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20 Apr 1998

Volume 72, Issue 16, pp. 1939-2058

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Continuous-wave operation of InGaN/GaN/AlGaN-based laser diodes grown on GaN substrates

Shuji Nakamura, Masayuki Senoh, Shin-ichi Nagahama, Naruhito Iwasa, Takao Yamada, Toshio Matsushita, Hiroyuki Kiyoku, Yasunobu Sugimoto, Tokuya Kozaki, Hitoshi Umemoto, Masahiko Sano, and Kazuyuki Chocho

Appl. Phys. Lett. 72, 2014 (1998); http://dx.doi.org/10.1063/1.121250 (3 pages) | Cited 167 times

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InGaN multi-quantum-well-structure laser diodes (LDs) grown on GaN substrates were demonstrated. The LDs showed a small thermal resistance of 30 °C/W and a lifetime longer than 780 h despite a large threshold current density of 7 kA/cm2. In contrast, the LDs grown on a sapphire substrate exhibited a high thermal resistance of 60 °C/W and a short lifetime of 200 h under room-temperature continuous-wave operation. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors

Electrical properties of semiconductive Nb-doped BaTiO3 thin films prepared by metal–organic chemical-vapor deposition

Daisuke Nagano, Hiroshi Funakubo, Kazuo Shinozaki, and Nobuyasu Mizutani

Appl. Phys. Lett. 72, 2017 (1998); http://dx.doi.org/10.1063/1.121251 (3 pages) | Cited 12 times

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Epitaxially grown semiconductive Nb-doped BaTiO3 thin films with low electrical resistivity similar to that of the bulk single crystal were prepared by metal–organic chemical-vapor deposition. Thin films with 1.5–7.5 at. % Nb content showed n-type semiconductor character. The films with 5.7 at. % Nb content showed the lowest resistivity, 2.8×10−2 Ω cm. This value is three orders of magnitude lower than those reported for sintered of Nb-doped BaTiO3, and similar to that of Nb-doped BaTiO3 single crystals. © 1998 American Institute of Physics.
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72.80.Ga Transition-metal compounds
73.61.Le Other inorganic semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Dn Low-field transport and mobility; piezoresistance
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
72.20.Fr Low-field transport and mobility; piezoresistance

Far-infrared photoconductivity in self-organized InAs quantum dots

J. Phillips, K. Kamath, and P. Bhattacharya

Appl. Phys. Lett. 72, 2020 (1998); http://dx.doi.org/10.1063/1.121252 (3 pages) | Cited 111 times

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We report far-infrared photoconductivity in self-organized InAs/GaAs quantum dots grown by molecular beam epitaxy. Through use of a Fourier transform infrared spectrometer, a photoconductivity signal peaked at 17 μm is observed from a n–i–n detector structure with doped InAs quantum dots in the intrinsic region. Comparison of photoluminescence and band-to-band photocurrent absorption spectra suggests the far-infrared response is due to intersubband transitions in the quantum dots. © 1998 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
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
78.30.Fs III-V and II-VI semiconductors

Hg1−xCdxI2/CdTe heterostructures for nuclear radiation detectors: Effect of epitaxial growth on substrate properties

N. V. Sochinskii, V. Muñoz, J. M. Perez, J. Cárabe, and A. Morales

Appl. Phys. Lett. 72, 2023 (1998); http://dx.doi.org/10.1063/1.121253 (3 pages) | Cited 4 times

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We demonstrate the possibility to fabricate nuclear radiation detectors operating at room temperature from CdTe substrates affected by the vapor phase epitaxy (VPE) growth of Hg1−xCdxI2 layers. The VPE layers with the thickness 10–30 μm were grown using an α-HgI2 polycrystalline source at 220 °C and time in the range of 30–100 h. The as-grown heterostructures were chemically etched to remove the epilayers, and Au–CdTe–Au detectors were made. The substrates were characterized by synchrotron x-ray topography before and after the VPE growth, and the current–voltage (I–V) and spectroscopic measurements of the detectors were carried out. The effect of the VPE growth on the substrates and detectors has been studied and on the basis of this it has been possible to fabricate γ-ray detectors with Ohmic I–V characteristic and good spectral response. © 1998 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
29.40.Wk Solid-state detectors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.40.Sx Metal-semiconductor-metal structures
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Comparison of the annealing behavior of high-dose nitrogen-, aluminum-, and boron-implanted 4H–SiC

S. Seshadri, G. W. Eldridge, and A. K. Agarwal

Appl. Phys. Lett. 72, 2026 (1998); http://dx.doi.org/10.1063/1.121681 (3 pages) | Cited 21 times

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Room temperature free carrier concentrations exceeding 1×1018 cm−1 have been achieved with 1000 °C implants into 4H–SiC using N and Al (1×1017 cm−3 using B). A decrease in resistivity is observed for annealing temperatures above ∼ 1300, ∼ 1500, and ∼ 1750 °C for N, Al, and B, respectively. Rutherford backscattering spectroscopy measurements indicate almost complete recrystallization for N-implanted samples and partial recrystallization on the silicon, but not the carbon, sublattice for B- and Al-implanted samples. An implant and species related step formation is also observed. Only boron is observed to diffuse appreciably. A crystal stoichiometry and Fermi level dependent model is proposed to explain the activation results. © 1998 American Institute of Physics.
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81.05.Hd Other semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.72.up Other materials
61.66.Bi Elemental solids
61.66.Dk Alloys
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A design of planar multi-turn flux transformers for radio frequency SQUID magnetometers

Y. Zhang, H. R. Yi, J. Schubert, W. Zander, M. Banzet, and A. I. Braginski

Appl. Phys. Lett. 72, 2029 (1998); http://dx.doi.org/10.1063/1.121254 (3 pages) | Cited 5 times

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We propose a design for planar multi-turn flux transformer for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. This transformer is integrated with a coplanar resonator, e.g., on a 1 cm2 LaAlO3 substrate. Its pickup loop is connected with two input coils, separate for dc (low-frequency) and rf currents. A double-hole washer SQUID is coupled to these coils in a flip-chip configuration to form a magnetometer. The separation of rf and dc current paths in the transformer made it possible to demonstrate the rf SQUID magnetometer operation. © 1998 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements

Planar thin film YBa2Cu3O7−δ Josephson junctions via nanolithography and ion damage

A. S. Katz, A. G. Sun, S. I. Woods, and R. C. Dynes

Appl. Phys. Lett. 72, 2032 (1998); http://dx.doi.org/10.1063/1.121255 (3 pages) | Cited 24 times

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We have developed a process to fabricate planar high-Tc Josephson junctions using nanolithography and a 200 keV ion implanter. Conduction occurs in the ab plane and is interface free. We can systematically tune devices to operate at temperatures between 1 K and the Tc of the undamaged superconducting material by varying the length of the weak link and by changing the amount of ion damage. All of the devices showed clear dc and ac Josephson effects. Measurement of R(T) and Ic(T) of the weak links revealed trends which were consistent with a proximity effect. © 1998 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.80.Jh Ion radiation effects

Highly stable surfaces of Nd1Ba2Cu3Oy single crystals

Wu Ting, N. Koshizuka, and S. Tanaka

Appl. Phys. Lett. 72, 2035 (1998); http://dx.doi.org/10.1063/1.121256 (3 pages) | Cited 7 times

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Single crystals of Nd1Ba2Cu3Oy (Nd123) high-temperature superconductors have been studied using an ultrahigh vacuum scanning tunneling microscope/spectroscopy system at room temperature. A square lattice with average lattice spacings of 4×4 Å2 has been observed on the surfaces of the single crystals without any surface protections or treatments. The as-prepared surfaces are found to be terminated by the CuO chain layer. Several surface defect structures presumably caused by the oxygen depletion are revealed. Among them, an one dimensional structural modulation with period of 1.5 nm along b axis is seen, which is suggested to be created by the ordering of the oxygen vacancies. The surfaces of Nd123 single crystals are proved to be highly clean and stable in air. Our results indicate that Nd123 single crystals are good materials for surface sensitive scientific researches and device applications. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
61.66.Bi Elemental solids
61.66.Dk Alloys
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
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Magnetoresistance of artificial La0.7Sr0.3MnO3 grain boundaries as a function of misorientation angle

S. P. Isaac, N. D. Mathur, J. E. Evetts, and M. G. Blamire

Appl. Phys. Lett. 72, 2038 (1998); http://dx.doi.org/10.1063/1.121257 (3 pages) | Cited 67 times

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The resistance of polycrystalline doped LaMnO3 materials has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries we have grown epitaxial La0.7Sr0.3MnO3 films on a series of bicrystal substrates with different misorientation angles and patterned the films into a Wheatstone bridge geometry. We show that the grain boundary resistance and its magnetic field dependence vary strongly with the misorientation angle. The temperature dependence of the grain boundary resistance is also presented. We have obtained resistance changes of over 3% in fields of 2 mT at 300 K. © 1998 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.47.De Giant magnetoresistance

Phase transitions in planar magnetic nanostructures

R. P. Cowburn and M. E. Welland

Appl. Phys. Lett. 72, 2041 (1998); http://dx.doi.org/10.1063/1.121258 (3 pages) | Cited 60 times

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Using numerical micromagnetics we have studied the ground state magnetization distribution of square planar ferromagnetic elements (“nanostructures”). As the element size is reduced from 250 to 2 nm at constant thickness (2–35 nm), we find that the magnetization distribution undergoes up to three phase transitions involving as many as three different near single domain states. One of these phase transitions is analogous to the reorientation phase transition observed in continuous ultrathin magnetic films. © 1998 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.60.Ch Domain walls and domain structure

Magnetoelastic properties of epitaxial holmium and erbium thin films

M. Ciria, J. I. Arnaudas, A. del Moral, M. R. Wells, and R. C. C. Ward

Appl. Phys. Lett. 72, 2044 (1998); http://dx.doi.org/10.1063/1.121259 (3 pages) | Cited 4 times

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The magnetoelastic (MEL) stresses of single crystal Ho and Er thin films are measured at low temperatures and in applied magnetic fields up to 12 T by means of a capacitive cantilever technique, to determine the irreducible second-order basal plane MEL stress Bγ,2. For Ho, the data are well fit by the Callen and Callen law, giving Bγ,2=0.29 GPa at 0 K and 12 T, slightly larger than the bulk value, which suggest a negligible effect of the clamping on Bγ,2. For Er, the lack of saturation prevents the determination of the single-ion contribution to Bγ,2 at 0 K. Nevertheless, its sign, which is negative, agrees with the theoretical crystal field prediction. © 1998 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction

Mössbauer and magnetic study of substituted magnetites

M. Sorescu, D. Mihaila-Tarabasanu, and L. Diamandescu

Appl. Phys. Lett. 72, 2047 (1998); http://dx.doi.org/10.1063/1.121260 (3 pages) | Cited 20 times

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Co, Ni, Mn, Cr, and Cu substituted magnetites were prepared by the hydrothermal method at 300 °C, with concentrations ranging from 8.2% to 12.5%. Transmission electron microscopy determined the average particle diameter 〈Φ〉 to be in the hundred of nm range and the morphological modifications induced by the various substitutions employed. Hysteresis loop measurements were performed to determine the coercive field Hc, and saturation magnetic moment ms. While Hc decreased with increasing 〈Φ〉, the particle shape was found to play an important role in explaining the dependence of ms on 〈Φ〉. Transmission Mössbauer spectroscopy was used to determine the site preference of the substitutions and their effect on the hyperfine magnetic fields. The room-temperature Mössbauer spectra were analyzed assuming a random distribution of substitutents using the binomial distribution from the ionic crystal point of view. Superparamagnetic particles were observed at room temperature in the case of Cu and Cr substituted magnetites. © 1998 American Institute of Physics.
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75.30.Hx Magnetic impurity interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials

Spin dependent electron absorption in Fe(001)-p(1×1)O: A new candidate for a stable and efficient electron polarization analyzer

Riccardo Bertacco, Michele Merano, and Franco Ciccacci

Appl. Phys. Lett. 72, 2050 (1998); http://dx.doi.org/10.1063/1.121261 (3 pages) | Cited 30 times

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The low energy electron absorption by a p(1×1) ordered oxygen overlayer on magnetized Fe(001) depends on the spin polarization of the primary beam. The peak value of the spin asymmetry is 12.5% at 6 eV electron kinetic energy, where the percentage absorption is 65%. The presence of the surface oxide prevents the system from contamination, so that an almost negligible asymmetry deterioration is observed after prolonged operation in vacuum. After exposure to atmosphere followed by heat-cleaning a peak value still larger than 7% is achieved. These results suggest spin dependent current absorption from Fe(001)-p(1×1)O as a very promising candidate for an efficient and extremely stable electron polarization analyzer. © 1998 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
07.60.Fs Polarimeters and ellipsometers
61.80.Fe Electron and positron radiation effects
81.65.Mq Oxidation

Effect of magnetic field on the superparamagnetic relaxation in granular Co-Ag samples

Y. D. Zhang, J. I. Budnick, W. A. Hines, C. L. Chien, and J. Q. Xiao

Appl. Phys. Lett. 72, 2053 (1998); http://dx.doi.org/10.1063/1.121262 (3 pages) | Cited 22 times

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In order to study the effect of applied magnetic field on the superparamagnetic relaxation behavior of small Co particles, magnetization measurements were carried out on as-prepared and annealed granular samples of Co20Ag80 and Co25Ag75. Values of the superparamagnetic blocking temperature TB− were obtained from the characteristic peak in the zero-field-cooled magnetization. Consistent with existing models, it was found that the initial decrease of TB− with applied magnetic field is quadratic. An estimate of the magnetic anisotropy “energy density” Ku yielded a value which is two orders of magnitude greater than the value for bulk cobalt. The results reported here underscore the importance of considering the effect of superparamagnetic relaxation on the performance of nanostructured magnetic materials. © 1998 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
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Effect of Ti substitution on the thermoelectric properties of the pentatelluride materials M1−xTixTe5 (M = Hf, Zr)

R. T. Littleton, Terry M. Tritt, C. R. Feger, J. Kolis, M. L. Wilson, M. Marone, J. Payne, D. Verebeli, and F. Levy

Appl. Phys. Lett. 72, 2056 (1998); http://dx.doi.org/10.1063/1.121406 (3 pages) | Cited 17 times

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The thermoelectric properties (resistivity and thermopower) of single crystals of the low dimensional pentatelluride materials, HfTe5  and ZrTe5, have been measured as a function of temperature from 10 K<T<320 K. The effect of small amounts of Ti substitutional doping (M1−xTixTe5, where M = Hf, Zr) on the thermoelectric properties is reported here. A resistive transition occurs in the pentatellurides, as evidenced by a peak in the resistivity, TP ≈ 80 K for HfTe5 and TP ≈ 145 K for ZrTe5. Both parent materials exhibit a large positive (p-type) thermopower near room temperature which undergoes a change to negative (n-type) below the peak temperature. The thermal conductivity is relatively low (≈5 W/m K) for the MTe5 materials. The Ti substitution affects the electronic properties strongly, producing a substantial shift in the peak temperature while the large values of thermopower remain essentially unaffected. These results warrant further investigation of these materials as candidates for low temperature thermoelectric applications. © 1998 American Institute of Physics.
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72.80.Ga Transition-metal compounds
72.20.Pa Thermoelectric and thermomagnetic effects
72.60.+g Mixed conductivity and conductivity transitions
72.20.Fr Low-field transport and mobility; piezoresistance
61.66.Bi Elemental solids
61.66.Dk Alloys
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
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