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7 May 2001

Volume 78, Issue 19, pp. 2819-2988

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Transform-limited, narrow-linewidth, terahertz-wave parametric generator

Kodo Kawase, Jun-ichi Shikata, Kazuhiro Imai, and Hiromasa Ito

Appl. Phys. Lett. 78, 2819 (2001); http://dx.doi.org/10.1063/1.1370988 (3 pages) | Cited 49 times

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An injection-seeded nanosecond terahertz (THz) wave parametric generator was demonstrated using nonlinear crystals that were pumped by a single frequency Nd:yttrium–aluminum–garnet laser. Spectrum narrowing to the Fourier transform limit (ν = 1.58 THz, Δν<200 MHz) was achieved by injection seeding the idler wave (near-infrared Stokes). This resulted in a THz-wave output power (900 pJ/pulse, >100 mW peak) approximately 300 times higher than that of a conventional THz-wave parametric generator, which has no injection seeder. This compact system operates at room temperature and promises to be a widely tunable THz-wave source that will compete with free-electron lasers and p-Ge lasers. © 2001 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
42.30.Kq Fourier optics

Divergence behavior due to surface channeling in capillary optics

G. Cappuccio, S. B. Dabagov, C. Gramaccioni, and A. Pifferi

Appl. Phys. Lett. 78, 2822 (2001); http://dx.doi.org/10.1063/1.1370117 (3 pages) | Cited 10 times

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Recent studies on the transmitting and focusing properties of capillary optical systems have shown that several unexpected effects take place during the experiments. One such effect is a decrease in the beam divergence behind the capillary structures. In this letter, we present results on x-ray scattering at grazing angles inside capillaries. During x-ray propagation in capillary channels, there is a strong angular redistribution of the beam, which has been explained in the framework of the wave scattering theory. © 2001 American Institute of Physics.
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41.50.+h X-ray beams and x-ray optics

Passive mode-locking in 1.3 μm two-section InAs quantum dot lasers

Xiaodong Huang, A. Stintz, Hua Li, L. F. Lester, Julian Cheng, and K. J. Malloy

Appl. Phys. Lett. 78, 2825 (2001); http://dx.doi.org/10.1063/1.1371244 (3 pages) | Cited 58 times

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Passive mode locking was achieved at 1.3 μm in oxide-confined, two-section, bistable quantum dot (QD) lasers with an integrated intracavity QD saturable absorber. Fully mode-locked pulses at a repetition rate of 7.4 GHz with a duration of 17 ps were observed under appropriate bias conditions. No self-pulsation accompanied the mode locking. These results suggest that a carefully designed QD laser is a candidate for ultrashort pulse generation. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Time-resolved probing of the Purcell effect for InAs quantum boxes in GaAs microdisks

B. Gayral, J.-M. Gérard, B. Sermage, A. Lemaître, and C. Dupuis

Appl. Phys. Lett. 78, 2828 (2001); http://dx.doi.org/10.1063/1.1370123 (3 pages) | Cited 25 times

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We studied, by time-resolved microphotoluminescence (PL), the spontaneous emission dynamics of InAs/GaAs quantum boxes coupled to high Purcell factor (up to 155) whispering gallery modes of microdisks under nonresonant excitation. A global shortening of the PL decay by a factor of up to 12 was observed for the collection of quantum boxes on resonance with the modes. This behavior is well understood when the random distribution of the quantum boxes and the finite relaxation rate of the carriers are taken into account. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.Hc Quantum dots
81.05.Ea III-V semiconductors
73.21.La Quantum dots
81.07.Ta Quantum dots
78.47.-p Spectroscopy of solid state dynamics

One-dimensional cuprate as a nonlinear optical material for ultrafast all-optical switching

M. Ashida, T. Ogasawara, Y. Tokura, S. Uchida, S. Mazumdar, and M. Kuwata-Gonokami

Appl. Phys. Lett. 78, 2831 (2001); http://dx.doi.org/10.1063/1.1370546 (3 pages) | Cited 22 times

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We examine the feasibility of ultrafast all-optical switching utilizing a one-dimensional cuprate Sr2CuO3 operable within the optical fiber communication window at room temperature by using the pump-probe spectroscopy and Z-scan measurements. The strength of the interband two-photon absorption in Sr2CuO3 is much larger than that of conventional semiconductors, and is comparable to the largest reported values in π-conjugated polymers. The intensity-dependent refractive index, however, is considerably larger than that of polymeric materials. We further show that the recovery of optical transparency after the photoinjection of carriers lies within picosecond time scale. Large nonlinearity, ultrafast response, and high damage threshold make the one-dimensional cuprate a potential material for multiterabits/second rate all-optical switch. © 2001 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Grating-tuned external-cavity quantum-cascade semiconductor lasers

G. P. Luo, C. Peng, H. Q. Le, S. S. Pei, W.-Y. Hwang, B. Ishaug, J. Um, James N. Baillargeon, and C.-H. Lin

Appl. Phys. Lett. 78, 2834 (2001); http://dx.doi.org/10.1063/1.1371524 (3 pages) | Cited 38 times

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Grating-coupled external-cavity quantum-cascade lasers were studied for temperatures from 80 to 230 K. At 80 K, a tuning range of ∼65–88 nm are obtained for 4.5 and 5.1 μm laser amplifiers, respectively. The tuning ranges for both narrowed substantially with increasing temperature, to ∼23 nm at 203 K. The threshold varied slowly versus wavelength, while the efficiency appeared to be close to optimum toward wavelengths shorter than the free running wavelength. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
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Energetics of vacuum arc cathode spots

André Anders

Appl. Phys. Lett. 78, 2837 (2001); http://dx.doi.org/10.1063/1.1370541 (3 pages) | Cited 6 times

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Vacuum arcs need to generate the current-carrying plasma at cathode spots. The cohesive energy of the cathode material determines the energy the arc needs to provide for the phase transitions of the cathode material. As recent experiments confirm, the greater the cohesive energy the higher the burning voltage (“cohesive energy rule”). This relation is founded in the energy balance of cathode spot operation, regardless of the specific cathode mechanisms involved. A greater power input, as determined by the cohesive energy via the cohesive energy rule, leads to enhanced power output in various forms such as enhanced electron temperature, ion charge states, and ion velocity. Using the Cohesive Energy Rule, secondary relations such as the well known relation between boiling point of the cathode and average ion charge state can be explained. © 2001 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs

Energy deposition at front and rear surfaces during picosecond laser interaction with fused silica

A. Salleo, F. Y. Génin, M. D. Feit, A. M. Rubenchik, T. Sands, S. S. Mao, and R. E. Russo

Appl. Phys. Lett. 78, 2840 (2001); http://dx.doi.org/10.1063/1.1362332 (3 pages) | Cited 13 times

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The difference between front-surface and rear-surface energy deposition of a 35 ps laser pulse (λ=1064 nm) in fused silica was investigated using shadowgraphic and laser-deflection techniques. Shock waves were observed in the glass and in air. Shock waves generated in air at the front surface are stronger than at the rear surface. Less than 35% of the energy incident on the surface drives the air shock waves at the rear surface. Up to 90% of the incident energy drives the air shock waves at the front surface. Laser-plasma interaction is responsible for this difference and for limiting the amount of energy deposited inside the sample during front-surface ablation. Energy deposition at the rear surface is mostly limited by self-focusing inside the material. © 2001 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
62.50.-p High-pressure effects in solids and liquids
52.38.Mf Laser ablation
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Spins and microstructure of hydrogenated amorphous carbon: A multiple frequency electron paramagnetic resonance study

H. J. von Bardeleben, J. L. Cantin, A. Zeinert, B. Racine, K. Zellama, and P. N. Hai

Appl. Phys. Lett. 78, 2843 (2001); http://dx.doi.org/10.1063/1.1370980 (3 pages) | Cited 17 times

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Polymer-like and diamond-like hydrogenated amorphous carbon films, characterized by high spin concentrations of 1020 cm−3, have been studied by multiple frequency electron paramagnetic resonance (EPR) spectroscopy at 9, 35, and 94 GHz. Whereas the low-frequency measurements show only one single symmetric EPR line, the high-frequency measurements reveal the anisotropic nature of the g tensor. They show the presence of two different paramagnetic centers with anisotropic g tensors of g∥(1) = 2.005, g⊥(1) ≈ 2.003, and g∥(2) = 2.010, g⊥(2) ≈ 2.003. We attribute both to localized π states on nanosized sp2 graphitic clusters. The g∥ values of the g tensors, which are correlated to the size of the graphite like carbon clusters, indicate two different cluster sizes with values below 50 Å. © 2001 American Institute of Physics.
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61.43.Er Other amorphous solids
76.30.-v Electron paramagnetic resonance and relaxation
81.05.U- Carbon/carbon-based materials
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
68.55.-a Thin film structure and morphology

Coherent measurement of the dispersive curves of an elastic waveguide

Hailan Zhang, Shuwu Dai, and Chengyu Zhang

Appl. Phys. Lett. 78, 2846 (2001); http://dx.doi.org/10.1063/1.1370542 (3 pages) | Cited 2 times

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A coherent method is proposed to measure the dispersive curves of elastic waveguides. The use of the phase information makes the measurement more precise and stable than traditional noncoherent methods. The principle of the method should work well for other kinds of waveguides. © 2001 American Institute of Physics.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
68.35.Iv Acoustical properties
43.58.Dj Sound velocity

Strong photoluminescence emission from polycrystalline GaN layers grown on W, Mo, Ta, and Nb metal substrates

K. Yamada, H. Asahi, H. Tampo, Y. Imanishi, K. Ohnishi, and K. Asami

Appl. Phys. Lett. 78, 2849 (2001); http://dx.doi.org/10.1063/1.1371528 (3 pages) | Cited 21 times

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Polycrystalline GaN layers were grown on W, Mo, Ta, and Nb metal substrates by gas-source molecular-beam epitaxy using an ion-removal, electron-cyclotron-resonance radical cell. X-ray diffraction rocking curves showed preferential GaN(0002) or GaN(10–11) orientations. The grain sizes ranged from 100 to 800 nm. Strong photoluminescence (PL) emission without yellow luminescence was observed from these polycrystalline GaN layers. At 77 K, PL peaks at 3.46 and 3.26 eV were observed, and their temperature dependence fit a simple relation based on the number of phonons. The higher-energy peak probably was due to the free excitonic transition in hexagonal GaN. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.35.-y Excitons and related phenomena

Strain-driven self-positioning of micromachined structures

Pablo O. Vaccaro, Kazuyoshi Kubota, and Tahito Aida

Appl. Phys. Lett. 78, 2852 (2001); http://dx.doi.org/10.1063/1.1371525 (3 pages) | Cited 58 times

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We introduce a method to make self-positioned micromachined structures by using the strain in a pair of lattice-mismatched epitaxial layers. This method allows the fabrication of simple and robust hinges for movable parts, and it can be applied to any pair of lattice-mismatched epitaxial layers, in semiconductors or metals. As an application example, a standing mirror was fabricated. A multilayer structure including an AlGaAs/GaAs dielectric mirror and an InGaAs strained layer was grown by molecular-beam epitaxy on a GaAs substrate. After releasing the multilayer structure from the substrate by selective etching, it moved to its final position powered by the strain release in the InGaAs layer. © 2001 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling
06.60.Sx Positioning and alignment; manipulating, remote handling
42.79.Bh Lenses, prisms and mirrors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.86.+b Optical workshop techniques

Incorporation of beryllium on the clean and indium-terminated GaN(0001) surface

John E. Northrup

Appl. Phys. Lett. 78, 2855 (2001); http://dx.doi.org/10.1063/1.1368369 (3 pages) | Cited 4 times

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First-principles calculations of the energetics of Be incorporation in various sites on clean and indium-terminated GaN(0001) are presented. On the clean Ga-rich surface the Be atom prefers a surface substitutional Ga site over a near-surface interstitial site by about 1.0 eV, thus suggesting that interstitial concentrations could be suppressed near the surface during growth. Calculations for In-terminated surfaces suggest that it is possible to enhance incorporation of Be on the Ga site by performing the growth under conditions in which Be compensates compressive stress resulting from In incorporation. © 2001 American Institute of Physics.
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81.65.Ps Polishing, grinding, surface finishing
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters

Growth of high-quality GaN on Si(111) substrate by ultrahigh vacuum chemical vapor deposition

Min-Ho Kim, Young-Churl Bang, Nae-Man Park, Chel-Jong Choi, Tae-Yeon Seong, and Seong-Ju Park

Appl. Phys. Lett. 78, 2858 (2001); http://dx.doi.org/10.1063/1.1371539 (3 pages) | Cited 24 times

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An ultrahigh vacuum chemical vapor deposition (UHVCVD) system was employed to grow high-quality GaN on a Si (111) substrate using a thin AlN buffer layer. X-ray diffraction, high-resolution electron microscopy (HREM), and photoluminescence (PL) data indicate that a single crystalline GaN layer with a wurtzite structure was epitaxially grown on a silicon substrate. The full width at half maximum (FWHM) of the x-ray rocking curve for the GaN (0002) diffraction was 16.7 arc min. A cross-sectional HREM image showed an amorphous SiNx layer at the Si/AlN interface, as well as stacking faults and inversion domain boundaries in the GaN epilayer. An intense PL emission line, which is associated with the recombination of the donor bound exciton, was observed at 10 K PL spectra (FWHM=6.8 meV) and a strong band edge emission was obtained (FWHM=33 meV) as well, even at room temperature. These results indicate that high-quality GaN can be grown on Si (111) substrates using a UHVCVD growth method. © 2001 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Excitonic transitions in ZnO/MgZnO quantum well heterostructures

Giuliano Coli and K. K. Bajaj

Appl. Phys. Lett. 78, 2861 (2001); http://dx.doi.org/10.1063/1.1370116 (3 pages) | Cited 89 times

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In this work we present the calculation of the excitonic transition energies in ZnO/MgZnO quantum well heterostructures, accounting for the effects of the exciton–phonon interaction. The results of our calculations clearly show that the description of the electron–hole interaction by means of the static screened Coulomb potential and the use of the polaron masses for the electron and the hole leads to a poor agreement with available experimental data. On the other hand, including the exciton–phonon interaction in the calculation of the exciton binding energies, leads to the values of the excitonic transitions which agree very well with the recently published experimental data. A critical discussion of the choice of the physical parameters used in ZnO is also presented, which leads us to suggest a value for the heavy-hole band mass of 0.78m0 and a conduction-valence band ratio in the range 60/40–70/30. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.kk Phonon interactions with other quasiparticles
71.38.-k Polarons and electron-phonon interactions

Lattice parameter in GaNAs epilayers on GaAs: Deviation from Vegard’s law

Wei Li, Markus Pessa, and Jari Likonen

Appl. Phys. Lett. 78, 2864 (2001); http://dx.doi.org/10.1063/1.1370549 (3 pages) | Cited 56 times

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The N content and lattice parameter of GaNxAs1−xepilayers on GaAs (0<x<0.03) were determined by secondary ion mass spectroscopy and x-ray diffraction measurements, respectively. A significant deviation of the lattice parameter variation in GaNxAs1−x from Vegard’s law between GaAs and cubic GaN was observed, which leads to overestimation of the nitrogen content by up to 30% for x ⩽ 2.5%. The physical origin of this negative deviation is discussed. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
81.05.Ea III-V semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Direct observation of voids in the vacancy excess region of ion bombarded silicon

J. S. Williams, M. J. Conway, B. C. Williams, and J. Wong-Leung

Appl. Phys. Lett. 78, 2867 (2001); http://dx.doi.org/10.1063/1.1352662 (3 pages) | Cited 15 times

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The results reported in this letter indicate that the spatial separation of the vacancy and interstitial excesses which result from ion bombardment gives rise to stable voids upon annealing at 850 °C even for implants where the projected ion range is only of the order of a few thousand Ångstrom. Such voids have been observed directly by transmission electron microscopy. Furthermore, in cases where both voids and interstitial-based defects are present at different depths, it is found that Au has a strong preference for decorating void surfaces and hence Au can, indeed, be used as a selective detector of open volume defects in Si. © 2001 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing

Helium/deuterium coimplanted silicon: A thermal desorption spectrometry investigation

F. Corni, C. Nobili, R. Tonini, G. Ottaviani, and M. Tonelli

Appl. Phys. Lett. 78, 2870 (2001); http://dx.doi.org/10.1063/1.1344568 (3 pages) | Cited 9 times

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Thermal desorption spectrometry has been applied to investigate the blistering and exfoliation phenomena which occur at the surface of a p-type (100) silicon wafer coimplanted with helium and deuterium. During the heat treatments in linear temperature ramp, an explosive emission of both gases occurs. The phenomenon is kinetically controlled with an effective activation energy of 1.3±0.2 eV. In addition, the desorption spectra present a second contribution, attributed to deuterium emission from buried cavities. Also in this case, the process is kinetically controlled with an effective activation energy of 1.9±0.3 eV. Thermal desorption spectrometry is a suitable technique to have information about various phenomena which occur during blistering and exfoliation. © 2001 American Institute of Physics.
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68.43.Vx Thermal desorption
81.40.Gh Other heat and thermomechanical treatments
81.05.Cy Elemental semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
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Scanning Kelvin probe microscopy characterization of dislocations in III-nitrides grown by metalorganic chemical vapor deposition

G. Koley and M. G. Spencer

Appl. Phys. Lett. 78, 2873 (2001); http://dx.doi.org/10.1063/1.1369390 (3 pages) | Cited 35 times

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Scanning Kelvin probe microscopy has been used in conjunction with noncontact atomic force microscopy for characterizing dislocations in n-GaN and Al0.35Ga0.65N/GaN heterostructures. The surface potential variations around the dislocations present in the Al0.35Ga0.65N/GaN heterostructure have been observed to be 0.1–0.2 V with full width at half maximums (FWHMs) of 100–200 nm. On the other hand, n-GaN shows potential variations of 0.3–0.5 V having FWHMs of 20–50 nm. The dislocations (present in densities of ∼ 109 cm−2) have been found to be negatively charged for both n-GaN and Al0.35Ga0.65N/GaN heterostructure samples. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Mass transport regrowth of GaN for ohmic contacts to AlGaN/GaN

Sten Heikman, Stacia Keller, Steven P. DenBaars, and Umesh K. Mishra

Appl. Phys. Lett. 78, 2876 (2001); http://dx.doi.org/10.1063/1.1369609 (3 pages) | Cited 22 times

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Ohmic contacts were fabricated for AlGaN/GaN high-electron-mobility transistors by selective-area mass transport regrowth of GaN. The contact resistance ranged from 0.23 to 1.26 Ω mm for different contact areas and geometries. The average resistivity of the autodoped regrown GaN was measured to 4×10−3 Ω cm. Devices with regrown contacts were fabricated, achieving a transconductance of 210 mS/mm. The technique provides a low-cost regrowth process, with applications in particular for high Al-composition AlGaN/GaN devices. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Charge transfer of carriers by interband photoexcitation in asymmetric GaAs/AlGaAs coupled quantum wells

M. Levy, Yu. L. Khait, R. Beserman, A. Sa’ar, V. Thierry-Mieg, and R. Planel

Appl. Phys. Lett. 78, 2879 (2001); http://dx.doi.org/10.1063/1.1369413 (3 pages) | Cited 1 time

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The influence of interband photoexcitation intensity on the photoluminescence line shape was investigated in GaAs/AlGaAs modulation-doped asymmetric structure composed of a wide quantum well weakly coupled to a narrow quantum well. The emission spectra show a broadening and a narrowing of the linewidths from the wide quantum well and from the narrow quantum well, respectively, with increasing laser power. In addition, we observe a fast increase of the emission intensity from the narrow quantum well with respect to that from the wide quantum well. These processes are shown to be the result of carrier transfer into the narrow quantum well. We propose a charge transfer model to explain semiquantitatively our results. © 2001 American Institute of Physics.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Transient photoluminescence of defect transitions in freestanding GaN

M. A. Reshchikov, H. Morkoç, S. S. Park, and K. Y. Lee

Appl. Phys. Lett. 78, 2882 (2001); http://dx.doi.org/10.1063/1.1370119 (3 pages) | Cited 14 times

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Deep level defects responsible for the 2.4 eV photoluminescence (PL) band in a freestanding GaN template were studied by transient photoluminescence. A nonexponential decay of PL intensity observed at low temperature is attributed to a donor–acceptor pair recombination involving a shallow donor and a deep acceptor. At room temperature, a single-exponential PL decay with a lifetime of 30 μs was observed at the high-energy side of the band, whereas the second component with a lifetime of about 750 μs was detected at the low-energy side of the band. The PL decay and transformation of the PL spectrum at room temperature can be explained by transitions from the conduction band to two deep acceptors. Electron-capture cross section has been estimated as 4×10−21 and 10−19 cm2 for the yellow and green bands, respectively, contributing to the broad 2.4 eV band. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Thickness effects on imprint in chemical-solution-derived (Pb, La)(Zr, Ti)O3 thin films

Seung-Hyun Kim, Hyun-Jung Woo, Jowoong Ha, Cheol Seong Hwang, Hae Ryoung Kim, and Angus I. Kingon

Appl. Phys. Lett. 78, 2885 (2001); http://dx.doi.org/10.1063/1.1370989 (3 pages) | Cited 14 times

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The film thickness-dependent imprinting behavior (voltage shift) of (Pb, La)(Zr, Ti)O3 capacitors was evaluated by a thermal stress process under a remanence bias. The remanent polarization (Pr) was found to be almost independent of the film thickness whereas in the 50–300 nm range the relative dielectric constant (εr) increased linearly with the square root of the film thickness. It was found that the voltage shift, which was attributed to the accumulation of charged defects near the electrode interface, also increased linearly with increasing film thickness. In addition, the charge accumulated thickness varied with the square root of the film thickness. This was established from a simple assumption that the level of charge accumulation is determined by the product of the total amount of charged defects (total film thickness×charged defect density) and the internal field that is generated by the Pr. Therefore, the imprint is much more a bulk-related degradation phenomenon compared to the fatigue. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.-e Ferroelectricity and antiferroelectricity
84.32.Tt Capacitors
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)
68.55.-a Thin film structure and morphology

Wide bandwidth millimeter wave mixer using a diffusion cooled two-dimensional electron gas

Mark Lee, L. N. Pfeiffer, K. W. West, and K. W. Baldwin

Appl. Phys. Lett. 78, 2888 (2001); http://dx.doi.org/10.1063/1.1370982 (3 pages) | Cited 7 times

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Very fast millimeter wave mixers have been fabricated from a high mobility two-dimensional electron gas (2DEG) in a GaAs–AlGaAs heterostructure. Using a 115 GHz local oscillator, intermediate frequency (IF) bandwidths exceeding 20 GHz have been obtained for channel lengths L of a few microns. Operating at 77 K, the IF bandwidth scales as L−2, indicating that the response speed is determined by the diffusion transit time of hot electrons to the leads. © 2001 American Institute of Physics.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.30.-z Semiconductor devices
72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Band-gap engineering in sputter-deposited ScxGa1−xN

M. E. Little and M. E. Kordesch

Appl. Phys. Lett. 78, 2891 (2001); http://dx.doi.org/10.1063/1.1370548 (2 pages) | Cited 33 times

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Reactive sputtering was used to grow thin films of ScxGa1−xN with scandium concentration of 20%–70% on quartz substrates at temperatures of 300–675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with composition between 2.0 and 3.5 eV. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys not heterogeneous mixtures. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
71.20.Nr Semiconductor compounds
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
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