intermetallics with large carrier mobility for high performance p-type thermoelectric materials

Takeyuki Sekimoto, Ken Kurosaki, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 89, 092108 (2006); http://dx.doi.org/10.1063/1.2339886 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2006

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The authors studied the thermoelectric properties of LaPdSb and GdPdSb. The values of the thermoelectric power were positive and relatively large (60–100 μV/K). The values of the electrical resistivity were on the order of 10−4 Ω cm, which is unexpectedly low in view of the large values observed for the thermoelectric power. From the Hall effect measurements, the unusually low electrical resistivity was confirmed to be caused by the large carrier mobility. LaPdSb indicated a large power factor of 50 μW/K2 cm at 327 K and a large dimensionless figure of merit of 0.26 at around room temperature.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Optical properties of GaN and GaMnN nanowires grown on sapphire substrates

Eunsoon Oh, Jung Ho Choi, Han-Kyu Seong, and Heon-Jin Choi

Appl. Phys. Lett. 89, 092109 (2006); http://dx.doi.org/10.1063/1.2243868 (3 pages) | Cited 10 times

Online Publication Date: 29 August 2006

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The authors discussed the photoluminescence (PL) spectra of GaN and GaMnN nanowires grown on sapphire substrates. Comparison of the excitonic PL peak energy with bulk GaN indicates that the strain of the nanowires is fully relaxed. For GaMnN nanowires, the redshift of the PL peak with increasing temperature was larger than that of the GaN nanowires, which was explained by redistribution of carriers into localization sites. The absence of Zeeman shift and circular polarization in GaMnN nanowires indicates that the exchange interaction between carriers and Mn2+ has to be at least one order of magnitude smaller than that in Cd0.94Mn0.06S nanowires.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
75.50.Pp Magnetic semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

Wavelength-selective organic field-effect phototransistors based on dye-doped poly-3-hexylthiophene

R. M. Meixner, H. Göbel, F. A. Yildirim, W. Bauhofer, and W. Krautschneider

Appl. Phys. Lett. 89, 092110 (2006); http://dx.doi.org/10.1063/1.2344838 (3 pages) | Cited 11 times

Online Publication Date: 29 August 2006

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The authors present a strategy to manufacture wavelength-selective field-effect phototransistors by employing dye-doped poly-3-hexylthiophene (P3HT) as a semiconducting layer. The dye doping of the semiconductor P3HT was achieved by blending organic molecules—coumarin 6, oxazine 1, and nile red—into the conjugated organic polymer. Illuminating these transistors with monochromatic light in the range of 400–700 nm resulted in varying conductivities for certain wavelengths in dependence on the particular dye. This effect is attributed to the photogeneration of excitons on the dye molecules, which are subsequently transferred to the conjugated polymer.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Tv Field effect devices

Chemical synthesis and magnetic properties of dilute magnetic ZnTe:Cr crystals

Lijuan Zhao, Bei Zhang, Qi Pang, Shihe Yang, Xixiang Zhang, Weikun Ge, and Jiannong Wang

Appl. Phys. Lett. 89, 092111 (2006); http://dx.doi.org/10.1063/1.2337561 (3 pages) | Cited 5 times

Online Publication Date: 30 August 2006

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ZnTe and Cr doped ZnTe crystals have been synthesized using a solvothermal process. The characterizations by x-ray diffraction and transmission electron microscopy show that the synthesized ZnTe:Cr crystals have a cubic structure and Cr is incorporated into ZnTe. The magnetic properties of ZnTe:Cr are investigated. A hysteresis is observed in the magnetization versus magnetic field measurements below 10 K. The detailed analyses suggest that the hysteresis possibly originated from the magnetic short-range ordering of Zn1−xCrxTe compounds in the sample.
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75.50.Pp Magnetic semiconductors
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
81.10.Dn Growth from solutions
68.37.Lp Transmission electron microscopy (TEM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Electronic and magnetic properties of the Ag-doped Fe3O4 films studied by x-ray absorption spectroscopy

S. H. Liu, H. M. Tsai, C. W. Pao, J. W. Chiou, D. C. Ling, W. F. Pong, M.-H. Tsai, H. J. Lin, L. Y. Jang, J. F. Lee, J. H. Hsu, W. J. Wang, and C. J. Hsu

Appl. Phys. Lett. 89, 092112 (2006); http://dx.doi.org/10.1063/1.2338889 (3 pages) | Cited 4 times

Online Publication Date: 30 August 2006

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The electronic and magnetic properties of Ag-doped Fe3O4 films were studied by x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS), and x-ray magnetic circular dichroism (XMCD) measurements. A comparison between the Ag K-edge EXAFS Fourier transform spectra of Ag-doped Fe3O4 and the Ag metal shows that Ag atoms aggregate into Ag granules. The O K-edge and Ag L3-edge XANES spectra consistently indicate an electron transfer from the Fe3O4 host into Ag granules. The Fe L3,2-edge XMCD spectra and hysteresis measurements reveal that Ag granules reduce the average magnetic moment of Fe ions and the saturation magnetization of Fe3O4.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.20.Ps Other inorganic compounds

Large fluorine-vacancy clusters in Si and their capture efficiency for self-interstitials

Giorgia M. Lopez and Vincenzo Fiorentini

Appl. Phys. Lett. 89, 092113 (2006); http://dx.doi.org/10.1063/1.2338555 (3 pages) | Cited 10 times

Online Publication Date: 30 August 2006

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Based on ab initio density-functional energetics for saturated (n = 2m+2) fluorine-vacancy clusters FnVm for m up to 4, the authors set up a model showing that (a) fluorine-vacancy (F–V) aggregates in Si can form in any size and concentration for sufficient concentrations of incorporated (e.g., implanted) F, and (b) the F to V ratio in F–V complexes (i.e., the inverse capture efficiency of self-interstitials) is an ensemble average over many cluster sizes. It ranges between 4 and 2, with typical values of 2.2–2.5, consistent with recent experimental estimates.
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61.72.J- Point defects and defect clusters

Effects of grain size on the mosaic tilt and twist in InN films grown on GaN by metal-organic chemical vapor deposition

H. Wang, Y. Huang, Q. Sun, J. Chen, L. L. Wang, J. J. Zhu, D. G. Zhao, S. M. Zhang, D. S. Jiang, Y. T. Wang, and H. Yang

Appl. Phys. Lett. 89, 092114 (2006); http://dx.doi.org/10.1063/1.2345224 (3 pages) | Cited 6 times

Online Publication Date: 30 August 2006

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The structural property of InN films grown on Ga-face GaN layers by metal-organic chemical vapor deposition has been studied by high-resolution x-ray diffraction. The mosaic tilt and twist are found to be strongly dependent on the surface lateral grain size. The twist decreases with increasing grain size and finally approaches to a constant level. On the other hand, the mosaic tilt increases substantially when the grain size becomes large enough and exceeds the width of step terraces on the GaN surface, showing an important mechanism for the defect generation in the InN/GaN system with large out-of-plane lattice mismatch.
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68.55.-a Thin film structure and morphology

Tailoring electronic and charge transport properties of molecular π-stacked heterojunctions

Alain Rochefort and Paul Boyer

Appl. Phys. Lett. 89, 092115 (2006); http://dx.doi.org/10.1063/1.2266228 (3 pages) | Cited 3 times

Online Publication Date: 31 August 2006

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The electronic structure and charge transport properties of π-stacked heterojunctions formed by two different 3,6-R2-1-ethylnaphthalene (R: H, CH3, Cl) fragments have been investigated with a tight binding method. The extent of the evanescent wave function that escapes across the interface near EF is shorter when chloride groups are used to modify the π-electron distribution of the naphthalene core than when methyl groups are used. Consequently, the tunneling of carriers in CH3-heterojunction is significantly larger than for systems containing chloride groups. This shows that specific electronic properties can be tailored on naphthalene-based assemblies in which a judicious combination of functional groups is considered.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling

Two-subband-populated AlGaN/GaN heterostructures probed by electrically detected and microwave-modulated magnetotransport measurements

D. R. Hang, C. F. Huang, and Y. F. Chen

Appl. Phys. Lett. 89, 092116 (2006); http://dx.doi.org/10.1063/1.2339030 (3 pages) | Cited 6 times

Online Publication Date: 31 August 2006

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The authors apply the microwave-modulated technique to study the transport properties of two-subband-populated AlGaN/GaN heterostructures. The microwave modulation enhances the small Shubnikov–de Haas oscillations at low magnetic fields, providing a direct way to compare the mobilities of different subbands from the experimental data. In addition, this technique can help us to determine the subband-energy separation, especially when the population of the second subband is much lower than that of the first one. Variation of subband-energy separation due to different spacer thicknesses is obtained. Therefore, the authors showed a powerful way to probe parameters of two-subband-populated AlGaN/GaN heterostructures.
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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

Epitaxial growth of Sc2O3 films on GaN

A. M. Herrero, B. P. Gila, C. R. Abernathy, S. J. Pearton, V. Craciun, K. Siebein, and F. Ren

Appl. Phys. Lett. 89, 092117 (2006); http://dx.doi.org/10.1063/1.2270058 (3 pages) | Cited 13 times

Online Publication Date: 31 August 2006

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Thin films of scandium oxide were epitaxially deposited on GaN via molecular beam epitaxy using elemental Sc and an oxygen plasma. After growth, the Sc2O3 films were annealed at a temperature of 800 °C for 5 min in the growth chamber. The structural quality of Sc2O3 films, before and after annealing, was characterized using high-resolution x-ray diffraction, atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM). AFM of the films revealed smooth surfaces with 0.38 nm root mean square roughness and show evidence of step-flow growth. The rocking curve and reflectivity scans of the films reveal that the Sc2O3/GaN interface is abrupt and that it remains so after annealing. Pole figure and grazing incidence θ-2θ measurements show that the films are very textured along the c axis of the GaN substrate. HRTEM produced lattice images of the Sc2O3/GaN interface illustrating the single crystal growth of the Sc2O3 films on the GaN.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing

Heating and cooling in semiconductor structures by an electric current

G. N. Logvinov, J. E. Velázquez, I. M. Lashkevych, and Yu. G. Gurevich

Appl. Phys. Lett. 89, 092118 (2006); http://dx.doi.org/10.1063/1.2345033 (3 pages) | Cited 7 times

Online Publication Date: 31 August 2006

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A comprehensive study of the mechanisms of heating and cooling originated by an electrical current in semiconductor devices is reported. The authors studied the Peltier, Joule, and Thomson phenomena self-consistently and found that the magnitudes of all of them were commensurable. A new formulation and interpretation of the Thomson effect are offered. The main conclusion of the present work is that the thermal analysis of any semiconductor device under real working conditions demands the inclusion of all heating and cooling mechanisms simultaneously.
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07.20.Hy Furnaces; heaters
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Effect of growth conditions on the magnetic characteristics of GaGdN

J. K. Hite, R. M. Frazier, R. Davies, G. T. Thaler, C. R. Abernathy, S. J. Pearton, and J. M. Zavada

Appl. Phys. Lett. 89, 092119 (2006); http://dx.doi.org/10.1063/1.2337082 (3 pages) | Cited 13 times

Online Publication Date: 31 August 2006

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GaGdN layers were grown by gas source molecular beam epitaxy with varying crystal quality and Gd concentrations as set by the Gd cell temperature. Magnetic measurements showed ferromagnetic behavior at room temperature, with the saturation magnetization dependent both on Gd concentration and crystalline quality. The Gd concentration was under the detection limit of secondary ion mass spectrometry, and estimated to be on the order of <1017 at./cm3. As expected at this low dopant concentration, x-ray diffraction measurements showed the films to be single phase. Gd-doped samples codoped with Si to make them conducting with resistivity of 0.04 Ω cm showed similar magnetic properties as Gd-doped films without addition of Si.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth
73.61.Ey III-V semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Defect generation at SiO2/Si interfaces by low pressure chemical vapor deposition of silicon nitride

Hao Jin, K. J. Weber, and P. J. Smith

Appl. Phys. Lett. 89, 092120 (2006); http://dx.doi.org/10.1063/1.2345247 (3 pages) | Cited 4 times

Online Publication Date: 1 September 2006

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Low pressure chemical vapor deposition of Si3N4 on oxidized Si (111) surfaces causes a change in the properties of the dominant interface defect, the Pb center, observed by electron paramagnetic resonance. The change in the signature of the Pb center is consistent with the formation of an oxynitride layer at the interface, which could be formed during the initial stages of nitride layer deposition. Photoconductivity decay measurements show a concomitant increase in the minority carrier recombination rate at the Si surface. The modified Si surface shows a worse thermal stability than the as-oxidized Si surface.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.At Surface states, band structure, electron density of states
71.55.Cn Elemental semiconductors
76.30.Mi Color centers and other defects
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Synthesis of YbyCo4Sb12/Yb2O3 composites and their thermoelectric properties

X. Y. Zhao, X. Shi, L. D. Chen, W. Q. Zhang, S. Q. Bai, Y. Z. Pei, X. Y. Li, and T. Goto

Appl. Phys. Lett. 89, 092121 (2006); http://dx.doi.org/10.1063/1.2345249 (3 pages) | Cited 52 times

Online Publication Date: 1 September 2006

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Composites containing Yb-filled CoSb3 and well-distributed Yb2O3 particles are synthesized by in situ reaction method. The structural, chemical, and transport properties of the composites are studied. Some Yb2O3 particles with microsize locate at the grain boundaries of matrix and others distribute within YbyCo4Sb12 grains as nanoscale inclusions. The combination of the “rattling” of Yb ions inside the voids of CoSb3 and the phonon scattering of the oxide defects results in a remarkable reduction in the lattice thermal conductivity. The thermoelectric performance of the composites is significantly improved, and the maximum figures of merit reach 1.3 for the Yb0.25Co4Sb12/Yb2O3 and 1.2 for the Yb0.21Co4Sb12/Yb2O3 composites at 850 K.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
61.72.Mm Grain and twin boundaries
61.72.Qq Microscopic defects (voids, inclusions, etc.)
63.20.-e Phonons in crystal lattices

Deep acceptor states in ZnO single crystals

H. von Wenckstern, R. Pickenhain, H. Schmidt, M. Brandt, G. Biehne, M. Lorenz, M. Grundmann, and G. Brauer

Appl. Phys. Lett. 89, 092122 (2006); http://dx.doi.org/10.1063/1.2335798 (3 pages) | Cited 38 times

Online Publication Date: 1 September 2006

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The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO wafer grown by pressurized melt growth with nitrogen ions. The authors found the commonly observed donorlike defects E1 and E3 and two acceptorlike defects A2 and A3, as well as a broad acceptorlike defect band. The thermal activation energies of A2 and A3, were determined to be about 150 and 280 meV, respectively.
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71.55.Gs II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Accurate dependence of gallium nitride thermal conductivity on dislocation density

C. Mion, J. F. Muth, E. A. Preble, and D. Hanser

Appl. Phys. Lett. 89, 092123 (2006); http://dx.doi.org/10.1063/1.2335972 (3 pages) | Cited 24 times

Online Publication Date: 1 September 2006

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The authors experimentally find that the thermal conductivity of gallium nitride depends critically on dislocation density using the 3-omega technique. For GaN with dislocation densities lower than 106 cm−2, the thermal conductivity is independent with dislocation density. The thermal conductivity decreases with a logarithmic dependence for material with dislocation densities in the range of 107–1010 cm−2. These results are in agreement with theoretical predictions. This study indicates that the hydride vapor phase epitaxy method offers an attractive route for the formation of semi-insulating gallium nitride with optimal thermal conductivity values around 230 W/m K and very low dislocation density near 5×104 cm−2.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Nonlinear electrical properties of three-terminal junctions

D. Wallin, I. Shorubalko, H. Q. Xu, and A. Cappy

Appl. Phys. Lett. 89, 092124 (2006); http://dx.doi.org/10.1063/1.2344849 (3 pages) | Cited 29 times

Online Publication Date: 1 September 2006

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The authors report on room-temperature electrical measurements of three-terminal junctions made from a semiconductor heterostructure. The correlation between the junction size of the devices and the voltages needed to be applied in order to observe the electrical characteristics of three-terminal ballistic junctions is studied. The authors show that the ballistic behavior of electron transport can be observed in a three-terminal junction with a junction size of a few micrometers, much larger than the mean free path of electrons in the material. The results are explained in terms of a bias-induced enhancement of the electron mean free path in the system.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.23.Ad Ballistic transport
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ht High-field and nonlinear effects

Passivation of air-exposed AlGaAs using low frequency plasma-enhanced chemical vapor deposition of silicon nitride

A. Jaouad and V. Aimez

Appl. Phys. Lett. 89, 092125 (2006); http://dx.doi.org/10.1063/1.2345030 (3 pages) | Cited 3 times

Online Publication Date: 1 September 2006

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The authors report on the development of a simple passivation technique of air-exposed AlxGa1−xAs using (NH4)2S treatment and low frequency plasma-enhanced chemical vapor deposition of silicon nitride. Metal-insulator-semiconductor capacitors were fabricated on p-AlxGa1−xAs substrates and characterized using capacitance-voltage and conductance-frequency measurements. Modulation of the surface potential is observed and unpinning of Fermi level is demonstrated. The minimum interface state density as estimated using conductance method is in the order of (2–3)×1012 cm−2 eV−1. The passivation potential of the low frequency plasma may be explained by the high level of hydrogen bombardment of the substrate.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
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