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16 Aug 1999

Volume 75, Issue 7, pp. 885-1026

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Single-mode, single-lobe operation of surface-emitting, second-order distributed feedback lasers

J. Lopez, G. Witjaksono, and D. Botez

Appl. Phys. Lett. 75, 885 (1999); http://dx.doi.org/10.1063/1.124544 (3 pages) | Cited 3 times

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A thin p-cladding InGaAs/InGaP/GaAs laser structure (λ = 0.977 μm) with a second-order Au/air grating (70% duty cycle) and asymmetrically coated (30%, 5% reflectivity) cleaved facets emits in a diffraction-limited (0.11°) single lobe in a direction virtually normal to the chip surface. The near-field pattern corresponds to (grating) phase shifts of 10° and 40° at the low- and high-reflectivity cleaved-mirror facets. An analysis of 30%/0% coated, 500-μm-long devices shows that single-lobe surface emission occurs for a wide variation in grating phase with respect to the high reflectivity mirror, ΔϕHR: 10°–80°. For 99%/0% coated devices, single-lobe emission occurs with relatively uniform near-field intensity profile and external differential quantum efficiency ηd around 20% for ΔϕHR values close to π/4 (i.e., in the 45°–65° range). Single-lobe emission normal to the chip surface (i.e., symmetric-mode lasing) can then be obtained from devices without cleaved mirrors by introducing a phase shift close to π/2 in the center of the second-order grating. For the structure used, a phase shift of 90°–130° in the center of 1-mm-long gratings is found to provide single-lobe surface emission with substantially uniform near-field profile, and ηd values as high as 22%. Increasing the grating-section length increases ηd (e.g., 35% for 1.5-mm-long gratings) at some price in near-field uniformity. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings
42.79.Bh Lenses, prisms and mirrors

White-light-emitting organic electroluminescent devices based on interlayer sequential energy transfer

R. S. Deshpande, V. Bulović, and S. R. Forrest

Appl. Phys. Lett. 75, 888 (1999); http://dx.doi.org/10.1063/1.124250 (3 pages) | Cited 184 times

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We demonstrate efficient, molecular organic white-light-emitting devices using vacuum-deposited thin films of red luminescent [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H, 5H-benzo [ij] quinolizin-9-yl) ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2), doped into blue-emitting 4, 4′ bis [N-1-napthyl-N-phenyl-amino]biphenyl (α-NPD), and green-emitting tris-(8-hydroxyquinolinato) aluminum(III) (AlQ3). The luminescent layers are separated by a hole-blocking layer of 2,9-dimethyl, 4,7-diphenyl, 1,10-phenanthroline (BCP), whose thickness is on the order of a typical Förster transfer radius of 30–40 Å. Excitons formed on α-NPD sequentially transfer their energy via a Förster mechanism to AlQ3 across the BCP layer, and from AlQ3 to DCM2. This interlayer sequential energy transfer results in partial excitation of all three molecular species, thereby producing white light emission. The thickness of the blocking layer and the concentration of DCM2 in α-NPD permit the tuning of the device spectrum to achieve a balanced white emission with Commission Internationale d’Eclairage chromaticity coordinates of (0.33, 0.33). The spectrum is largely insensitive to the drive current, and the devices have a maximum luminance of 13 500 cd/m2. At a luminance of 100 cd/m2, the quantum and power efficiencies are 0.5% and 0.35 lm/W, respectively. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
71.35.-y Excitons and related phenomena

Compensated dispersion tuning in harmonically mode-locked fiber laser

K. Chan and C. Shu

Appl. Phys. Lett. 75, 891 (1999); http://dx.doi.org/10.1063/1.124545 (3 pages) | Cited 6 times

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Electrical tuning of wavelength has been demonstrated in a harmonically mode-locked fiber laser using a compensated dispersion-tuning approach. The cavity consists of a standard single-mode fiber (SMF) and a dispersion-compensated fiber (DCF), providing equal and opposite group velocity dispersion to wavelength components around 1.55 μm. Tuning is achieved by controlling the delay time between electrical pulse signals applied to two modulators connecting the SMF and the DCF. The tuning relation exhibits a linear characteristic and matches with the calculated result. A 21.5 nm tuning range is obtained with an extinction ratio as high as 47 dB at a constant operating frequency of 1 GHz. © 1999 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Low-threshold optically pumped lasing at 444 nm at room temperature with high characteristic temperature from Be-chalcogenide-based single-quantum-well laser structures

J. H. Chang, M. W. Cho, K. Godo, H. Makino, T. Yao, M. Y. Shen, and T. Goto

Appl. Phys. Lett. 75, 894 (1999); http://dx.doi.org/10.1063/1.124546 (3 pages) | Cited 8 times

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We have achieved low-threshold optically pumped lasing at 444 nm at room temperature with high characteristic temperature (T0) from ZnSe/ZnMgBeSe single-quantum-well structures. The threshold intensity is as low as 15 kW cm−2, while T0 value is as high as 166 K. Lasing is observed up to 473 K. Lasing wavelength of 444 nm at room temperature is the shortest wavelength ever achieved in ZnSe-based laser diode structures. The laser structure includes a single ZnMgBeSe/ZnSe/ZnMgBeSe quantum well with a ZnSe well thickness of 4 nm. The (004) x-ray diffraction rocking curve of the ZnMgBeSe quaternary cladding layers shows a sharp diffraction peak with a full width at half maximum of 21 arcsec which is in contrast to that from a ZnMgSSe cladding layer showing much broader multiple peaks. The observed lasing features are partly ascribed to high crystal quality of the ZnMgBeSe layers and type-I band alignment, as has been supported by photoluminescence in addition to x-ray diffraction measurements. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Half-symmetric cavity microelectromechanically tunable vertical cavity surface emitting lasers with single spatial mode operating near 950 nm

Peidong Wang, Parviz Tayebati, Daryoosh Vakhshoori, Chih-Cheng Lu, Masud Azimi, and Robert N. Sacks

Appl. Phys. Lett. 75, 897 (1999); http://dx.doi.org/10.1063/1.124251 (2 pages) | Cited 4 times

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We describe tunable vertical cavity surface emitting lasers with a half-symmetric cavity structure. The cavity is realized by inducing a curvature (R ∼ 300 μm) in the top movable dielectric mirror. This half-symmetric microcavity forces lasing oscillations in a single fundamental spatial mode with a side-mode suppression ratio of >25 dB. Continuous wavelength tuning of 44 nm was achieved microelectromechanically with a tuning voltage of 14 V. The device operates near 950 nm with maximum power output of ∼0.9 mW. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Optically pumped type-II interband terahertz lasers

I. Vurgaftman and J. R. Meyer

Appl. Phys. Lett. 75, 899 (1999); http://dx.doi.org/10.1063/1.124547 (3 pages) | Cited 10 times

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Optically pumped terahertz lasers based on interband transitions in type-II antimonide heterostructures are proposed and modeled in detail. At cryogenic temperatures, the activated nature of the Auger and phonon-assisted mechanisms should provide substantially longer nonradiative lifetimes and higher gains than are attainable with intersubband devices. For emission at λ = 27 μm, pulsed operation is projected up to 60 K, and >25 mW of cw output power is calculated for T = 30 K. At T = 4 K, lasing is expected out to wavelengths as long as 100 μm. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Large third-order optical nonlinearity in SrBi2Ta2O9 thin films by pulsed laser deposition

W. F. Zhang, M. S. Zhang, Z. Yin, Y. Z. Gu, Z. L. Du, and B. L. Yu

Appl. Phys. Lett. 75, 902 (1999); http://dx.doi.org/10.1063/1.124548 (3 pages) | Cited 23 times

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Well-crystallized SrBi2Ta2O9 (SBT) thin films with good surface morphology were prepared on quartz substrates by the pulsed laser deposition technique at a deposition temperature of 750 °C. The third-order nonlinear optical properties of the films were measured by the Z-scan technique. The magnitude and sign of the nonlinear refractive index n2 were determined, as was the negative sign, which indicated a self-defocusing optical nonlinearity. A nonlinear refractive index as high as 1.9×10−6 esu was displayed in the SBT thin film. These results show that SBT ferroelectric thin films have potential applications in nonlinear optics. © 1999 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Optical properties of three-dimensional photonic crystals based on III–V semiconductors at infrared to near-infrared wavelengths

Susumu Noda, Noritsugu Yamamoto, Hideaki Kobayashi, Makoto Okano, and Katsuhiro Tomoda

Appl. Phys. Lett. 75, 905 (1999); http://dx.doi.org/10.1063/1.124549 (3 pages) | Cited 58 times

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The optical properties of three-dimensional photonic crystals based on III–V semiconductors are investigated. The crystals are constructed by stacking GaAs (or InP) stripes with a wafer-fusion technique to form an asymmetric face-centered-cubic structure. It is shown that a crystal with eight-stacked layers (two units), whose period is 4 μm, has a considerable band-gap effect (∼30 dB attenuation) in the transmission spectrum at infrared wavelengths (5–10 μm), and the band gap is observed independently of the incident angles. Then, a crystal with four-stacked layers with a submicron period is constructed, and a clear band gap (attenuation up to 10 dB) is successfully observed at near-infrared wavelengths (1–1.5 μm). © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials

The dual wavelength Bi-vertical cavity surface-emitting laser

J. F. Carlin, R. P. Stanley, P. Pellandini, U. Oesterle, and M. Ilegems

Appl. Phys. Lett. 75, 908 (1999); http://dx.doi.org/10.1063/1.124550 (3 pages) | Cited 18 times

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We present a monolithically integrated vertical coupled cavity surface-emitting laser diode which exhibits stable laser emission at two design wavelengths simultaneously. The device consists of two slightly asymmetric coupled vertical cavities containing strained InGaAs quantum wells as the gain media. The shorter cavity is pumped electrically. Lasing starts on the short wavelength mode at 927 nm. The laser emission then acts as an optical pump for the quantum wells in the longer cavity and provides additional gain for the long wavelength mode, resulting in a subsequent laser emission at 955 nm. With increasing injection current, the device maintains stable emission at the two wavelengths. The threshold for dual lasing is 4 kA/cm2 and dual lasing is stable over six times the threshold. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.82.Cr Fabrication techniques; lithography, pattern transfer
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Focusing of high-current, large-area, heavy-ion beams with an electrostatic plasma lens

A. A. Goncharov, I. M. Protsenko, G. Yu. Yushkov, and I. G. Brown

Appl. Phys. Lett. 75, 911 (1999); http://dx.doi.org/10.1063/1.124551 (3 pages) | Cited 17 times

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We report on measurements of the focusing of high-current, large-area beams of heavy metal ions using an electrostatic plasma lens. Tantalum ion beams were formed by a repetitively pulsed vacuum arc ion source, with energy in the 100 keV range, current up to 0.5 A, initial beam diameter 10 cm, and pulse length 250 μs. The plasma lens was of internal diameter 10 cm and length 20 cm, and had nine electrostatic ring electrodes with potential applied to the central electrode of up to 7 kV, in the presence of a pulsed magnetic field of up to 800 G. The current-density profile of the downstream, focused, ion beam was measured with a radially moveable, magnetically suppressed, Faraday cup. The tantalum ion-beam current density at the focus was compressed by a factor of up to 30. The results are important in that they provide a demonstration of a means of manipulating high-current ion beams without associated space-charge blowup. © 1999 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
52.75.-d Plasma devices
41.85.Ne Electrostatic lenses, septa
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Segregation and strain relaxation in Au/Ni multilayers: An in situ experiment

S. Labat, P. Gergaud, O. Thomas, B. Gilles, and A. Marty

Appl. Phys. Lett. 75, 914 (1999); http://dx.doi.org/10.1063/1.124552 (3 pages) | Cited 18 times

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We report on in situ real-time measurements of both stress and strain during growth of ultrathin layers, with submonolayer sensitivity. The in-plane lattice parameter is measured by reflection high energy electron diffraction and the stress is determined via the curvature measurements. The system studied is Au/Ni (i.e., Au on Ni and Ni on Au). We have evidenced a large asymmetry in the two different growths: Au (on Ni) shows a progressive elastic strain relaxation, whereas Ni (on Au) exhibits a strong interplay between the stress and the interfacial mixing. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.35.Gy Mechanical properties; surface strains

Size stabilization of arsenic precipitates in nonstoichiometric GaAs-based compounds

C.-Y. Hung, J. S. Harris, A. F. Marshall, and R. A. Kiehl

Appl. Phys. Lett. 75, 917 (1999); http://dx.doi.org/10.1063/1.124553 (3 pages) | Cited 2 times

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A narrowing of the size distribution of arsenic precipitates in nonstoichiometric GaAs-based compounds is observed during annealing for precipitates in the small size regime of a few nanometers. This improvement in size uniformity is in marked contrast to what is observed for larger precipitates, which coarsen with a widening distribution similar to that of classical Ostwald ripening. Inverse coarsening caused by an elastic interaction between small precipitates due to coherency strain is a possible mechanism for this interesting and potentially useful behavior. © 1999 American Institute of Physics.
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81.30.Mh Solid-phase precipitation
81.05.Ea III-V semiconductors
64.75.-g Phase equilibria
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.40.Gh Other heat and thermomechanical treatments

Measurement of mechanical resonance and losses in nanometer scale silicon wires

Dustin W. Carr, S. Evoy, L. Sekaric, H. G. Craighead, and J. M. Parpia

Appl. Phys. Lett. 75, 920 (1999); http://dx.doi.org/10.1063/1.124554 (3 pages) | Cited 152 times

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We present data on nanofabricated suspended silicon wires driven at resonance. The wires are electrostatically driven and detected optically. We have observed wires with widths as small as 45 nm and resonant frequencies as high as 380 MHz. We see a strong dependence of the resonant quality factor on the surface to volume ratio. © 1999 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Interdiffused quantum-well infrared photodetectors for color sensitive arrays

M. B. Johnston, M. Gal, Na Li, Zhanghai Chen, Xingquan Liu, Ning Li, Wei Lu, S. C. Shen, L. Fu, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 75, 923 (1999); http://dx.doi.org/10.1063/1.124555 (3 pages) | Cited 9 times

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Proton implantation and rapid thermal annealing were used to tune the infrared spectral response of quantum-well infrared photodetectors (QWIP) by up to 1.4 μm. Multiple proton implants at energies between 200 and 420 keV were used to create homogeneous quantum-well intermixing throughout the device’s multiple-quantum-well structure. Photoluminescence and spectral response measurements were used to study the effect of proton implantation on QWIPs for a series of doses up to 3.5×1015 protons cm−2. By using a mask during implantation, a method of constructing a color sensitive array is proposed. © 1999 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.uj III-V and II-VI semiconductors
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Kinetic Monte Carlo simulations of nucleation on a surface with periodic strain: Spatial ordering and island-size distribution

Thomas R. Mattsson and Horia Metiu

Appl. Phys. Lett. 75, 926 (1999); http://dx.doi.org/10.1063/1.124556 (3 pages) | Cited 22 times

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We use kinetic Monte Carlo simulations to study nucleation of adsorbate islands on a solid surface on which a periodic strain field has been imposed. We show that, in spite of its very small effect on the diffusion constant of the atoms, the field orders the ensemble of islands. Better ordering and a narrower size distribution are obtained when the ensemble of islands produced by nucleation is coarsened. © 1999 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
64.60.Q- Nucleation
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Rr General statistical methods
68.35.Fx Diffusion; interface formation

Boron nitride nanotubes, webs, and coexisting amorphous phase formed by the plasma jet method

Yoshiki Shimizu, Yusuke Moriyoshi, Hideki Tanaka, and Shojiro Komatsu

Appl. Phys. Lett. 75, 929 (1999); http://dx.doi.org/10.1063/1.124557 (3 pages) | Cited 20 times

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Boron nitride (BN) nanotubes were prepared by a high-temperature plasma jet method. While the BN nanotubes were found in quantity on the surface of a BN sintered disk, amorphous BN webs were found dominant in the water-cooled collector. These structures were studied on the basis of transmission electron microscopy observations. One of them was composed of 21 layers grown coaxially with a regular spacing of 0.34 nm and their tip ends were terminated with parallel bases of the coaxial cylindrical shapes. The diameter of the innermost tube was 0.6 nm and this dimension is in fairly good agreement with the diameters of the smallest BN fullerenes. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.46.-w Structure of nanoscale materials
61.43.Er Other amorphous solids

Temperature tuning of the stop band in transmission spectra of liquid-crystal infiltrated synthetic opal as tunable photonic crystal

Katsumi Yoshino, Yuki Shimoda, Yoshiaki Kawagishi, Keizo Nakayama, and Masanori Ozaki

Appl. Phys. Lett. 75, 932 (1999); http://dx.doi.org/10.1063/1.124558 (3 pages) | Cited 173 times

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Nematic liquid crystals and smectic liquid crystals can be infiltrated into a three-dimensional periodic array of interconnected nanosize voids in opal films prepared by sedimentation of SiO2 spheres of various diameters. The optical stop band in the transmission spectra of opals shifts drastically by the infiltration of liquid crystals. The stop band is also found to shift at the phase transition points with changing temperature. This effect enables the tuning of optical properties of opals as a prototype tunable photonic crystal. This phenomenon can also be used as a measurement method for the refractive index. © 1999 American Institute of Physics.  
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42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.M- Transitions in liquid crystals
78.30.-j Infrared and Raman spectra
78.66.Sq Composite materials

Solid-state amorphization at tetragonal-Ta/Cu interfaces

Kee-Won Kwon, Hoo-Jeong Lee, and Robert Sinclair

Appl. Phys. Lett. 75, 935 (1999); http://dx.doi.org/10.1063/1.124559 (3 pages) | Cited 44 times

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This letter describes the formation of a thin amorphous layer at the tetragonal-Ta/Cu interfaces, which appear in copper metallization structures of microelectronic devices. The disordered layer grows up to 4 nm when annealed at between 400 and 600 °C. Since Ta and Cu are immiscible according to thermodynamic data, this is an unusual observation. A mechanism for the amorphous phase formation is proposed using both physical and chemical considerations. A high content of Cu is detected in the Ta layer up to 5 nm from the interface when annealed at 600 °C. Although the adhesion is promoted by the interface reaction, a sufficiently thick Ta underlayer is recommended for efficient blocking of Cu diffusion. Neither solid-state amorphization nor Cu diffusion into Ta is observed at bcc-Ta/Cu interfaces. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
85.40.Ls Metallization, contacts, interconnects; device isolation

Step decoration during deposition of Co on Ag(001) by ultralow energy ion beams

J. Dekoster, B. Degroote, H. Pattyn, G. Langouche, A. Vantomme, and S. Degroote

Appl. Phys. Lett. 75, 938 (1999); http://dx.doi.org/10.1063/1.124560 (3 pages) | Cited 12 times

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A possibility for decorating atomic steps on single-crystal surfaces by using ultralow energy ion beams is reported. Isotopically pure ion beams are produced by a mass separator and subsequently decelerated by an electrostatic lens. The lens was designed to allow sweeping of the ion beam in order to obtain a uniform deposition over a large area. The preferred sites of single Co atoms on Ag are investigated with in situ scanning tunneling microscopy measurements. A clear indication is found that by increasing the energy of the deposited Co to several electron volts, an enhanced Co decoration of the Ag steps is induced. This technology opens perspectives for an increasing number of elements which can form self-organized nanostructures such as atomic wires on vicinal crystal surfaces. © 1999 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys

Activation volume for antimony diffusion in silicon and implications for strained films

Yuechao Zhao, Michael J. Aziz, Hans-J. Gossmann, Salman Mitha, and David Schiferl

Appl. Phys. Lett. 75, 941 (1999); http://dx.doi.org/10.1063/1.124561 (3 pages) | Cited 14 times

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The diffusivity of Sb in Si is retarded by pressure, characterized at 860 °C by an activation volume of V∗ = +0.07±0.02 times the Si atomic volume. V∗ is close to values inferred from atomistic calculations for a vacancy mechanism. Our results for hydrostatic pressure are used to predict the effect of biaxial strain on Sb diffusion. The prediction matches measured behavior for Sb diffusion in biaxially strained Si and Si–Ge films. This work lends additional support to the predominance of the vacancy mechanism for Sb diffusion and demonstrates the first steps in the development of a capability for predicting the effect of nonhydrostatic stress on diffusion. © 1999 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters

Reactive molecular-beam epitaxy of GaN layers directly on 6H–SiC(0001)

A. Thamm, O. Brandt, Y. Takemura, A. Trampert, and K. H. Ploog

Appl. Phys. Lett. 75, 944 (1999); http://dx.doi.org/10.1063/1.124562 (3 pages) | Cited 30 times

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We investigate the quality of GaN layers directly grown on 6H–SiC(0001) substrates by reactive molecular-beam epitaxy. Despite a pure three-dimensional nucleation, step-flow growth is achieved by in situ adjusting conditions such that the (2×2) reconstruction observed during growth is maximized in intensity. The resulting surface morphology exhibits large terraces separated by mono- and multiatomic steps, and is clearly superior to that obtained by plasma-assisted growth. Furthermore, the structural and optical properties of these layers are comparable to those of layers grown by plasma-assisted molecular-beam epitaxy. © 1999 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Time-resolved Raman spectroscopy of polytetrafluoroethylene under laser-driven shock compression

Kunihiko Wakabayashi, Kazutaka G. Nakamura, Ken-ichi Kondo, and Masatake Yoshida

Appl. Phys. Lett. 75, 947 (1999); http://dx.doi.org/10.1063/1.124563 (3 pages) | Cited 10 times

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Nanosecond time-resolved Raman spectroscopy has been performed to study polymer films, polytetrafluoroethylene, under laser-driven shock compression at about 2.3 GPa. A vibrational line at 1895 cm−1, which is attributed to the symmetric stretching mode of a C2F4 monomer produced by depolymerization, appears under the shock compression, and its intensity increases along the propagation of the shock wave. © 1999 American Institute of Physics.
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78.30.Jw Organic compounds, polymers
61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
78.47.-p Spectroscopy of solid state dynamics
62.50.-p High-pressure effects in solids and liquids
63.50.-x Vibrational states in disordered systems

Metalorganic chemical vapor deposition selective growth and characterization of InGaN quantum dots

J. Wang, M. Nozaki, M. Lachab, Y. Ishikawa, R. S. Qhalid Fareed, T. Wang, M. Hao, and S. Sakai

Appl. Phys. Lett. 75, 950 (1999); http://dx.doi.org/10.1063/1.124564 (3 pages) | Cited 15 times

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InGaN quantum dots (QDs) have been formed by metalorganic chemical vapor deposition selective growth on Si-patterned GaN/sapphire substrates. The QDs were fabricated on GaN plinths grown within nanoscale circular windows opened in the Si mask by both focused ion-beam irradiation and photoassisted wet chemical etching. Using this process, the epitaxial growth of GaN plinths could be achieved on an underlying GaN layer spared from process-induced damage. The optical properties of the InGaN QDs have been investigated by low-temperature cathodoluminescence measurements. Compared to the band-gap emission from a reference sample of InGaN/GaN multiple quantum wells, the evident blueshift of the emission peak from the InGaN QDs was demonstrated. This result suggests that the carriers in the InGaN QDs were three-dimensionally confined. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
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Semi-insulating C-doped GaN and high-mobility AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy

J. B. Webb, H. Tang, S. Rolfe, and J. A. Bardwell

Appl. Phys. Lett. 75, 953 (1999); http://dx.doi.org/10.1063/1.124252 (3 pages) | Cited 58 times

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A method of growing semi-insulating GaN epilayers by ammonia molecular beam epitaxy through intentional doping with carbon is reported. Thick GaN layers of high resistivity are an important element in GaN-based heterostructure field-effect transistors. A methane ion source was used as the carbon dopant source. The cracking of the methane gas by the ion source was found to be the key to the effective incorporation of carbon. High-quality C-doped GaN layers with resistivities greater than 106 Ω cm have been grown with high reproducibility and reliability. AlGaN/GaN heterostructures grown on the C-doped semi-insulating GaN-based layers exhibited a high-mobility two-dimensional electron gas at the heterointerface, with room-temperature mobilities typically between 1000 and 1200 cm2/V s, and liquid-nitrogen-temperature mobilities up to 5660 cm2/V s. The carrier density was almost constant, with less than 3% change over the measured temperature range. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.uj III-V and II-VI semiconductors

Buried single CdTe/CdMnTe quantum dots realized by focused ion beam lithography

G. Bacher, T. Kümmell, D. Eisert, A. Forchel, B. König, W. Ossau, C. R. Becker, and G. Landwehr

Appl. Phys. Lett. 75, 956 (1999); http://dx.doi.org/10.1063/1.124565 (3 pages) | Cited 18 times

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Buried single CdTe/CdMnTe quantum dots are realized by implantation-induced intermixing using a focused 100 keV Ga+ ion beam. For an implantation dose of 5×1013 cm−2 and an annealing temperature of 390 °C, a lateral potential depth of about 65 meV is obtained. By means of photoluminescence spectroscopy, the formation of zero-dimensional multiexcitons in single quantum dots is investigated, yielding a biexciton binding energy of about 3.5 meV. In addition, the occurrence of an excited biexciton transition in the photoluminescence spectrum gives clear evidence of a suppressed exciton spin-flip process in quantum dots. © 1999 American Institute of Physics.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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