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Applied Physics Letters

Issue 8 • Date Feb 2001

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Displaying Results 1 - 25 of 51
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Low dark current quantum-dot infrared photodetectors with an AlGaAs current blocking layer

    Page(s): 1023 - 1025
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    Low dark current InAs/GaAs quantum-dot infrared photodetectors (QDIPs) are demonstrated. The dark current is reduced by over three orders of magnitude by using a thin AlGaAs current blocking layer. This thin AlGaAs layer reduces the dark current much more than the response signal. The responsivity at 0.5 V is 0.08 A/W with a peak detection wavelength at 6.5μm. The corresponding detectivity is 2.5×109cm Hz1/2/W1/2, which is the highest detectivity reported for a QDIP at 77 K. © 2001 American Institute of Physics. View full abstract»

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  • Injection-seeded terahertz-wave parametric oscillator

    Page(s): 1026 - 1028
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    The narrow linewidth operation of a THz-wave parametric oscillator was achieved through the use of narrow linewidth laser injection. THz-wave parametric oscillation, generated by a LiNbO3 crystal pumped with a single longitudinal mode Q-switched Nd:YAG laser, was injection seeded with a continuous-wave Yb:fiber laser. The measured THz-wave linewidth was 200 MHz, which corresponded to the measurement resolution limit. © 2001 American Institute of Physics. View full abstract»

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  • InAs/AlSb quantum-cascade light-emitting devices in the 3–5 μm wavelength region

    Page(s): 1029 - 1031
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    Midinfrared (3.7–5.3 μm) electroluminescent devices based on a quantum-cascade (QC) design have been demonstrated using InAs/AlSb heterostructures, grown on GaSb substrates. The very high conduction band discontinuity (≫2 eV) of this material system allows the design of QC devices at very short wavelengths. Well-resolved luminescence peaks were observed up to 300 K, with a full-width-at-half-maximum to peak wavelength ratio (Δλ/λ) of the order of 8%. The emission wavelengths are in good agreement with the results of our model. The emitted optical power is lower than that predicted, due to a nonoptimized electron injection into the active region. © 2001 American Institute of Physics. View full abstract»

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  • Photons confined in hollow microspheres

    Page(s): 1032 - 1034
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    Incorporation of CdSe quantum dots into a thin (≪1 μm) surface shell of polymer microspheres (R∼2–4 μm) is achieved. The room-temperature emission spectra of single, hollow microcavities show several, spectrally well-separated cavity modes in the red-orange spectral range which have been assigned to high-Q whispering gallery modes (WGM) with radial quantum number n=1 and high angular quantum number l. An enhancement of the cavity finesse Q by a factor of about 10 with respect to CdSe-doped bulk polymer microspheres is found. © 2001 American Institute of Physics. View full abstract»

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  • Wide-bandwidth high-frequency electro-optic modulator based on periodically poled LiNbO3

    Page(s): 1035 - 1037
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    We propose a high-frequency traveling-wave integrated electro-optic modulator based on a periodically poled LiNbO3. The traveling velocity of the optical wave and the electrical wave velocity in the waveguide can be quasimatched due to the periodic structure. Using this design, a modulation frequency of several hundred GHz can be realized. Wide-bandwidth modulation is also achievable by employing an aperiodic domain grating. © 2001 American Institute of Physics. View full abstract»

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  • Holographic encoding of fine-pitched micrograting structures in amorphous SiO2 thin films on silicon by a single femtosecond laser pulse

    Page(s): 1038 - 1040
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    Fine-pitched micrograting structures were holographically encoded in amorphous (a-) SiO2 thin films on silicon wafers by colliding a pair of focused pulses split from a single, mode-locked Ti: sapphire, femtosecond laser. A method enhancing the third-harmonic generation resulting from the nonlinearity of air adjusted the optical paths of the two pulses. Surface-relief-type gratings were formed on SiO2 glasses due to laser ablation when the laser power exceeded more than 0.3 mJ/pulse, while shallow grating structures were imprinted on a-SiO2 thin films by volume compaction (∼3%) when the irradiation power was reduced to ∼50 μJ/pulse. The postirradiation deepening of the valley of the grating structure was possible with chemical etching. The minimal spacing of 430 nm was encoded using the 800 nm laser. © 2001 American Institute of Physics. View full abstract»

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  • Terahertz optical pulse generation with a simple encoding scheme using spatial slicing technique

    Page(s): 1041 - 1043
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    We propose and experimentally demonstrate a spatial slicing technique for the generation and encoding of a terahertz optical pulse train. The configuration consists simply of a group of optical delay lines arranged in a two-dimensional array. Optical pulse trains at repetition rates of 0.6 and 1.0 THz are achieved. With the use of spatial masks, different output signals can also be produced. The spatial slicing technique provides a feasibility to switch off selected optical pulses in a terahertz pulse train using low-speed switches. © 2001 American Institute of Physics. View full abstract»

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  • Fabrication of GaP/Al–oxide distributed Bragg reflectors for the visible spectrum

    Page(s): 1044 - 1046
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    Using very-low temperature (VLT) molecular-beam epitaxy (MBE), polycrystalline GaP/Al–oxide distributed Bragg reflectors (DBRs) have been fabricated. The use of high-energy band gap materials, such as GaP, allows for applications in the visible spectrum with minimal absorption of photons in the DBR. Through the use of VLT-MBE and control of the group-V overpressure, the microstructure can be controlled, resulting in either amorphous or polycrystalline material. Due to the nature of the amorphous material, the requirement of lattice matching is relaxed with no adverse effects to the underlying single crystal material. Two DBRs were fabricated, one reflecting at a wavelength of 550 nm and the other 480 nm. Using six pairs of polycrystalline GaP/Al–oxide, a reflectivity of ∼95% was achieved indicating a high-quality DBR suitable for device use. © 2001 American Institute of Physics. View full abstract»

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  • Temperature invariant lasing and gain spectra in self-assembled GaInAs quantum wire Fabry–Perot lasers

    Page(s): 1047 - 1049
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    GaInAs quantum wire (QWR) heterostructures have been grown by molecular beam epitaxy using the strain-induced lateral-layer ordering (SILO) process. Broad-area Fabry–Perot QWR lasers have been fabricated from this material. The lasing wavelength from the QWR laser shifts at a rate of 0.9 Å/°C between 77 and 300 K compared to 4.6 Å/°C for a quantum well laser control sample. Furthermore, the gain spectra of the QWR laser are derived from the amplified spontaneous emission spectra at 77 and 300 K using the Hakki–Paoli method. The gain peak is also stabilized against temperature changes indicating that temperature stable lasing behavior seen in SILO grown GaInAs QWR Fabry–Perot laser diodes is due to a temperature stable band gap. © 2001 American Institute of Physics. View full abstract»

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  • Transparent conducting Zr-doped In2O3 thin films for organic light-emitting diodes

    Page(s): 1050 - 1052
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    Zirconium-doped indium oxide (ZIO) thin films (∼2000 Å thick) have been deposited by pulsed-laser deposition on glass substrates without a postdeposition anneal. The structural, electrical and optical properties of these films have been investigated as a function of substrate temperature and oxygen partial pressure during deposition. Films were deposited at substrate temperatures ranging from 25 °C to 400 °C in O2 partial pressures ranging from 0.1 to 50 mTorr. The films (∼2000 Å thick) deposited at 200 °C in 25 mTorr of oxygen show electrical resistivities as low as 2.5×10-4 Ω cm, an average visible transmittance of 89%, and an optical band gap of 4.1 eV. The ZIO films were used as a transparent anode contact in organic light emitting diodes and the device performance was studied. The external quantum efficiency measured from these devices was about 0.9% at a current density of 100 A/m2. © 2001 American Institute of Physics. View full abstract»

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  • Transient response of a bilayer organic electroluminescent diode: Experimental and theoretical study of electroluminescence onset

    Page(s): 1053 - 1055
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    The experimental transient electroluminescence response of a bilayer organic light-emitting diode reported here shows an initial overshoot when sufficient direct current bias is superimposed to pulse excitation. Using a theoretical model giving the kinetic equations which govern the time evolution of electrical fields, currents and charge densities in the device, we calculate transient response of light emission. The results show a good agreement with experiments and evidence the charge carriers accumulation occurring in the region of organic–organic interface due to unipolar injection. Application of periodic excitation indicates that a characteristic time of 300 ms is needed to recover the initial electrical equilibrium state. © 2001 American Institute of Physics. View full abstract»

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  • X-ray determination of vertical ordering of InAs quantum dots in InAs/GaAs multilayers

    Page(s): 1056 - 1058
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    The degree of vertical alignment of InAs quantum dots in InAs/GaAs(001) multilayers was studied using grazing incidence x-ray scattering. We show that it is necessary to access one of the weak (200) x-ray reflections to observe the modulation of the GaAs lattice periodicity produced by the stacking of the InAs dots. The degree of alignment of the dots was assessed by fitting the x-ray diffuse scattering profiles near a GaAs (200) reciprocal lattice point. By using a model of gaussian lateral displacement of the dots, we show that we can determine the average value of the mistake in stacking positions of the islands from one bilayer to the next. © 2001 American Institute of Physics. View full abstract»

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  • Excited-state quenching of a highly luminescent conjugated polymer

    Page(s): 1059 - 1061
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    The optical properties of a luminescent polymer, poly[1,4-phenylene-1,2-di(phenoxyphenyl) vinylene], have been investigated. Its photoluminescence yield increases unusually in the solid-state over solution, 52%–6% respectively. Investigations into the stimulated emission properties of this material were carried out but no amplified spontaneous emission was observed. To investigate the presence of excited-state absorption features, the photoinduced absorption spectrum was measured. An observed polaron absorption band, from 1.5 to 2.25 eV, overlaps the emission spectra and therefore quenches stimulated emission. This highlights the need to consider the effects of excited-state absorption on the emission when synthesizing new materials. © 2001 American Institute of Physics. View full abstract»

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  • Time-resolved spectroscopy of strained GaN/AlN/6H–SiC heterostructures grown by metalorganic chemical vapor deposition

    Page(s): 1062 - 1064
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    Temperature-dependent time-resolved photoluminescence measurements were performed on GaN film/AlN buffer/6H–SiC substrate heterostructures grown by metalorganic chemical vapor deposition. The overlying GaN layers were under tension, as estimated from the free A exciton (FEA) position. The recombination lifetimes were determined for the FEA and for the neutral-donor-bound exciton (D0X). We observed that the recombination lifetime for the FEA has the same value of 40–50 ps in all the layers, whereas the recombination time for the D0X varies for different samples. We observed that the recombination lifetimes for D0X have a clear dependence on the position of FEA, i.e., the recombination lifetime increases with decreasing strain in the layers. We discuss the results in term of the hole states involved in the donor-bound exciton recombination. © 2001 American Institute of Physics. View full abstract»

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  • Room-temperature random telegraph noise in luminescence from macroscopic InGaN clusters

    Page(s): 1065 - 1067
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    We report on photoluminescence properties of individual macroscopically sized InGaN clusters that were formed in InGaN multiple quantum wells. Phase separation in InGaN results in the formation of clusters with a size of 1–2 μm with three different indium compositions. A small fraction (one in 100–1000) of the clusters shows random telegraph noise in luminescence at room temperature. Superlinear dependence of the luminescence switching rate on excitation intensity indicates that the switching is induced by the cooperation of multiple carriers. © 2001 American Institute of Physics. View full abstract»

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  • Stress-stimulated luminescence from ZnAl2O4:Mn

    Page(s): 1068 - 1070
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    We have investigated the stress-stimulated luminescence (SSL) from ZnAl2O4:Mn. Two kinds of ZnAl2O4:Mn samples were synthesized at different reduction conditions to clarify the influence of the structure defects on the SSL property. The SSL intensity was found to be greatly increased by reducing ZnAl2O4:Mn at a high temperature of 1300 °C. The luminescence integrated intensity was about two magnitudes larger than that of conventional ZnAl2O4:Mn. This enhancement is attributed to a large number of trapped carriers in the reduced ZnAl2O4:Mn from the results of thermoluminescence. The SSL spectrum was consistent with the photoluminescence spectrum as well as the afterglow one. It is suggested that the trapped carriers can be excited by stress, and the resultant recombination between excited electrons and holes give rise to an energy which can be transferred to Mn2+ centers to create emission according to the transitions of 4T1 to 6A1. © 2001 American Institute of Physics. View full abstract»

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  • Spike annealing of boron-implanted polycrystalline-silicon on thin SiO2

    Page(s): 1071 - 1073
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    Spike thermal annealing is examined for electrical activation of B implants into 100 nm Si films deposited over 1.5 to 2.4 nm thermally grown SiO2. These structures simulate gate stacks in advanced p-type metal–oxide–Si (PMOS) devices. Spike anneals, at minimized thermal budget, are shown to yield higher carrier concentrations in PMOS polycrystalline-silicon (poly-Si), as compared to conventional rapid thermal annealing. The activation energy for B diffusion through SiO2 is found to be 3.71 to 3.83 eV and near that previously reported for furnace anneals. Boron penetration appears unaffected by photoexcitation from heating lamps. © 2001 American Institute of Physics. View full abstract»

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  • Observation of crossing pores in anodically etched n-GaAs

    Page(s): 1074 - 1076
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    Pores in GaAs in the micrometer range and oriented in 〈111〉 directions have been observed during the anodization of GaAs in aqueous HCl electrolytes. A direct evidence of pores intersection is presented which is a very promising feature for three-dimensional micro- and nanostructuring of III–V compounds for the production of photonic materials. © 2001 American Institute of Physics. View full abstract»

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  • Synthesis of InNxP1-x thin films by N ion implantation

    Page(s): 1077 - 1079
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    Dilute InNxP1-x alloy thin films were synthesized by nitrogen ion implantation into InP using doses corresponding to N mole fraction up to 0.048. In the films with the highest N contents, it was shown using modulated photoreflectance that the fundamental band gap energy was decreased by up to 180 meV. The band gap reduction is similar in magnitude to that observed in epitaxially grown III–NxV1-x alloys. The InNxP1-x layers were thermally stable up to an annealing temperature of 850 °C. Using the recently developed band anticrossing model which relates the band gap reduction to the N content, we estimate that the maximum mole fraction of N achieved in the InNxP1-x alloys is larger than that reported previously for film grown by chemical vapor deposition and exceeds 0.01. © 2001 American Institute of Physics. View full abstract»

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  • Initial stages of molecular-beam epitaxy growth of GaN on 6H-SiC(0001)

    Page(s): 1080 - 1082
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    We studied the atomic H etching of 6H-SiC substrates and the initial stages of GaN/6H-SiC molecular-beam epitaxy growth. Atomic H etched 6H-SiC(0001)Si and (0001¯)C surfaces show a (×)-R30° and a (1×1) reconstruction respectively, with 0.7±0.2 monolayers of remnant O on both surfaces. GaN/6H-SiC(0001)Si growth is initiated by the formation of islands that develop into flat-top terraces through coalescence. Growth steps of one or integer numbers of the GaN atomic bilayer height are observed. GaN grown on 6H-SiC(0001¯)C is rougher with islands of irregular shape. X-ray photoemission spectroscopy studies show that Si 2p and C 1s photoelectron inelastic mean free paths in GaN are 22±1 and 20±1 Å, respectively. © 2001 American Institute of Physics. View full abstract»

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  • Single-electron effects in side-gated point contacts fabricated in low-temperature deposited nanocrystalline silicon films

    Page(s): 1083 - 1085
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    Single-electron effects have been observed up to 60 K in a side-gated point contact device fabricated in nanocrystalline silicon films. The films were phosphorus-doped and deposited at 300 °C by plasma enhanced chemical vapor deposition. Using transmission electron microscopy and Raman spectroscopy, the grain size, crystalline volume fraction, and grain boundary thickness are determined. The single-electron effects are associated with islands formed by crystalline silicon grains ∼4 nm in size, isolated by amorphous silicon regions ∼0.5 nm in thickness. The structural characteristics of the nc-Si film are correlated to the electrical behavior. The electrical transport mechanism at high temperatures is attributed to percolation conduction across a distribution of tunnel barriers with a maximum height of 40 meV. © 2001 American Institute of Physics. View full abstract»

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  • Kelvin probe force microscopy on InAs thin films grown on GaAs giant step structures formed on (110) GaAs vicinal substrates

    Page(s): 1086 - 1088
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    Surface potential measurements on InAs thin films grown on GaAs giant steps were performed by Kelvin probe force microscopy. We found that the removal of the water-related layer from both surfaces on a sample and a tip was very effective to improve the reliability of the surface potential measurements. The measured potential distribution corresponds to the surface corrugation of the InAs thin films. In addition, the InAs layer thickness dependence of the surface InAs Fermi levels is investigated, indicating that the surface Fermi level shifts toward the vacuum level as the increase of the InAs layer thickness. © 2001 American Institute of Physics. View full abstract»

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  • Absorption of nonequilibrium acoustic phonons by low-mobility electrons in GaN

    Page(s): 1089 - 1091
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    We report direct phonon absorption experiments in n-type GaN epitaxial layers grown by molecular beam epitaxy. Nonequilibrium phonons with characteristic energies up to 15 meV (3.5 THz) are injected from a constantan heater. They propagate ballistically through the sapphire substrate, reach the GaN layer, and are absorbed by the degenerate three-dimensional electron gas. The phonon absorption is studied as a function of heater temperature through the effects of phonon induced changes of the device resistivity. The experimental results lead us to the conclusion that in low-mobility GaN, the momentum conservation cutoff for electron-phonon transitions is shifted to higher energy than predicted by standard theory. © 2001 American Institute of Physics. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory