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1 Mar 2004

Volume 84, Issue 9, pp. 1435-1613

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1558 (2004); http://dx.doi.org/10.1063/1.1651641 (3 pages)

DongWeon Lee, Adrian Wetzel, Roland Bennewitz, Ernst Meyer, Michel Despont, Peter Vettiger, and Christoph Gerber
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Nonlinear emission in II–VI pillar microcavities: Strong versus weak coupling

M. Obert, J. Renner, A. Forchel, G. Bacher, R. André, and D. Le Si Dang

Appl. Phys. Lett. 84, 1435 (2004); http://dx.doi.org/10.1063/1.1651646 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2004

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Pillar microcavities based on CdMnTe/CdMgTe heterostructures have been investigated by means of spatially resolved optical spectroscopy. Strong coupling with a Rabi splitting of about 15.8 meV is demonstrated by performing microreflectivity measurements on a single pillar with three-dimensional optical confinement. Analyzing the temperature and the power dependent photoluminescence signal after nonresonant excitation, clear evidence of strong coupling in the nonlinear emission regime is obtained even at elevated temperatures. © 2004 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Enhanced Faraday rotation in all-garnet magneto-optical photonic crystal

S. Kahl and A. M. Grishin

Appl. Phys. Lett. 84, 1438 (2004); http://dx.doi.org/10.1063/1.1651324 (3 pages) | Cited 42 times

Online Publication Date: 25 February 2004

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Research on magneto-optical photonic crystals has so far been focused on theoretical investigations, because suitable multilayers of iron garnet, the most promising material, have not been readily available. We report the preparation and characterization of a one-dimensional magneto-optical photonic crystal composed of 17 heteroepitaxial layers of bismuth iron garnet and yttrium iron garnet. The magneto-optical Faraday rotation was increased by 140% while transmission decreased by just 16% at the design wavelength of 750 nm as compared with a single-layer bismuth iron garnet film of equivalent thickness. The sample is free of cracks, and good agreement of simulated and experimental spectra of optical transmission and Faraday rotation indicate high quality of the sample and robustness of the preparation technique. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
81.15.Fg Pulsed laser ablation deposition
68.65.Cd Superlattices
78.20.Ls Magneto-optical effects
75.50.Gg Ferrimagnetics

Morphology of femtosecond laser-induced structural changes in bulk transparent materials

Chris B. Schaffer, Alan O. Jamison, and Eric Mazur

Appl. Phys. Lett. 84, 1441 (2004); http://dx.doi.org/10.1063/1.1650876 (3 pages) | Cited 62 times

Online Publication Date: 25 February 2004

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Using optical and electron microscopy, we analyze the energy and focusing angle dependence of structural changes induced in bulk glass by tightly focused femtosecond laser pulses. We observe a transition from small density variations in the material to void formation with increasing laser energy. At energies close to the threshold for producing a structural change, the shape of the structurally changed region is determined by the focal volume of the objective used to focus the femtosecond pulse, while at higher energies, the structural change takes on a conical shape. From these morphological observations, we infer the role of various mechanisms for structural change. © 2004 American Institute of Physics.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

High-impedance reflectivity and surface-wave band gaps in metamaterials

Lei Zhou and C. T. Chan

Appl. Phys. Lett. 84, 1444 (2004); http://dx.doi.org/10.1063/1.1652236 (3 pages) | Cited 13 times

Online Publication Date: 25 February 2004

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We studied the surface wave and reflective properties of two types of metamaterials, one that combines a material with dispersive μ with a metal film, and another that possesses arbitrary ε and μ. Generic surface wave phase diagrams with respect to ε and μ are given. For the first type, we find that the simultaneous appearance of high-impedance reflectivity and a surface-wave gap requires additional mechanisms such as Bragg scattering, while metamaterials of the second type can possess high surface impedance and a surface-wave gap simultaneously. © 2004 American Institute of Physics.
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42.25.Gy Edge and boundary effects; reflection and refraction
73.25.+i Surface conductivity and carrier phenomena

λ ∼ 4–5.3 μm intersubband emission from InGaAs–AlAsSb quantum cascade structures

D. G. Revin, L. R. Wilson, E. A. Zibik, R. P. Green, J. W. Cockburn, M. J. Steer, R. J. Airey, and M. Hopkinson

Appl. Phys. Lett. 84, 1447 (2004); http://dx.doi.org/10.1063/1.1655691 (3 pages) | Cited 11 times

Online Publication Date: 25 February 2004

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The In0.53Ga0.47As–AlAs0.56Sb0.44 materials system, lattice matched to InP, is an attractive candidate for short wavelength quantum cascade lasers due to the very large conduction band discontinuity (∼1.6 eV) and compatibility with well established quantum cascade laser waveguide design and fabrication technology. In this letter we report the operation of In0.53Ga0.47As–AlAs0.56Sb0.44 quantum cascade structures emitting in the wavelength range λ ∼ 4–5.3 μm. Clear intersubband electroluminescence peaks are observed close to the design wavelengths, with full widths at half maximum in the range of ∼30–40 meV. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Fi Electroluminescence

Nonlinear optical properties of an organic film formed of dye aggregates with absorption in the telecommunication wavelength range

Satoshi Tatsuura, Minquan Tian, Makoto Furuki, Yasuhiro Sato, Izumi Iwasa, and Hiroyuki Mitsu

Appl. Phys. Lett. 84, 1450 (2004); http://dx.doi.org/10.1063/1.1652234 (3 pages) | Cited 15 times

Online Publication Date: 25 February 2004

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An organic film formed of newly synthesized dye aggregates with an absorption peak in telecommunication wavelength range exhibited large third-order nonlinear optical susceptibility χ(3) and fast recovery of bleached absorption. A derivative with a di(benzofuranonyl)methanolate structure forms stable aggregates in a spin-coated film and shows an absorption maximum at 1.24 μm. An imaginary part χI(3) of the film assumes a maximum at 1.30 μm, which is −0.83×10−7 esu. The time evolution of differential transmission spectra indicates that the time constant of the recovery of bleached absorption is 80–240 fs for a fast component and 2.2–6.5 ps for a slow one. This organic film has considerable advantages for future planar optical devices. © 2004 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
78.66.Qn Polymers; organic compounds
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Wc Optical coatings

Measurement of the effective electron mass in GaInNAs by energy-loss spectroscopy

M. H. Gass, A. J. Papworth, T. B. Joyce, T. J. Bullough, and P. R. Chalker

Appl. Phys. Lett. 84, 1453 (2004); http://dx.doi.org/10.1063/1.1650906 (3 pages) | Cited 13 times

Online Publication Date: 25 February 2004

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Imaging of the electronic structure of a GaInNAs/GaAs quantum well has been investigated by mapping the variation in the plasmon frequency using an electron energy-loss spectrometer on a dedicated field emission gun scanning transmission electron microscope. Kramers–Kronig analysis of the single scattered low-loss region yields a measure of the joint effective valence electron density. The average electron density has been used to provide a direct measurement of the electron effective mass of GaInNAs. The reduced mass was found to be 0.0874m0 for a 7 nm thick Ga0.9In0.1N0.04As0.96 quantum well. © 2004 American Institute of Physics.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.21.Fg Quantum wells
79.20.Uv Electron energy loss spectroscopy
68.37.Lp Transmission electron microscopy (TEM)

Measurements of charge mobility and diffusion coefficient of conjugated electroluminescent polymers by time-of-flight method

Hao-En Tseng, Tzu-Hao Jen, Kang-Yung Peng, and Show-An Chen

Appl. Phys. Lett. 84, 1456 (2004); http://dx.doi.org/10.1063/1.1655700 (3 pages) | Cited 12 times

Online Publication Date: 25 February 2004

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Charge mobilities (μ) and diffusion coefficients (D) of hole (μh, Dh) and electron (μe, De) of the conjugated electroluminescent polymers, poly(phenylene vinylene)s and polyfluorenes, have been measured by fitting of a theoretical photocurrent transient equation to time-of-flight photocurrent transients. The μ so obtained are in agreement with those from inflection points of photocurrent transients. The D value lumps all factors together that cause the dispersion of carriers, and the parameter Dq/μkT can be used as an indicator of the degree of dispersion. This fitting method allows extracting μ and D from highly dispersive photocurrent transients, even for the case in which no inflection point appears. © 2004 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Fr Low-field transport and mobility; piezoresistance
78.60.Fi Electroluminescence
72.40.+w Photoconduction and photovoltaic effects

Electroluminescence of single silicon nanocrystals

Jan Valenta, Nenad Lalic, and Jan Linnros

Appl. Phys. Lett. 84, 1459 (2004); http://dx.doi.org/10.1063/1.1655705 (3 pages) | Cited 34 times

Online Publication Date: 25 February 2004

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We report on measurements of room-temperature electroluminescence from single silicon nanocrystals. The electrically driven emission reveals typical characteristics of single-nanocrystal luminescence: the peak wavelength variations, narrowing of spectral bands, a high degree of linear polarization, and intensity fluctuations (blinking) observed on a scale of minutes. From the count rate statistics of individual nanocrystals, we conclude that the yield of radiative emission is as high as 19%. These findings may open a route to highly efficient all-silicon light emitters. © 2004 American Institute of Physics.
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81.05.Cy Elemental semiconductors
85.60.Jb Light-emitting devices
81.07.Bc Nanocrystalline materials
78.60.Fi Electroluminescence
61.46.-w Structure of nanoscale materials

Optical amplification and electroluminescence at 1.54 μm in Er-doped zinc silicate germanate on silicon

C. C. Baker, J. Heikenfeld, Z. Yu, and A. J. Steckl

Appl. Phys. Lett. 84, 1462 (2004); http://dx.doi.org/10.1063/1.1651655 (3 pages) | Cited 16 times

Online Publication Date: 25 February 2004

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Optical amplification and electroluminescence at 1.5 μm is reported in Er-doped Zn2Si0.5Ge0.5O4 (ZSG:Er) on silicon. ZSG:Er films were deposited by rf sputtering from a composite target in Ar/O2 mixtures. Channel waveguides were fabricated by plasma etching with Cl/Ar. The refractive index of ZSG:Er was found to be 1.75 at 1.54 μm. Signal enhancement greater than 13 dB and an internal gain of ∼ 2 dB have been achieved by optically pumping a 4.7 cm ZSG:Er amplifier. Electroluminescence at 1.5 μm was achieved using an ac device structure with a ZSG:Er central layer and upper and lower dielectric layers. © 2004 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Li Other semiconductors
42.79.Gn Optical waveguides and couplers
61.72.S- Impurities in crystals
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
81.65.Cf Surface cleaning, etching, patterning
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
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Vertical alignment liquid crystal cell with optically compensated splay configuration of the liquid crystal

S. H. Lee, S. J. Kim, and J. C. Kim

Appl. Phys. Lett. 84, 1465 (2004); http://dx.doi.org/10.1063/1.1652230 (3 pages) | Cited 5 times

Online Publication Date: 25 February 2004

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We have observed a phenomenon associated with a transition from vertical alignment to an optically compensated splay structure. With rubbed homeotropic alignment in parallel directions, the device shows vertical alignment but the liquid crystals (LCs) are twisted 180° in the absence of an electric field. Depending on the voltage applied, two different configurations of LCs are possible. After applying a critical voltage, the LC configuration becomes splayed such that the middirector lies parallel to the substrate and around it, and a hybrid structure forms symmetrically. A method for obtaining the transition and the electro-optic characteristics of the device is discussed. © 2004 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
78.20.Jq Electro-optical effects

Radio frequency potential of inductive plasma immersed in a weak magnetic field

V. A. Godyak and B. M. Alexandrovich

Appl. Phys. Lett. 84, 1468 (2004); http://dx.doi.org/10.1063/1.1655698 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2004

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Radio frequency potential has been revealed in inductively coupled plasma (ICP) immersed in a weak magnetic field. The rf plasma potential measured in a wide range of driving frequency and argon pressure reached tens of volts at a relatively weak magnetic field and was found falling with an increase in the driving frequency and gas pressure. The appearance of rf plasma potential in magnetized ICP is interpreted as a result of rf Hall effect caused by the electron rf drift in a crossed magnetic field. © 2004 American Institute of Physics.
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52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
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Phase stability of diamond nanocrystals upon pulsed-laser-induced liquid-solid interfacial reaction: Experiments and ab initio calculations

Cheng-Xin Wang, Yu-Hua Yang, Qiu-Xiang Liu, Guo-Wei Yang, Yu-Liang Mao, and Xiao-Hong Yan

Appl. Phys. Lett. 84, 1471 (2004); http://dx.doi.org/10.1063/1.1650917 (3 pages) | Cited 4 times

Online Publication Date: 25 February 2004

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To clarify different phase formations of diamond nanocrystals upon pulsed-laser-induced liquid-solid interfacial reaction (PLIIR), we preformed the first-principles investigation of the total energy of cubic and hexagonal diamond. Interestingly, by a comparison of the structure stabilities of cubic and hexagonal diamond, we found that both cubic and hexagonal structures could form, simultaneously or one by one, upon those processes like as far-from equilibrium growth processes, such as PLIIR, due to the relatively small different of total energies and similar crystalline structures. Eventually, these calculations were in good agreement with the experimental results. © 2004 American Institute of Physics.
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64.70.D- Solid-liquid transitions
52.38.Mf Laser ablation
71.15.Nc Total energy and cohesive energy calculations
61.46.-w Structure of nanoscale materials

Improvement of crystalline silicon surface passivation by hydrogen plasma treatment

I. Martín, M. Vetter, A. Orpella, C. Voz, J. Puigdollers, R. Alcubilla, A. V. Kharchenko, and P. Roca i Cabarrocas

Appl. Phys. Lett. 84, 1474 (2004); http://dx.doi.org/10.1063/1.1647702 (3 pages) | Cited 6 times

Online Publication Date: 25 February 2004

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A completely dry low-temperature process has been developed to passivate 3.3 Ω cm p-type crystalline silicon surface with excellent results. Particularly, we have investigated the use of a hydrogen plasma treatment, just before hydrogenated amorphous silicon carbide (a-SiCx:H) deposition, without breaking the vacuum. We measured effective lifetime, τeff, through a quasi-steady-state photoconductance technique. Experimental results show that hydrogen plasma treatment improves surface passivation compared to classical HF dip. Seff values lower than 19 cm s−1 were achieved using a hydrogen plasma treatment and an a-SiCx:H film deposited at 300 °C. © 2004 American Institute of Physics.
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81.65.Rv Passivation
52.77.Bn Etching and cleaning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.Cf Surface cleaning, etching, patterning

Broadband emission and low absorption in microdisks with AlGaAs quantum wells

T. Kipp, K. Petter, Ch. Heyn, D. Heitmann, and C. Schüller

Appl. Phys. Lett. 84, 1477 (2004); http://dx.doi.org/10.1063/1.1651657 (3 pages) | Cited 5 times

Online Publication Date: 25 February 2004

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In microphotoluminescence measurements at room temperature on Al0.2Ga0.8As/Al0.4Ga0.6As multiple quantum well microdisks, we observe a large number of whispering gallery modes in a remarkably broad energy range of about 250 meV. This is in contrast to microdisks containing InGaAs or GaAs quantum wells, where typically only one or two whispering gallery modes are observed, but similar to the behavior of microdisks containing self-organized InAs quantum dots. We conclude that impurity levels below the recombination energy of free electron-hole pairs inside the alloy quantum wells lead to an efficient internal broadband emitter with low absorption. © 2004 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
78.67.De Quantum wells
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Mechanism of enhanced luminescence in InxAlyGa1−x−yN quaternary epilayers

C. H. Chen, Y. F. Chen, Z. H. Lan, L. C. Chen, K. H. Chen, H. X. Jiang, and J. Y. Lin

Appl. Phys. Lett. 84, 1480 (2004); http://dx.doi.org/10.1063/1.1650549 (3 pages) | Cited 17 times

Online Publication Date: 25 February 2004

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We report firm evidence for the underlying mechanism of the enhanced luminescence in InxAlyGa1−x−yN quaternary epilayers. Photoluminescence, Raman scattering, field emission scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), and cathodoluminescence (CL) measurements have been employed to study the correlation between optical and structural properties in these alloys. The phonon replica structures accompanying luminescence line, InGaN-related phonon modes in Raman spectra, SEM images, element composition analysis by EDS, and localized CL spectra provide the evidence to show that the existence of InGaN-like nanoclusters is responsible for the enhanced luminescence in InxAlyGa1−x−yN quaternary alloys. Our result therefore gives an excellent demonstration showing that because of the existence of nanoclusters a very defective alloy can exhibit a strong emission even at room temperature. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.60.Hk Cathodoluminescence, ionoluminescence
61.66.Fn Inorganic compounds
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Pulsed-electron-beam deposition of transparent conducting SnO2 films and study of their properties

R. J. Choudhary, S. B. Ogale, S. R. Shinde, V. N. Kulkarni, T. Venkatesan, K. S. Harshavardhan, M. Strikovski, and B. Hannoyer

Appl. Phys. Lett. 84, 1483 (2004); http://dx.doi.org/10.1063/1.1651326 (3 pages) | Cited 30 times

Online Publication Date: 25 February 2004

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Transparent conducting films of SnO2 are grown on single-crystal R-Al2O3 substrates by the pulsed electron beam deposition (PED) technique, and their electrical, optical, and microstructural properties are compared with the films grown by pulsed-laser deposition (PLD). In PED, the pulsed electron beam used for ablation is generated by a channel-spark system with discharge voltage of 12 kV, current ∼1 kA, and pulse duration of ∼100 ns. The PED films are highly oriented, show good epitaxy, and are highly transparent with transmittance of ∼80% in the visible and IR range. The measured band gap is close to 3.9 eV. It is shown that the PED film properties compare well with those of PLD films, with the 119Sn Mossbauer spectroscopy showing comparable local environments in the two. © 2004 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.66.Nk Insulators
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Influence of layer thickness on the formation of In vacancies in InN grown by molecular beam epitaxy

J. Oila, A. Kemppinen, A. Laakso, K. Saarinen, W. Egger, L. Liszkay, P. Sperr, H. Lu, and W. J. Schaff

Appl. Phys. Lett. 84, 1486 (2004); http://dx.doi.org/10.1063/1.1651327 (3 pages) | Cited 23 times

Online Publication Date: 25 February 2004

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We have used a low-energy positron beam to identify In vacancies in InN layers grown on Al2O3 by molecular beam epitaxy. Their concentration decreases from ∼ 5×1018 to below 1016 cm−3 with increasing layer thickness (120–800 nm). The decrease in the vacancy concentration coincides with the increase in the electron Hall mobility, suggesting that In vacancies act as electron scattering centers. © 2004 American Institute of Physics.
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61.72.J- Point defects and defect clusters
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Epitaxial GaN1−yAsy layers with high As content grown by metalorganic vapor phase epitaxy and their band gap energy

Akitaka Kimura, C. A. Paulson, H. F. Tang, and T. F. Kuech

Appl. Phys. Lett. 84, 1489 (2004); http://dx.doi.org/10.1063/1.1652232 (3 pages) | Cited 13 times

Online Publication Date: 25 February 2004

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GaN1−yAsy epitaxial alloy samples with [N]≫[As] were grown by metalorganic vapor phase epitaxy. The range of As content achieved, up to y = 0.067, greatly extends the range of achievable As levels to values that are well within the miscibility gap of the GaN–GaAs system. The single-phase epitaxial nature of the alloy samples was confirmed by x-ray diffraction. The As-content dependence of the band gap was determined by optical absorption measurements. A highly-bowed bandgap was observed as a function of the As content, and a refined value of the bowing parameter of 16.9±1.1 eV was determined. © 2004 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Ea III-V semiconductors

Comparative study of defect energetics in HfO2 and SiO2

W. L. Scopel, Antônio J. R. da Silva, W. Orellana, and A. Fazzio

Appl. Phys. Lett. 84, 1492 (2004); http://dx.doi.org/10.1063/1.1650874 (3 pages) | Cited 52 times

Online Publication Date: 25 February 2004

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We perform ab initio calculations, based on density functional theory, for substitutional and vacancy defects in the monoclinic hafnium oxide (m-HfO2) and α-quartz (SiO2). The neutral oxygen vacancies and substitutional Si and Hf defects in HfO2 and SiO2, respectively, are investigated. Our calculations show that, for a large range of Hf chemical potential, Si substitutional defects are most likely to form in HfO2, leading to the formation of a silicate layer at the HfO2/Si interface. We also find that it is energetically more favorable to form oxygen vacancies in SiO2 than in HfO2, which implies that oxygen-deficient HfO2 grown on top of SiO2 will consume oxygen from the SiO2. © 2004 American Institute of Physics.
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61.72.J- Point defects and defect clusters
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
65.40.G- Other thermodynamical quantities
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Properties of Ir-based Ohmic contacts to AlGaN/GaN high electron mobility transistors

R. C. Fitch, J. K. Gillespie, N. Moser, T. Jenkins, J. Sewell, D. Via, A. Crespo, A. M. Dabiran, P. P. Chow, A. Osinsky, J. R. La Roche, F. Ren, and S. J. Pearton

Appl. Phys. Lett. 84, 1495 (2004); http://dx.doi.org/10.1063/1.1651649 (3 pages) | Cited 12 times

Online Publication Date: 25 February 2004

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Measurement of the electrical characteristics of 250 devices on the same 2 in. diameter wafer shows that Ti/Al/Ir/Au Ohmic contacts on AlGaN/GaN high electron mobility transistors (HEMTs) have lower average specific contact resistance after annealing at 850 °C for 30 s (4.6×10−5 Ω cm2) compared to more standard Ti/Al/Ni/Au contacts (2×10−4 Ω cm2). HEMTs with these Ir-based contacts also show average interdevice isolation currents approximately a factor of 2 lower, higher peak transconductance (134 mS/mm compared to 121 mS/mm), and higher device breakdown voltage (31 V compared to 23 V) than the devices with Ni-based contacts. This Ir-based contact metallurgy looks promising for applications requiring extended thermal stability of the HEMTs. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
81.05.Ea III-V semiconductors

Effect of nitric oxide annealing on the interface trap density near the conduction bandedge of 4H–SiC at the oxide/(11math0) 4H–SiC interface

S. Dhar, Y. W. Song, L. C. Feldman, T. Isaacs-Smith, C. C. Tin, J. R. Williams, G. Chung, T. Nishimura, D. Starodub, T. Gustafsson, and E. Garfunkel

Appl. Phys. Lett. 84, 1498 (2004); http://dx.doi.org/10.1063/1.1651325 (3 pages) | Cited 25 times

Online Publication Date: 25 February 2004

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Nitric oxide postoxidation anneal results in a significant decrease of defect state density (Dit) near the conduction bandedge of n-4H–SiC at the oxide/(11math0) 4H–SiC interface. Comparison with measurements on the conventional (0001) Si-terminated face shows a similar interface state density following passivation. Medium energy ion scattering provides a quantitative measure of nitrogen incorporation at the SiO2/SiC interface. © 2004 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
61.72.Cc Kinetics of defect formation and annealing
81.65.Mq Oxidation
81.65.Rv Passivation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Electrical properties of Pt contacts on p-GaN activated in air

Yow-Jon Lin and Kuo-Chen Wu

Appl. Phys. Lett. 84, 1501 (2004); http://dx.doi.org/10.1063/1.1651658 (3 pages) | Cited 6 times

Online Publication Date: 25 February 2004

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In this study, the electrical properties of Pt contacts on p-type GaN (p-GaN) activated in air were investigated. From the observed photoluminescence result, it is suggested that the hydrogenated Ga vacancies (i.e., VGaH2) were formed during the activation process. However, VGaH2 in p-GaN near the surface was transformed into VGa after Pt deposition, because Pt strongly absorbed hydrogen. A large number of VGa at the Pt/p-GaN interface would lead to the pinning of the Fermi level at 0.3 eV above the valence-band edge, as well as the formation of the low barrier at the interface, and the formation of the nonalloyed ohmic contacts due to the occurrence of the tunneling transmission for holes at the interface. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
73.40.Ns Metal-nonmetal contacts
78.55.Cr III-V semiconductors

Low resistance and transparent Ni–La solid solution/Au ohmic contacts to p-type GaN

June-O Song, Dong-Seok Leem, J. S. Kwak, S. N. Lee, O. H. Nam, Y. Park, and Tae-Yeon Seong

Appl. Phys. Lett. 84, 1504 (2004); http://dx.doi.org/10.1063/1.1652238 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2004

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We report on the formation of reliable Ni–La solid solution (8 nm)/Au (8 nm) ohmic contacts to p-type GaN (Na = 5×1017 cm−3). The as-deposited contact reveals nonlinear current–voltage (I–V) characteristics. However, the contacts show considerably improved I–V behavior when annealed at temperatures of 350–550 °C for 1 min in air ambient. For example, the specific contact resistance as low as 7.2×10−5 Ω cm2 is obtained from the samples annealed at 550 °C, whose transmittance is measured to be 82.5% at a wavelength of 470 nm. Based on Auger electron spectroscopy and x-ray photoemission spectroscopy results, possible ohmic formation mechanisms for the annealed contacts are described and discussed. © 2004 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
79.20.Fv Electron impact: Auger emission

Electron scattering in AlGaN/GaN structures

S. Syed, M. J. Manfra, Y. J. Wang, R. J. Molnar, and H. L. Stormer

Appl. Phys. Lett. 84, 1507 (2004); http://dx.doi.org/10.1063/1.1655704 (3 pages) | Cited 18 times

Online Publication Date: 25 February 2004

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We present data on mobility lifetime τt, quantum lifetime τq, and cyclotron resonance lifetime τCR, of a sequence of high-mobility two-dimensional electron gases in the AlGaN/GaN system, covering a density range of 1 to 4.5×1012 cm−2. We observe a large discrepancy between τq and τCR(τq ∼ τCR/6), and explain it as the result of density fluctuations of only a few percent. Therefore, only τCR—and not τq—is a reliable measure of the time between electron-scattering events in these specimens. The ratio τt/τCR increases with increasing density in this series of samples, but scattering over this density range remains predominantly in the large-angle scattering regime. © 2004 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
68.35.Ct Interface structure and roughness
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
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