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21 Jun 1999

Volume 74, Issue 25, pp. 3755-3903

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Ab-initio calculation of excited state absorption of Cr4+ in Y3Al5O12

W. Y. Ching, Yong-Nian Xu, and B. K. Brickeen

Appl. Phys. Lett. 74, 3755 (1999); http://dx.doi.org/10.1063/1.124170 (3 pages) | Cited 14 times

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The Cr3+ and Cr4+ impurity states in Y3Al5O12 (YAG) crystal are studied by ab-initio supercell calculations using the density-functional theory. Calculations are carried out with Cr substitutions at the octahedral and tetrahedral Al sites including the effect of Ca co-doping. Optical transitions between various levels and to conduction band states are also calculated. A model for excited state absorption for Cr4+ in YAG is proposed. © 1999 American Institute of Physics.
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71.55.Ht Other nonmetals
75.50.Gg Ferrimagnetics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Low-resistance visible wavelength distributed Bragg reflectors using small energy band offset heterojunctions

J. M. Fastenau and G. Y. Robinson

Appl. Phys. Lett. 74, 3758 (1999); http://dx.doi.org/10.1063/1.124171 (3 pages) | Cited 4 times

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Semiconductor alloy heterojunctions, with compositions selected to achieve small band offset energies, were used in distributed Bragg reflector (DBR) structures for the purpose of lowering the vertical series resistance. The heterojunctions were simple abrupt interfaces without composition grading. 40 period mirrors of AlGaInP/Al(Ga)As layer pairs were grown by gas-source molecular beam epitaxy. Mirror reflectance values were found to be greater than 99% at wavelengths near 650 nm. Measured specific resistance values, 2.8×10−4 Ω cm2 for a p-type DBR and 2.6×10−5 Ω cm2 for a n-type DBR, were comparable to or better than (Al)GaAs/Al(Ga)As DBRs employing various graded interface composition designs. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
73.20.At Surface states, band structure, electron density of states
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors

Planar contact geometry for far-infrared germanium lasers

D. R. Chamberlin, E. Bründermann, and E. E. Haller

Appl. Phys. Lett. 74, 3761 (1999); http://dx.doi.org/10.1063/1.124219 (3 pages) | Cited 3 times

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We demonstrate operation of p-Ge far-infrared lasers with a planar contact geometry. The smallest laser crystal with this geometry has a maximum pulse length of 22 μs, which is 10% longer than the pulse length of comparably doped lasers with the traditional contact geometry. Calculations of the electric field distribution show that the fraction of active crystal volume for this new geometry is ∼four times larger than that of traditional geometries. Experiments and calculations reveal that in the planar design, the minimum applied voltage necessary for lasing decreases when the crystal geometry approaches a flat planar structure. This is due to a significant increase of the total electric field caused by the Hall effect. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
72.20.My Galvanomagnetic and other magnetotransport effects

In-plane electro-optic anisotropy of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 thin films grown on (100)-cut LaAlO3

Yalin Lu, Jianjun Zheng, Mark Croning Golomb, Feiling Wang, Hua Jiang, and Jing Zhao

Appl. Phys. Lett. 74, 3764 (1999); http://dx.doi.org/10.1063/1.124172 (3 pages) | Cited 30 times

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Strong electro-optical (EO) anisotropy has been measured in (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 [(1−x)PMN–xPT] single crystalline films epitaxially grown on (100)-cut LaAlO3 substrate, through using an improved dynamic alternating-current ellipsometric null EO detection technique with high accuracy. Large quadratic EO coefficients, which can be as large as 1.38×10−16 (m/V)2 in 0.67PMN–0.33PT film, were obtained in all the used compositions when electric field was applied along {110} directions. The strong EO anisotropy has been explained according to the structural relationship between ferroelectric polarization, input light polarization, and the applied electric field. © 1999 American Institute of Physics.
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78.20.Jq Electro-optical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.66.Nk Insulators
77.22.Ej Polarization and depolarization
42.70.-a Optical materials
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity

Effect of annealing in two-center holographic recording

Ali Adibi, Karsten Buse, and Demetri Psaltis

Appl. Phys. Lett. 74, 3767 (1999); http://dx.doi.org/10.1063/1.124173 (3 pages) | Cited 24 times

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Persistent holograms are recorded with red light in lithium niobate crystals doped with manganese and iron. We find that the oxidation/reduction state of the crystal has a profound impact on the recording and readout performance. The underlying physical processes are investigated and the recording and readout responses are explained and optimized. © 1999 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
61.72.Cc Kinetics of defect formation and annealing
42.70.Ln Holographic recording materials; optical storage media
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials
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Direct current glow discharges in atmospheric air

Robert H. Stark and Karl H. Schoenbach

Appl. Phys. Lett. 74, 3770 (1999); http://dx.doi.org/10.1063/1.124174 (3 pages) | Cited 76 times

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Direct current glow discharges have been operated in atmospheric air by using 100 μm microhollow cathode discharges as plasma cathodes. The glow discharges were operated at currents of up to 22 mA, corresponding to current densities of 3.8 A/cm2 and at average electric fields of 1.2 kV/cm. Electron densities in the glow are in the range from 1012 to 1013 cm−3. Varying the current of the microhollow cathode discharge allows us to control the current in the atmospheric pressure glow discharge. Large volume atmospheric pressure air plasmas can be generated by operating microhollow cathode discharges in parallel. © 1999 American Institute of Physics.
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52.80.Hc Glow; corona
52.25.-b Plasma properties
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Role of surface defect states in visible luminescence from oxidized hydrogenated amorphous Si/hydrogenated amorphous Ge multilayers

Jun Xu, ZhenHong He, Kunji Chen, Xinfan Huang, Duan Feng, Hexiang Han, Zhaoping Wang, and Guohua Li

Appl. Phys. Lett. 74, 3773 (1999); http://dx.doi.org/10.1063/1.124175 (3 pages) | Cited 1 time

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Nanocrystalline Ge embedded in amorphous silicon dioxide matrix was fabricated by oxidizing hydrogenated amorphous Si/hydrogenated amorphous Ge (a-Si:H/a-Ge:H) multilayers. The structures before and after oxidation were systematically investigated. The orange-green light emission was observed at room temperature and the luminescence peak was located at 2.2 eV. The size dependence in the photoluminescence peak energy was not observed and the luminescence intensity was increased gradually with oxidation time. The origin for this visible light emission is discussed. In contrast to the simple quantum effect model, the surface defect states of nanocrystalline Ge are believed to play an important role in radiative recombination process. © 1999 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.66.Jg Amorphous semiconductors; glasses
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.55.Cn Elemental semiconductors
71.55.Jv Disordered structures; amorphous and glassy solids
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors

Structured films of light-emitting silicon nanoparticles produced by cluster beam deposition

Friedrich Huisken, Bernhard Kohn, and Vincent Paillard

Appl. Phys. Lett. 74, 3776 (1999); http://dx.doi.org/10.1063/1.124176 (3 pages) | Cited 28 times

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Crystalline silicon nanoparticles (quantum dots) with diameters around 4 nm are produced via CO2-laser-induced decomposition of SiH4 in a flow reactor and subsequently transferred into a freely propagating cluster beam. Thin structured films are then obtained by shaping the beam with a mask and depositing the nanoclusters at low energy on a sapphire substrate. Upon illumination with ultraviolet radiation, the nanoparticles exhibit strong photoluminescence in the red. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Homeotropic liquid-crystal device with two metastable states

Li-Yi Chen and Shu-Hsia Chen

Appl. Phys. Lett. 74, 3779 (1999); http://dx.doi.org/10.1063/1.124177 (3 pages) | Cited 5 times

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We report a homeotropic liquid-crystal device which has two metastable states when an electric field is applied. The behaviors of these two metastable states are similar to the bistable twist nematic device. We control this device electrically in the rising period to switch it from the homeotropic state toward either the twist or homogeneous state. It not only behaves as a conventional homeotropic cell but also provides another twist structure for further applications. The back-flow effect in the rising period plays an important role in the switching mechanism. The experimental results are described in this letter. © 1999 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Static compression of Ti3SiC2 to 61 GPa

A. Onodera, H. Hirano, T. Yuasa, N. F. Gao, and Y. Miyamoto

Appl. Phys. Lett. 74, 3782 (1999); http://dx.doi.org/10.1063/1.124178 (3 pages) | Cited 50 times

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Synchrotron x-ray diffraction measurements have been made on hexagonal crystal Ti3SiC2 under pressures up to 61 GPa and at room temperature. No phase transition was observed within the pressure range studied. Both the a and c axes exhibited decreases with pressure, accompanied by a decrease in the c/a ratio to about 50 GPa, beyond which the ratio increased. The bulk modulus deduced from the volume-versus-pressure data was 206±6 GPa (with its pressure derivative 4.0±0.3), being close to that of TiC. © 1999 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.66.Fn Inorganic compounds

Self-assembled carbon-induced germanium quantum dots studied by grazing-incidence small-angle x-ray scattering

J. Stangl, V. Holý, P. Mikulík, G. Bauer, I. Kegel, T. H. Metzger, O. G. Schmidt, C. Lange, and K. Eberl

Appl. Phys. Lett. 74, 3785 (1999); http://dx.doi.org/10.1063/1.124179 (3 pages) | Cited 23 times

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We present a structural investigation of buried C-induced Ge quantum dot multilayers grown on (001) Si by molecular-beam epitaxy. Using grazing-incidence small angle x-ray scattering, we determine the shape, the mean radius, height, and dot distance. The dot distribution is isotropic within the (001) interfaces, and no correlation of the dot positions along growth direction was found. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.70.Ck X-ray scattering
68.35.Ct Interface structure and roughness

Gas-phase nanoparticle formation and transport during pulsed laser deposition of Y1Ba2Cu3O7−d

D. B. Geohegan, A. A. Puretzky, and D. J. Rader

Appl. Phys. Lett. 74, 3788 (1999); http://dx.doi.org/10.1063/1.124180 (3 pages) | Cited 22 times

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The gas-phase growth and transport of nanoparticles are characterized at the low background oxygen pressures used for pulsed laser deposition of high-Tc Y1Ba2Cu3O7−d superconducting films. Onset times and pressures for gas-phase nanoparticle formation were determined by intensified charge-coupled device imaging and optical spectroscopy of laser-induced fluorescence from diatomic oxides and Rayleigh scattering from gas-suspended nanoparticles. Nanoparticles are detected for oxygen pressures above 175 mTorr at room temperature, with growth continuing during seconds within the cloud of stopped vapor near the heater surface. Elevated heater temperatures create background density gradients which result in reduced resistance to the initial plume expansion. The temperature gradient also moves nanoparticles away from the heater surface as they grow, effectively limiting the time and spatial confinement necessary for continued growth or aggregation, and inhibiting deposition by thermophoresis. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Gz Optical properties
78.35.+c Brillouin and Rayleigh scattering; other light scattering
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Photoinduced liquid crystal alignment based on a surface relief grating in an assembled cell

Xiang Tong Li, Almeria Natansohn, and Paul Rochon

Appl. Phys. Lett. 74, 3791 (1999); http://dx.doi.org/10.1063/1.124181 (3 pages) | Cited 30 times

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Surface relief gratings have been optically inscribed on azopolymer films on the interior surface of an empty liquid crystal (LC) cell. Uniform LC alignment is observed in the inscribed regions when the cell is filled. Since the microgrooves are on both sides, this may provide a higher degree of order than other techniques. The stability of the relief gratings and the transmittance of the azopolymer films can be further improved by photobleaching. This alignment technique could have useful applications in the in-plane switching LC displays. © 1999 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
68.35.Md Surface thermodynamics, surface energies
42.70.Jk Polymers and organics
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Thermoelectric properties of Tl2SnTe5 and Tl2GeTe5

Jeff W. Sharp, Brian C. Sales, David G. Mandrus, and Bryan C. Chakoumakos

Appl. Phys. Lett. 74, 3794 (1999); http://dx.doi.org/10.1063/1.124182 (3 pages) | Cited 22 times

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We report on the thermoelectric properties of two ternary tellurides with known crystal structures. Both compounds have a very low lattice thermal conductivity. Tl2SnTe5 appears to have a p-type figure of merit about the same as that of Bi2Te3, the best thermoelectric material among binary compounds. We have synthesized mainly polycrystalline samples, but a few small crystals have been grown and used for electrical measurements. Prospects for further improvement of these materials are discussed. © 1999 American Institute of Physics.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects

Light-induced electron spin resonance in amorphous hydrogenated germanium

F. C. Marques, M. M. de Lima, and P. C. Taylor

Appl. Phys. Lett. 74, 3797 (1999); http://dx.doi.org/10.1063/1.124183 (3 pages) | Cited 3 times

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We report the observation of light-induced electron spin resonance (LESR) in amorphous hydrogenated germanium. Two new lines with zero crossings near g = 2.01 and g = 2.03 were detected and ascribed to electrons and holes in the conduction- and valence-band-tail states, respectively. The ratio between the LESR spin densities of both lines is approximately one, suggesting the absence of spin pairing, charge defect creation, or LESR of dangling bonds. The growth and decay spectra exhibit dispersive behavior with a dispersion parameter ∼0.5. The decay spectrum is best fit assuming bimolecular recombination. The LESR spin density depends weakly on the photogeneration rate as a sublinear power law. © 1999 American Institute of Physics.
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76.30.Mi Color centers and other defects
71.55.Jv Disordered structures; amorphous and glassy solids
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Surface loss probabilities of the dominant neutral precursors for film growth in methane and acetylene discharges

C. Hopf, K. Letourneur, W. Jacob, T. Schwarz-Selinger, and A. von Keudell

Appl. Phys. Lett. 74, 3800 (1999); http://dx.doi.org/10.1063/1.124184 (3 pages) | Cited 33 times

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The surface loss probabilities of the dominant neutral growth species emanating from methane and acetylene discharges are investigated by depositing thin films inside a cavity. The walls of this cavity are made from silicon substrates. Particles from the plasma can enter the cavity through a slit. The surface loss probability is determined by analysis of the deposition profile inside the cavity. This surface loss probability corresponds to the sum of the probability for effective sticking on the surface and the probability for the formation of a nonreactive volatile product via surface reactions. In a methane discharge the surface loss probability is ∼ 0.65±0.15 and in an acetylene discharge ∼ 0.92±0.05, respectively. The dominant contribution in the neutral radical flux emanating from a methane discharge towards the surface consists of CH3 radicals, as known from experiments using mass spectrometry. Furthermore, it is known from literature that the upper limit for the reaction probability for CH3 is in the range of 10−2. This leads us to the conclusion that the CH3 radical is not the dominant neutral growth precursor in a methane discharge. This result refutes the widely accepted picture that CH3 radicals are the dominant neutral growth precursor in a-C:H growth from methane. From a comparison of the composition of the neutral flux towards the surface from methane and acetylene discharges, we conclude that in both cases C2Hy species are the dominant neutral precursors for film growth. © 1999 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Elastic strain of freely suspended single-wall carbon nanotube ropes

D. A. Walters, L. M. Ericson, M. J. Casavant, J. Liu, D. T. Colbert, K. A. Smith, and R. E. Smalley

Appl. Phys. Lett. 74, 3803 (1999); http://dx.doi.org/10.1063/1.124185 (3 pages) | Cited 220 times

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We have induced large elastic strains in ropes of single-wall carbon nanotubes, using an atomic force microscope in lateral force mode. Freely suspended ropes were observed to deform as elastic strings with tension proportional to elongation. Ropes were elastically deformed over >10 cycles without showing signs of plastic deformation. The maximum strain observed, 5.8±0.9%, gives a lower bound of 45±7 GPa for the tensile strength (specifically, yield stress) of single-wall nanotube ropes. © 1999 American Institute of Physics.
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62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Soft x-ray absorption of a buried SmCo film utilizing substrate fluorescence detection

I. Coulthard, J. W. Freeland, R. Winarski, D. L. Ederer, J. S. Jiang, A. Inomata, S. D. Bader, and T. A. Callcott

Appl. Phys. Lett. 74, 3806 (1999); http://dx.doi.org/10.1063/1.124186 (3 pages) | Cited 1 time

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Oxygen K-shell x-ray fluorescence was monitored from the MgO substrate of a metallic heterostructure system containing a buried SmCo permanent magnet layer. This fluorescence was utilized as a detector to record transmission yield spectra for the SmCo film at both the Co–L3,2 and Sm–M5,4 absorption edges. Ordinarily, traditional transmission yield spectroscopy in the soft x-ray regime is impossible to perform with films on single-crystal substrates. The measured intensity ratios agree with simulations to confirm the thickness information. The potential and limitations of this technique are discussed in comparison to standard total electron and fluorescence yield techniques and magnetic circular dichroism. © 1999 American Institute of Physics.
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78.70.Dm X-ray absorption spectra
75.50.Ww Permanent magnets
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Light emission during fracture of a Zr–Ti–Ni–Cu–Be bulk metallic glass

C. J. Gilbert, J. W. Ager, V. Schroeder, R. O. Ritchie, J. P. Lloyd, and J. R. Graham

Appl. Phys. Lett. 74, 3809 (1999); http://dx.doi.org/10.1063/1.124187 (3 pages) | Cited 48 times

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A light emission phenomenon observed during dynamic fracture of a bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10Be22.5 (at. %), has been investigated using Charpy V-notch impact specimens. Unlike more conventional crystalline metals, these Zr-based amorphous alloys emit intense flashes of visible light when ruptured. The mechanisms for this surprising behavior are unknown and the phenomenon remains uncharacterized. Here we report spectroscopic measurements of the light emitted from specimens fractured in both room air and nitrogen gas. Spectra acquired from specimens ruptured in air exhibited a single broad peak, which could be fit to a blackbody temperature of ∼3175 K. Emission from specimens fractured in nitrogen, however, was at least four orders of magnitude less intense. The spectrum was shifted to the red with an effective blackbody temperature of ∼1400 K. Fracture surfaces of specimens ruptured in both air and nitrogen exhibited local melting, providing further evidence of intense heating during fracture. Based on these observations we argue that the intense light emission in air is associated with pyrolysis of fresh material exposed during rupture. © 1999 American Institute of Physics.
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78.60.-b Other luminescence and radiative recombination
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Spatial distribution of radiation-induced defects in p+-n InGaP solar cells

M. J. Romero, D. Araújo, R. García, R. J. Walters, G. P. Summers, and S. R. Messenger

Appl. Phys. Lett. 74, 3812 (1999); http://dx.doi.org/10.1063/1.124188 (3 pages) | Cited 3 times

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The spatial distribution of radiation-induced, radiative recombination centers in single-junction p+-n InGaP solar cells irradiated by 1 MeV electrons or 3 MeV protons has been determined from cathodoluminescence (CL) spectra. The energy levels of the radiation-induced, nonradiative recombination centers were determined from the temperature dependence of the CL intensity. © 1999 American Institute of Physics.
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84.60.Jt Photoelectric conversion
61.82.Fk Semiconductors
71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
61.80.Jh Ion radiation effects
61.80.Fe Electron and positron radiation effects

Near-ultraviolet and near-infrared electroluminescence from an indium–tin–oxide film/native Si oxide/p-Si structure

Y. Q. Wang, T. P. Zhao, J. Liu, and G. G. Qin

Appl. Phys. Lett. 74, 3815 (1999); http://dx.doi.org/10.1063/1.124189 (3 pages) | Cited 14 times

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We have deposited indium–tin–oxide (ITO) films on p-Si (100) substrates with native Si oxide layers on their surfaces using the electron beam depositing technique. After the ITO/native Si oxide/p-Si structure was annealed in a N2 ambient, electroluminescence spectra with two peaks at near-ultraviolet (∼360 nm) and near-infrared (∼820 nm) have been measured under a forward bias of 6 V or larger. The experimental results have been interpreted tentatively using the tunneling-luminescence center process. It is considered that the two electroluminescence peaks originate from two groups of luminescence centers in the native Si oxide layers. The luminescence centers responsible for the near-ultraviolet peak have been discussed. © 1999 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Li Other semiconductors
78.66.Nk Insulators
73.40.Ty Semiconductor-insulator-semiconductor structures
61.72.Cc Kinetics of defect formation and annealing
73.40.Gk Tunneling

Stress relaxation by surface rippling and dislocation generation in mismatched channels of InGaAs/InAlAs/InP high-electron-mobility transistors

F. Peiró, A. Cornet, M. Beck, and M. A. Py

Appl. Phys. Lett. 74, 3818 (1999); http://dx.doi.org/10.1063/1.124190 (3 pages) | Cited 4 times

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We have investigated InGaAs strained channels of high-electron-mobility transistor heterostructures with In compositions of 70% and 80% and channel thicknesses covering the range of 3–14 nm. Transmission electron microscopy characterization has revealed the existence of two regimes of strain relaxation in these strained InGaAs channels: (i) an anisotropic rippling of the channel surface at low mismatch and (ii) dislocation generation as the layer thickness and mismatch increase. The correlation of structural features with electrical measurements has provided evidence of a significant reduction of the Hall mobility values measured across the rippling of the InGaAs well. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.35.Ct Interface structure and roughness
68.35.Gy Mechanical properties; surface strains

Optical properties of a high-quality insulating GaN epilayer

K. C. Zeng, J. Y. Lin, H. X. Jiang, and Wei Yang

Appl. Phys. Lett. 74, 3821 (1999); http://dx.doi.org/10.1063/1.124191 (3 pages) | Cited 10 times

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Picosecond time-resolved photoluminescence (PL) spectroscopy has been used to investigate the optical properties of an insulating GaN epilayer grown by metalorganic chemical vapor deposition on a sapphire substrate. Two emission lines at 3.503 and 3.512 eV in the continuous wave (cw) PL spectra observed at 10 K under a low excitation intensity ( ∼ 23 W/cm2) were identified as the band-to-band transitions involving the A and B valence bands, respectively. A third emission line at 3.491 eV was identified as a band-to-impurity transition involving a shallow donor. The PL decay behavior can be well understood with a model taking into account both the free carriers and impurities. The effective recombination lifetime of the band-to-band transition in GaN was found to be about 3.7 ns. Possible mechanisms for the band-to-band transition being dominant in this high quality insulating GaN epilayer have also been discussed. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
78.47.-p Spectroscopy of solid state dynamics
71.55.Eq III-V semiconductors

Germanium dioxide whiskers synthesized by laser ablation

Y. H. Tang, Y. F. Zhang, N. Wang, I. Bello, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 74, 3824 (1999); http://dx.doi.org/10.1063/1.124192 (3 pages) | Cited 29 times

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We obtained germanium dioxide (GeO2) whiskers in bulk quantity by ablating a germanium target at 820 °C with a pulsed KrF excimer laser in an argon atmosphere. Most of the GeO2 whiskers were smooth and straight with hexagonal or triangular, or quadrilateral cross sections while some of them had a bamboo-shoot-shaped form. Results of scanning electron microscopy, transmission electron microscopy, and x-ray diffraction showed that the whiskers are hexagonal crystalline GeO2. © 1999 American Institute of Physics.  
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.15.Fg Pulsed laser ablation deposition

Giant electric fields in unstrained GaN single quantum wells

R. Langer, J. Simon, V. Ortiz, N. T. Pelekanos, A. Barski, R. André, and M. Godlewski

Appl. Phys. Lett. 74, 3827 (1999); http://dx.doi.org/10.1063/1.124193 (3 pages) | Cited 79 times

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We demonstrate that, even in unstrained GaN quantum wells with AlGaN barriers, there exist giant electric fields as high as 1.5 MV/cm. These fields, resulting from the interplay of the piezoelectric and spontaneous polarizations in the well and barrier layers due to Fermi level alignment, induce large redshifts of the photoluminescence energy position and dramatically increase the carrier lifetime as the quantum well thickness increases. © 1999 American Institute of Physics.
Show PACS
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.65.-j Piezoelectricity and electromechanical effects
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