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22 Jan 2007

Volume 90, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 043507 (2007); http://dx.doi.org/10.1063/1.2435508 (3 pages)

D. Y. Kim and A. J. Steckl
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Photogalvanic effects for interband absorption in AlGaN/GaN superlattices

K. S. Cho, Y. F. Chen, Y. Q. Tang, and B. Shen

Appl. Phys. Lett. 90, 041909 (2007); http://dx.doi.org/10.1063/1.2435591 (3 pages) | Cited 15 times

Online Publication Date: 23 January 2007

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The linear and circular photogalvanic effects (CPGEs), induced by ultraviolet (325 nm) radiation, have been observed in the (0001)-oriented Al0.15Ga0.85N/GaN superlattices. The CPGE current changes sign upon reversing the radiation helicity, and it is up to two orders of magnitude larger than that obtained by far-infrared radiation. This result suggests the existence of a sizeable Rashba spin splitting in AlGaN/GaN superlattices. It also provides a possibility for the generation of spin orientation-induced current at room temperature.
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72.40.+w Photoconduction and photovoltaic effects
73.63.-b Electronic transport in nanoscale materials and structures

Evolution of W optical center in Si-implanted epitaxial SiGe at low temperature annealing

J. Tan, G. Davies, S. Hayama, and A. Nylandsted Larsen

Appl. Phys. Lett. 90, 041910 (2007); http://dx.doi.org/10.1063/1.2435976 (3 pages)

Online Publication Date: 24 January 2007

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The authors have investigated the effect of Ge concentration on the evolution of W optical center (W center) in Si-implanted epitaxial Si1−xGex at low temperature annealing. From the results of photoluminescence, the annealing behavior of W center can be separated into two regimes, i.e., W centers in Si1−xGex alloy with Ge <5% are stable, otherwise not stable. The annealing behavior of W center is similar to {311} defect in Si1−xGex. It is suggested that the dissipation of excess interstitials by outdiffusion at low temperature is one of the candidate mechanisms for the retardation of transient enhanced diffusion of boron in Si1−xGex.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.55.Hx Other solid inorganic materials
66.30.J- Diffusion of impurities
71.55.Ht Other nonmetals

Multidirectional observation of an embedded quantum dot

Takashi Kita, Tomoya Inoue, Osamu Wada, Mitsuru Konno, Toshie Yaguchi, and Takeo Kamino

Appl. Phys. Lett. 90, 041911 (2007); http://dx.doi.org/10.1063/1.2436633 (3 pages) | Cited 4 times

Online Publication Date: 24 January 2007

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The authors succeeded in observing atomic scale images of undamaged single InAs quantum dots (QDs) embedded in the GaAs matrix using high resolution transmission electron microscope equipped with focused ion beam system. The QD can be viewed from multidirections, and a conclusive and comprehensible determination of the size and the shape anisotropy has been realized. Asymmetry of the structural properties has been confirmed between the [110] and [−110] crystal directions. The embedded QD is elongated along the [−110] axis. The strain-field pattern is also asymmetric according to the shape anisotropy. The results will enable the investigation of the exact structure anisotropy influencing the atomlike properties of QDs.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Lp Transmission electron microscopy (TEM)

Grain boundary impurity and porosity effects on the yield strength of nanocrystalline materials

James C. M. Li

Appl. Phys. Lett. 90, 041912 (2007); http://dx.doi.org/10.1063/1.2430491 (3 pages) | Cited 5 times

Online Publication Date: 25 January 2007

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The effect of impurities on the equilibrium and nonequilibrium boundaries is analyzed for nanocrystalline materials. Due to the purity of equilibrium grain boundaries, the strength levels off to a limiting value in the range of nano grain sizes. This limiting value increases with the total impurity content. Due to nonequilibrium grain boundaries and their effect on impurity segregation, the strength may decrease with decreasing grain size in the nanosize regime. These considerations can explain all the observed effects of grain size on strength without invoking other mechanisms for the nanosize grains. By controlling the impurity content and porosity of the grain boundaries, it is possible to synthesize ultrastrong and ductile materials.
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81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
61.46.Hk Nanocrystals
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
81.40.Lm Deformation, plasticity, and creep

Self-organized nanocrystalline stripe patterns generated during early crystallization of a nonequilibrium metallic glass

Jian-Min Li

Appl. Phys. Lett. 90, 041913 (2007); http://dx.doi.org/10.1063/1.2436707 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2007

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The author reports a unique early-stage (the crystallized volume fraction ∼ 0.20) self-organized nanocrystalline stripe pattern phenomenon that nanoscale phase separation and nucleation simultaneously work together, representing a type that had never been previously observed in a metastable alloy solid. The first observation of mesoscopic self-organized crystallization showed that self-organization is not limited to the case of organic matter, thus potentially offering an insight into the mechanism of the nonequilibrium (nano)crystallization of metallic glasses.
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81.05.Kf Glasses (including metallic glasses)
81.16.Dn Self-assembly
61.43.Fs Glasses
64.60.Q- Nucleation
64.75.-g Phase equilibria

Random surface roughness influence on gas damped nanoresonators

G. Palasantzas

Appl. Phys. Lett. 90, 041914 (2007); http://dx.doi.org/10.1063/1.2435328 (3 pages) | Cited 7 times

Online Publication Date: 25 January 2007

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The author investigates quantitatively the influence of random surface roughness on the quality factor Q of nanoresonators due to noise by impinging gas molecules. The roughness is characterized by the amplitude w, the correlation length ξ, and the roughness exponent H that describes fine roughness details at short wavelengths. Surface roughening (decreasing H and increasing ratio w/ξ) leads to lower Q, which translates to lower sensitivity to external perturbations, and a higher limit to mass sensitivity. The influence of the exponent H is shown to be important as that of w/ξ, indicating the necessity for precise control of the surface morphology.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
68.35.B- Structure of clean surfaces (and surface reconstruction)

Domain wall broadening mechanism for domain size effect of enhanced piezoelectricity in crystallographically engineered ferroelectric single crystals

Wei-Feng Rao and Yu U. Wang

Appl. Phys. Lett. 90, 041915 (2007); http://dx.doi.org/10.1063/1.2435584 (3 pages) | Cited 16 times

Online Publication Date: 25 January 2007

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Computer modeling and simulation reveal a domain wall broadening mechanism that explains the domain size effect of enhanced piezoelectric properties in domain engineered ferroelectric single crystals. The simulation shows that, under electric field applied along the nonpolar axis of single crystal without domain wall motion, the domain wall broadens and serves as embryo of field-induced new phase, producing large reversible strain free from hysteresis. This mechanism plays a significant role in the vicinity of interferroelectric transition temperature and morphotropic phase boundary, where energy difference between stable and metastable phases is small. Engineered domain configuration fully exploits this domain wall broadening mechanism.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.65.-j Piezoelectricity and electromechanical effects

Ground and excited state transitions in as-grown Ga0.64In0.36N0.046As0.954 quantum wells studied by contactless electroreflectance

Robert Kudrawiec, Marta Gladysiewicz, Jan Misiewicz, Fumitaro Ishikawa, and Klaus H. Ploog

Appl. Phys. Lett. 90, 041916 (2007); http://dx.doi.org/10.1063/1.2432230 (3 pages) | Cited 9 times

Online Publication Date: 26 January 2007

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The optical transitions of as-grown Ga0.64In0.36N0.046As0.954 multiple quantum wells grown at the low temperature of 375 °C were studied by contactless electroreflectance (CER). The investigation was carried out at room temperature for a set of samples having quantum well (QW) widths ranging from 3.9 to 8.1 nm. The ground and the excited state transitions were clearly observed in CER spectra (the ground state transition was observed at the wavelength of 1.9 μm for the 8.1 nm wide QW). The experimental QW transition energies were compared with theoretical predictions based on an effective mass formalism model. Good agreement between experimental data and theoretical calculations has been obtained assuming that the conduction band offset for GaInNAs/GaAs interface is 80% and the electron effective mass is 0.09m0.
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78.67.De Quantum wells
78.20.Jq Electro-optical effects
73.63.Hs Quantum wells
73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Complex excitonic recombination kinetics in ZnO: Capture, relaxation, and recombination from steady state

F. Bertram, J. Christen, A. Dadgar, and A. Krost

Appl. Phys. Lett. 90, 041917 (2007); http://dx.doi.org/10.1063/1.2432259 (3 pages) | Cited 15 times

Online Publication Date: 26 January 2007

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The kinetics of relaxation and recombination processes of excitons in an epitaxial-grown thick ZnO layer has been examined using time-resolved cathodoluminescence. The unique feature of this technique allows the full analysis of excitation from thermal equilibrium into true steady state and the relaxation back into thermal equilibrium. The luminescence at 5 K is characterized by a rich structure of excitonic lines: XA, I1, I2, I6, I8, and I9 as well as the excited states I6*, I8*, and I9* are clearly resolved. The efficient capture of the free excitons by impurities is directly visualized during the onset as well as the decay. This capture feeds the neutral impurity bound excitons I8 and I9, the initial decay of which becomes delayed. The ionized impurity bound excitons I1 and I2 exhibit a very fast initial decay due to the carrier capture by the impurities followed by a persistent, significantly slower nonexponential component.
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73.61.Ga II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.60.Hk Cathodoluminescence, ionoluminescence

In situ growth regime characterization of cubic GaN using reflection high energy electron diffraction

J. Schörmann, S. Potthast, D. J. As, and K. Lischka

Appl. Phys. Lett. 90, 041918 (2007); http://dx.doi.org/10.1063/1.2432293 (3 pages) | Cited 17 times

Online Publication Date: 26 January 2007

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Cubic GaN layers were grown by plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. In situ reflection high energy electron diffraction was used to quantitatively determine the Ga coverage of the GaN surface during growth. Using the intensity of the electron beam as a probe, optimum growth conditions of c-GaN were found when a 1 ML Ga coverage is formed at the surface. 1 μm thick c-GaN layers had a minimum surface roughness of 2.5 nm when a Ga coverage of 1 ML was established during growth. These samples revealed also a minimum full width at half maximum of the (002) rocking curve.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)

Raman study of thermochromic phase transition in tungsten trioxide nanowires

Dong Yu Lu, Jian Chen, Huan Jun Chen, Li Gong, Shao Zhi Deng, Ning Sheng Xu, and Yu Long Liu

Appl. Phys. Lett. 90, 041919 (2007); http://dx.doi.org/10.1063/1.2435616 (3 pages) | Cited 18 times

Online Publication Date: 26 January 2007

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Tungsten trioxide (WO3) nanowires were synthesized by thermal evaporation of tungsten powder in two steps: tungsten suboxide (WO3−x) nanowires were synthesized, and then oxidized in O2 ambient and transformed into WO3 nanowires. Raman spectroscopy was applied to study the thermochromic phase transition of one-dimensional WO3 nanowires. From the temperature dependence of the characteristic mode at 33 cm−1 in WO3, the phase transition temperature was determined. It was found that the phase transition of WO3 nanowires was reversible and the phase transition temperatures were even lower than that of WO3 nanopowder.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.30.Hv Other nonmetallic inorganics

Metallic phase transition investigated via terahertz time-domain spectroscopy

K. J. Chau, K. M. Rieckmann, and A. Y. Elezzabi

Appl. Phys. Lett. 90, 041920 (2007); http://dx.doi.org/10.1063/1.2432299 (3 pages)

Online Publication Date: 26 January 2007

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Terahertz time-domain spectroscopy is applied to noninvasively investigate the solid-liquid phase transition of metallic gallium (Ga) microparticles over the temperature range from 21.2 to 38.2 °C. Fourier and correlation analyses of the transmitted radiation reveal solid-liquid phase transformation at the melting transition temperature Tm and particle conglomeration at a temperature Tc>Tm.
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64.70.D- Solid-liquid transitions
78.70.Gq Microwave and radio-frequency interactions
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Magnetotransport through two dimensional electron gas in a tubular geometry

Nakul Shaji, Hua Qin, Robert H. Blick, Levente J. Klein, Christoph Deneke, and Oliver G. Schmidt

Appl. Phys. Lett. 90, 042101 (2007); http://dx.doi.org/10.1063/1.2433040 (3 pages) | Cited 14 times

Online Publication Date: 22 January 2007

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The authors report on topology dependent electron transport in tubular shaped two dimensional electron gas. These micron sized tubes are realized in strained InGaAs quantum wells as a first step towards investigating geometric potentials in low dimensional quantum systems. They investigate the topology induced change in magnetoresistance of the electronic system in a perpendicular magnetic field. At low magnetic field, an increased zero field magnetoresistance followed by a negative magnetoresistance is observed. They ascribe this effect to an increase in electron scattering along the curved regions. At high magnetic fields they observe a linear increase in resistance of the curved region as compared to planar regions.
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73.63.Hs Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
68.65.Fg Quantum wells

Anomalously anisotropic channel mobility on trench sidewalls in 4H-SiC trench-gate metal-oxide-semiconductor field-effect transistors fabricated on 8° off substrates

Hiroshi Yano, Hiroshi Nakao, Hidenori Mikami, Tomoaki Hatayama, Yukiharu Uraoka, and Takashi Fuyuki

Appl. Phys. Lett. 90, 042102 (2007); http://dx.doi.org/10.1063/1.2434157 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2007

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Metal-oxide-semiconductor (MOS) channel properties in 4H-SiC trench-gate MOS field-effect transistors fabricated on 8° off substrates were characterized. The MOS channel was formed only on one side of the trench sidewalls. The MOS field effect transistor performance depended strongly on the MOS channel planes of (11math0), (mathmath20), (1math00), and (math100). The highest channel mobility of 43 cm2/V s was obtained on (11math0). However, only a half value of 21 cm2/V s was observed on (mathmath20), which is the opposite face to (11math0). The anomalously anisotropic channel mobility is discussed based on the deviation from the crystallographically accurate {11math0} plane caused by the combination of substrate off angle and sloped trench sidewalls.
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85.30.Tv Field effect devices

Preparation of ZnO substrates for epitaxy: Structural, surface, and electrical properties

S. Graubner, C. Neumann, N. Volbers, B. K. Meyer, J. Bläsing, and A. Krost

Appl. Phys. Lett. 90, 042103 (2007); http://dx.doi.org/10.1063/1.2434170 (3 pages) | Cited 24 times

Online Publication Date: 24 January 2007

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The authors investigate the influence of a high temperature annealing in O2 atmosphere on the structural properties of ZnO substrates. Only at temperatures above 1100 °C are atomic step heights and terraces seen by atomic force microscopy. The structural properties of the substrates were determined from the full width at half maximum (FWHM) of the rocking curve of the (0002) reflection. The FWHM is between 28 and 33 arc sec for different substrates cut from one ingot but does not change with the annealing. The electrical properties, however, change from highly resistive to n-type conductive, which makes the substrates suitable for top-to-bottom contacting.
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
72.80.Ey III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Accurate measurement of extremely low surface recombination velocities on charged, oxidized silicon surfaces using a simple metal-oxide-semiconductor structure

W. E. Jellett and K. J. Weber

Appl. Phys. Lett. 90, 042104 (2007); http://dx.doi.org/10.1063/1.2434172 (3 pages) | Cited 9 times

Online Publication Date: 24 January 2007

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The authors report a simple technique to determine the surface recombination velocity of silicon and other semiconductor surfaces which have been passivated with a dielectric layer, as a function of charge density. A metal-oxide-semiconductor structure, employing large area, partially transparent metal contacts, is used to enable the charging of the surfaces. Simultaneous measurement of the emitter saturation current density Joe and the effective instantaneous lifetime τinst allows accurate extraction of the effective surface recombination velocity Seff at any given injection level. Extremely low Joe values of 1.8 fA cm−2 are measured on the silicon-silicon oxide (Si–SiO2) interface of a thermally oxidized, charged wafer.
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72.80.Cw Elemental semiconductors
73.25.+i Surface conductivity and carrier phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Stress induced leakage current mechanism in thin Hf-silicate layers

A. Paskaleva, M. Lemberger, and A. J. Bauer

Appl. Phys. Lett. 90, 042105 (2007); http://dx.doi.org/10.1063/1.2420774 (3 pages) | Cited 6 times

Online Publication Date: 24 January 2007

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Stress induced leakage current (SILC) in thin Hf-silicate layers and the mechanisms of its creation are examined. A very strong polarity and thickness dependence as well as partial recovery of SILC are observed. It is suggested that the trapping in preexisting sites influences SILC by two ways: (1) it could be the first stage of defect generation mechanism leading to the permanent component of SILC and (2) it is fully responsible for the partial recovery of SILC. Therefore, the origin of SILC in Hf silicate is distinctly different from that of SiO2. The physical origin of the preexisting sites is also discussed.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
77.55.-g Dielectric thin films

Conductive atomic force microscopy study of silica nanotrench structure

Z. G. Sun, H. Kuramochi, H. Akinaga, H. H. Yu, and E. D. Gu

Appl. Phys. Lett. 90, 042106 (2007); http://dx.doi.org/10.1063/1.2436709 (3 pages)

Online Publication Date: 25 January 2007

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Conductive atomic force microscope had been applied to study the electrical transportation mechanism together with topographic information on a periodical silica nanotrench structure. The bottom of the trench is covered by a 4 nm silica thin film, while the ridges between the trenches are made up of 90 nm thick silica film. On the same bias, the current transport through the bottom is larger than the current transport through the ridges. In the bottom, rectifying characteristics are observed; the conduction mechanism can be ascribed as a Schottky emission. Strong inhomogeneous electrical properties are also observed. A high resolution with a lateral resolution below 6 nm is demonstrated in the conductive atomic force microscope study.
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61.46.-w Structure of nanoscale materials
72.80.Sk Insulators

Reproducible hysteresis and resistive switching in metal-CuxO-metal heterostructures

R. Dong, D. S. Lee, W. F. Xiang, S. J. Oh, D. J. Seong, S. H. Heo, H. J. Choi, M. J. Kwon, S. N. Seo, M. B. Pyun, M. Hasan, and Hyunsang Hwang

Appl. Phys. Lett. 90, 042107 (2007); http://dx.doi.org/10.1063/1.2436720 (3 pages) | Cited 69 times

Online Publication Date: 25 January 2007

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Materials showing reversible resistance switching between high-resistance state and low-resistance state at room temperature are attractive for today’s semiconductor technology. In this letter, the reproducible hysteresis and resistive switching characteristics of metal-CuxO-metal (M-CuxO-M) heterostructures driven by low voltages are demonstrated. The fabrication of the M-CuxO-M heterostructures is fully compatible with the standard complementary metal-oxide semiconductor process. The hysteresis and resistive switching behavior are discussed. The good retention characteristics are exhibited in the M-CuxO-M heterostructures by the accurate controlling of the preparation parameters.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Comparison of electronic structures of RuO2 and IrO2 nanorods investigated by x-ray absorption and scanning photoelectron microscopy

H. M. Tsai, P. D. Babu, C. W. Pao, J. W. Chiou, J. C. Jan, K. P. Krishna Kumar, F. Z. Chien, W. F. Pong, M.-H. Tsai, C.-H. Chen, L. Y. Jang, J. F. Lee, R. S. Chen, Y. S. Huang, and D. S. Tsai

Appl. Phys. Lett. 90, 042108 (2007); http://dx.doi.org/10.1063/1.2430929 (3 pages)

Online Publication Date: 25 January 2007

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Electronic structures of the nanorods of RuO2 and IrO2 metallic oxides were investigated by x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM). O K-, Ru, and Ir L3-edge XANES results reveal that hybridization between O 2p and metal t2g orbitals is weaker in IrO2 than in RuO2. The enhancement of the tip-region SPEM intensities relative to those in the sidewall regions for both RuO2 and IrO2 nanorods is found to extend over a large energy range in contrast to those of carbon nanotubes and ZnO nanorods, which are confined to deep below and near the Fermi level, respectively.
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73.22.Dj Single particle states
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Room-temperature oxygen sensitivity of ZnS nanobelts

Y. G. Liu, P. Feng, X. Y. Xue, S. L. Shi, X. Q. Fu, C. Wang, Y. G. Wang, and T. H. Wang

Appl. Phys. Lett. 90, 042109 (2007); http://dx.doi.org/10.1063/1.2432278 (3 pages) | Cited 25 times

Online Publication Date: 26 January 2007

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Room-temperature oxygen sensing is realized from individual ZnS nanobelts. Under UV illumination the current through ZnS nanobelt increases from 0.265 to 2.26 nA as the oxygen pressure decreases from 1×105 to 3×10−3 Pa. The conductance of ZnS nanobelt exhibits a logarithmic dependence on oxygen pressure, which is in agreement with theoretical prediction. The sensing is based on the enhanced modulation of ZnS nanobelts conductance by adsorbed oxygen under illumination. These results demonstrate an approach to in situ precisely detect oxygen at room temperature.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.63.Bd Nanocrystalline materials

Photoluminescence study of an ultrathin strained silicon on insulator layer

J. Munguía, G. Bremond, J. de la Torre, and J.-M. Bluet

Appl. Phys. Lett. 90, 042110 (2007); http://dx.doi.org/10.1063/1.2432290 (3 pages) | Cited 8 times

Online Publication Date: 26 January 2007

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Low temperature photoluminescence has been performed in order to analyze the strain effect on the Si band structure for an 8 nm thick tensile strained silicon layer on insulator. The authors show three phonon assisted optical transitions related to the strained silicon top layer at 0.923, 0.983, and 1.022 eV. The 0.983 eV line of the TO phonon assisted transition corresponds to a 115 meV strain induced band gap shrinkage at Δ point which agrees with the calculated values of strained silicon band gap.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
71.20.Mq Elemental semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Abruptness of a-Si:H/c-Si interface revealed by carrier lifetime measurements

Stefaan De Wolf and Michio Kondo

Appl. Phys. Lett. 90, 042111 (2007); http://dx.doi.org/10.1063/1.2432297 (3 pages) | Cited 25 times

Online Publication Date: 26 January 2007

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Intrinsic hydrogenated amorphous silicon films can yield outstanding electronic surface passivation of crystalline silicon wafers. In this letter the authors confirm that this is strongly determined by the abruptness of the interface. For completely amorphous films the passivation quality improves by annealing at temperatures up to 260 °C, most likely by film relaxation. This is different when an epitaxial layer has been grown at the interface during film deposition. Annealing is in such a case detrimental for the passivation. Consequently, the authors argue that annealing followed by carrier lifetime measurements allows determining whether the interface is abrupt.
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68.35.Ct Interface structure and roughness
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Cy Elemental semiconductors
81.65.Rv Passivation
61.72.Cc Kinetics of defect formation and annealing

Study of the effects of an AlN interlayer on the transport properties of AlGaN/AlN/GaN heterostructures grown on SiC

S. Elhamri, W. C. Mitchel, W. D. Mitchell, G. R. Landis, R. Berney, and A. Saxler

Appl. Phys. Lett. 90, 042112 (2007); http://dx.doi.org/10.1063/1.2432300 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2007

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Transport measurements were used to characterize AlGaN/AlN/GaN/SiC. While the carrier concentration, n = 9.2×1012 cm−2, remained relatively unchanged from 300 down to 1.2 K, the mobility increased from 2100 to over 3×104 cm2/V s. Shubnikov-de Haas oscillations were observed in fields as low as 2 T. Despite the high n, quantum Hall plateaus, which are rarely reported in conventional AlGaN/GaN with comparable n, were observed. The calculated quantum scattering time of 0.28 ps is longer than what is typically reported for conventional AlGaN/GaN. This improvement is believed to be due to a reduction in alloy scattering.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
73.43.-f Quantum Hall effects

Room temperature p-n ZnO blue-violet light-emitting diodes

Z. P. Wei, Y. M. Lu, D. Z. Shen, Z. Z. Zhang, B. Yao, B. H. Li, J. Y. Zhang, D. X. Zhao, X. W. Fan, and Z. K. Tang

Appl. Phys. Lett. 90, 042113 (2007); http://dx.doi.org/10.1063/1.2435699 (3 pages) | Cited 63 times

Online Publication Date: 26 January 2007

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ZnO p-n junction light-emitting diodes (LEDs) were fabricated on c-plane Al2O3 substrates by plasma-assisted molecular beam epitaxy. Gas mixture of N2 and O2 was used as the p-type dopant, by which the double-donor doping of N2(O) can be avoided significantly. The fabricated p-type ZnO layers have a higher hole density and carrier mobility. The LEDs showed a very good rectification characteristic with a low threshold voltage of 4.0 V even at a temperature above 300 K. The LEDs can even emit intensive electroluminescence in the blue-violet region at the temperature of 350 K. The blue-violet emission was attributed to the donor-acceptor pair recombination at the p-type layer of the LED.
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85.60.Jb Light-emitting devices
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