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25 Jan 1999

Volume 74, Issue 4, pp. 483-629

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Low-threshold high-quantum-efficiency laterally gain-coupled InGaAs/AlGaAs distributed feedback lasers

M. Kamp, J. Hofmann, A. Forchel, F. Schäfer, and J. P. Reithmaier

Appl. Phys. Lett. 74, 483 (1999); http://dx.doi.org/10.1063/1.123164 (3 pages) | Cited 40 times

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We have developed gain-coupled lasers based on metal gratings patterned laterally to the laser ridge. For narrow ridge waveguides, the evanescent field of the laser mode couples to the grating. The fabrication requires no overgrowth steps and can be applied to all material systems. Ridge-waveguide gain-coupled lasers with threshold current densities of 600 A/cm2 were obtained from InGaAs/AlGaAs GRINSCH structures. The continuous wave threshold currents are around 9 mA for a cavity with 600 μm length and 2.5 μm width. Monomode emission up to output power levels of 64 mW and sidemode suppression ratios of over 45 dB have been obtained. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.79.Ry Gradient-index (GRIN) devices
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Experimental demonstration of photonic crystal based waveguides

B. Temelkuran and E. Ozbay

Appl. Phys. Lett. 74, 486 (1999); http://dx.doi.org/10.1063/1.123163 (3 pages) | Cited 51 times

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We report the experimental demonstration of waveguides built around layer-by-layer photonic crystals. An air gap introduced between two photonic crystal walls was used as the waveguide. We observed full (100%) transmission of the electromagnetic (EM) waves through these planar waveguide structures within the frequency range of the photonic band gap. The dispersion relations obtained from the experiment were in good agreement with the predictions of our waveguide model. We also observed 35% transmission for the EM waves traveling through a sharp bend in an L-shaped waveguide carved inside the photonic crystal. © 1999 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.50.-p Quantum optics
42.70.Qs Photonic bandgap materials

Carrier nonuniformity effects on the internal efficiency of multiquantum-well lasers

Joachim Piprek, Patrick Abraham, and John E. Bowers

Appl. Phys. Lett. 74, 489 (1999); http://dx.doi.org/10.1063/1.123165 (3 pages) | Cited 21 times

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We investigate quantum efficiency limitations in InGaAsP/InP multiquantum-well (MQW) laser diodes emitting at 1.5 μm. At room temperature, the internal differential efficiency above threshold is found to be reduced mainly by increasing Auger recombination and spontaneous emission within the quantum wells. These carrier loss increments are commonly assumed negligible due to MQW carrier density clamping. Even with clamped average carrier density, increasing nonuniformity of the quantum well carrier population leads to enhanced losses. We analyze these loss enhancements using an advanced laser simulation software. Excellent agreement between measurements and simulations is obtained. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Waveguide fabrication and high-speed in-line intensity modulation in 4-N,N-4′-dimethylamino-4′-N′-methyl-stilbazolium tosylate

F. Pan, K. McCallion, and M. Chiappetta

Appl. Phys. Lett. 74, 492 (1999); http://dx.doi.org/10.1063/1.123956 (3 pages) | Cited 22 times

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We report the formation of thin-film waveguides of organic crystals by precision optical polishing and the fabrication of an electro-optic intensity modulation device based on a thin-film waveguide of N,N-4′-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST®) as an overlay on a side-polished fiber (SPF). Successful fabrication of single-crystal DAST® waveguides with thicknesses in the 20–25 μm range have been produced. The waveguides were investigated via an evanescent coupling technique using side-polished fibers rather than traditional end-firing methods. Surface quality is believed to have been sufficient for low-loss propagation. Electrodes were added to the SPF/DAST® overlay architecture and intensity modulation observed out to 18 GHz. The device frequency response is believed to extend beyond 100 GHz under optimum conditions. © 1999 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.79.Hp Optical processors, correlators, and modulators
42.70.Jk Polymers and organics

Thickness dependence of second-harmonic generation in thin films fabricated from ionically self-assembled monolayers

J. R. Heflin, C. Figura, D. Marciu, Y. Liu, and R. O. Claus

Appl. Phys. Lett. 74, 495 (1999); http://dx.doi.org/10.1063/1.123166 (3 pages) | Cited 32 times

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An ionically self-assembled monolayer (ISAM) technique for thin-film deposition has been employed to fabricate materials possessing the noncentrosymmetry that is requisite for a second-order, χ(2), nonlinear optical response. As a result of the ionic attraction between successive layers, the ISAM χ(2) films self-assemble into a noncentrosymmetric structure that has exhibited no measurable decay of χ(2) at room temperature over a period of more than one year. The second-harmonic intensity of the films exhibits the expected quadratic dependence on film thickness up to at least 100 bilayers, corresponding to a film thickness of 120 nm. The polarization dependence of the second-harmonic generation yields a value of 35° for the average tilt angle of the nonlinear optical chromophores away from the surface normal. © 1999 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Wc Optical coatings

CdSe fractional-monolayer active region of molecular beam epitaxy grown green ZnSe-based lasers

S. V. Ivanov, A. A. Toropov, S. V. Sorokin, T. V. Shubina, I. V. Sedova, A. A. Sitnikova, P. S. Kop’ev, Zh. I. Alferov, H.-J. Lugauer, G. Reuscher, M. Keim, F. Fischer, A. Waag, and G. Landwehr

Appl. Phys. Lett. 74, 498 (1999); http://dx.doi.org/10.1063/1.123167 (3 pages) | Cited 36 times

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This letter reports on the self-organized growth of nanoscale dot-like CdSe-based islands during molecular beam epitaxy of CdSe/ZnSe nanostructures with a CdSe thickness between 0.75 and 3.0 monolayers. An increase in the nominal CdSe thickness results in a higher density of islands (up to 2×1010 cm−2) and is accompanied by dramatic enhancement of the photoluminescence efficiency. The density of large relaxed islands appears to saturate at a value of (3–4)×109 cm−2. Room temperature (Zn, Mg)(S, Se)-based optically pumped lasers with an extremely low threshold (less than 4 kW/cm2), as well as (Be, Mg, Zn)Se-based injection laser diodes using a single (2.5–2.8) monolayer thick CdSe active region, both demonstrating significantly enhanced degradation stability, have been fabricated and studied. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
42.60.By Design of specific laser systems
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
81.07.-b Nanoscale materials and structures: fabrication and characterization

Near-field photolithography with a solid immersion lens

L. P. Ghislain, V. B. Elings, K. B. Crozier, S. R. Manalis, S. C. Minne, K. Wilder, G. S. Kino, and C. F. Quate

Appl. Phys. Lett. 74, 501 (1999); http://dx.doi.org/10.1063/1.123168 (3 pages) | Cited 54 times

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We have exposed 190 nm lines in photoresist by focusing a laser beam (λ=442 nm) in a solid immersion lens (SIL) that is mounted on a flexible cantilever and scanned by a modified commercial atomic force microscope. The scan rate was 1 cm/s, which is several orders of magnitude faster than typical reports of near-field lithography using tapered optical fibers. The enhanced speed is a result of the high optical efficiency (about 10−1) of the SIL. Once exposed with the SIL, the photoresist was developed and the pattern was transferred to the silicon substrate by plasma etching. © 1999 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Bh Lenses, prisms and mirrors
07.79.Lh Atomic force microscopes
07.79.Fc Near-field scanning optical microscopes

Active reflection via a phase-insensitive quadratic nonlinear interaction within a microcavity

Crina Cojocaru, Jordi Martorell, R. Vilaseca, J. Trull, and Eugenio Fazio

Appl. Phys. Lett. 74, 504 (1999); http://dx.doi.org/10.1063/1.123169 (3 pages) | Cited 8 times

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The reflectivity of a microcavity filled with a quadratic nonlinear material is shown to be actively changed by the interaction of two waves. Within this microcavity, the reflection coefficient of a weak wave at the fundamental frequency is changed from almost 0% to a value in the vicinity of 100% by the simultaneous incidence of an intense wave at the second-harmonic frequency. This change in reflectivity is shown to be in a large degree insensitive to the input phase difference between the two waves. © 1999 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.Gy Edge and boundary effects; reflection and refraction

High contrast, ultrafast optically addressed ultraviolet light modulator based upon optical anisotropy in ZnO films grown on R-plane sapphire

M. Wraback, H. Shen, S. Liang, C. R. Gorla, and Y. Lu

Appl. Phys. Lett. 74, 507 (1999); http://dx.doi.org/10.1063/1.124223 (3 pages) | Cited 76 times

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An optically addressed ultraviolet light modulator has been demonstrated which exploits the optical anisotropy in a ZnO film epitaxially grown on (0112) sapphire. This device achieves both high contrast and high speed by exploiting the anisotropic bleaching of the anisotropic absorption and concomitant ultrafast polarization rotation near the lowest exciton resonances produced by femtosecond ultraviolet pulses. The resultant modulation is characterized by a contrast ratio of 70:1, corresponding to a dynamic polarization rotation of 12°, and it decays to a quasiequilibrium value within 100 ps. © 1999 American Institute of Physics.  
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42.79.Hp Optical processors, correlators, and modulators
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Hf II-VI semiconductors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.40.Fy Semiconductors

Generation of dark pulse trains from continuous-wave light using cross-phase modulation in optical fibers

Wen-hua Cao, Shenping Li, and Kam-tai Chan

Appl. Phys. Lett. 74, 510 (1999); http://dx.doi.org/10.1063/1.123170 (3 pages) | Cited 2 times

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A technique for the generation of dark pulse trains from continuous-wave (cw) light is presented. It consists of co-propagating a cw signal with intense pump pulses in an optical fiber where both the signal and the pump experience normal group-velocity dispersion. The pump imposes a positive frequency chirp on the signal through cross-phase modulation while normal dispersion tends to chip out the signal energy in the chirped region, thus leading to the generation of a dark pulse train with a repetition rate identical to that of the pump. A train of 30.3 ps dark pulses has been observed when using 31.7 ps pump pulses from an actively mode-locked fiber ring laser. The experimental results agree well with numerical simulations. © 1999 American Institute of Physics.
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42.81.Dp Propagation, scattering, and losses; solitons
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
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Time-resolved photoluminescence studies of an ionized donor-bound exciton in GaN

R. A. Mair, J. Li, S. K. Duan, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 74, 513 (1999); http://dx.doi.org/10.1063/1.123171 (3 pages) | Cited 17 times

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Time-resolved photoluminescence (PL) spectroscopy has been used to study the radiative recombination of excitons bound to ionized donors in GaN doped with both Mg and Si at concentrations of 5×1018/cm3 and 1.5×1017/cm3, respectively. Low temperature (T ∼ 10K) time-resolved, as well as integrated PL spectra, identify an ionized donor-bound (Si) exciton peak (D+X) approximately 11.5 meV below and a neutral acceptor-bound exciton (A0X) 20.5 meV below the free exciton peak. Rapid decay of the free exciton emission (⩽20 ps) implies that excitons are quickly captured by acceptors and ionized donors. We find the (A0X) emission lifetime is consistent with previous measurements for GaN:Mg epilayers, while the (D+X) lifetime of 160 ps is longer than that of the well studied neutral donor-bound exciton (D0X). The measured (D+X) lifetime, in comparison with (D0X) and (A0X), suggests that the state is stable at low temperature. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.35.Gg Exciton-mediated interactions
71.55.Eq III-V semiconductors

Hydrogen-induced reduction of axial stress in optical fiber cores

Nguyen Hong Ky, H. G. Limberger, R. P. Salathé, F. Cochet, and L. Dong

Appl. Phys. Lett. 74, 516 (1999); http://dx.doi.org/10.1063/1.123172 (3 pages) | Cited 8 times

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Radial distributions of axial stress across B/Ge- and Sn/Ge-codoped core fibers and a Corning standard single-mode fiber were measured before and after hydrogen loading under different conditions. A significant reduction of axial stress in the core of all investigated fibers is observed after hydrogen loading. The stress reduction in the core of hydrogen-loaded fibers is irreversible and depends strongly on the core dopants and the fiber drawing tension. The hydrogen-induced core stress reduction is believed to be related to the reactions between hydrogen and drawing-induced defects in the fiber core. © 1999 American Institute of Physics.
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42.81.Bm Fabrication, cladding, and splicing

Optically induced surface relief phenomena in azobenzene polymers

N. C. R. Holme, L. Nikolova, S. Hvilsted, P. H. Rasmussen, R. H. Berg, and P. S. Ramanujam

Appl. Phys. Lett. 74, 519 (1999); http://dx.doi.org/10.1063/1.123173 (3 pages) | Cited 30 times

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Azobenzene polymers and oligomers show intriguing surface relief features when irradiated with polarized laser light. We show through atomic force microscopic investigation of side-chain azobenzene polymers after irradiation through an amplitude mask that large peaks or trenches result depending on the architecture of the polymer. Extensive mass transport over long distances has been observed, paving the way for easy replication of nanostructures. We also show that it is possible to store microscopic images as topographic features in the polymers just through polarized light irradiation. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
79.20.Ds Laser-beam impact phenomena

Mechanism for interfacial adhesion strength of an ion beam mixed Cu/polyimide with a thin buffer layer

G. S. Chang, K. H. Chae, C. N. Whang, E. Z. Kurmaev, D. A. Zatsepin, R. P. Winarski, D. L. Ederer, A. Moewes, and Y. P. Lee

Appl. Phys. Lett. 74, 522 (1999); http://dx.doi.org/10.1063/1.123174 (3 pages) | Cited 12 times

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A Cu (400 Å)/Al (50 Å)/polyimide system showed larger adhesion strength than that of Cu (400 Å)/polyimide after N2+ ion beam mixing. X-ray emission spectroscopy was performed to elucidate the mechanism of adhesion enhancement of the ion beam mixed Cu (400 Å)/polyimide with a thin Al buffer layer. Cu L2,3 x-ray emission spectra showed the formation of a CuAl2O4 layer which is strongly correlated with the large adhesion strength of a Cu/Al/polyimide. A decrease in adhesion strength at an ion dose higher than 5×1015 cm−2 was also explained by the formation of an amorphous carbon. This was understood by investigating C Kα x-ray emission spectra. The overall spectroscopic results were in accordance with the behavior of quantitative adhesion strength. © 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.Gy Mechanical properties; surface strains
78.70.En X-ray emission spectra and fluorescence
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
68.55.Nq Composition and phase identification

Fabrication of nano-structural arrays by channeling pulsed atomic beams through pulsed-laser standing-waves under off-resonant condition

X. D. Zhu

Appl. Phys. Lett. 74, 525 (1999); http://dx.doi.org/10.1063/1.123175 (3 pages) | Cited 3 times

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We show that it is feasible to produce one- and two-dimensional nano-structure arrays by passing microsecond pulsed atomic beams through microsecond laser standing-wave patterns under completely off-resonant condition. This method enables fabrication of vertically heterogeneous nanostructures such as multilayers with one pulsed laser system. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
42.62.-b Laser applications

The effect of native oxide on epitaxial SiGe from deposited amorphous Ge on Si

Y. H. Wu, W. J. Chen, Albert Chin, and C. Tsai

Appl. Phys. Lett. 74, 528 (1999); http://dx.doi.org/10.1063/1.123176 (3 pages) | Cited 17 times

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We have investigated the effect of native oxide on the epitaxial SiGe from deposited amorphous Ge on Si. Instead of epitaxial growth by molecular beam epitaxy or ultrahigh-vacuum chemical vapor deposition, the SiGe layer is formed by this simple process followed by an annealing step. As observed by transmission electron microscopy, the suppression of native oxide plays an important role to achieve epitaxial SiGe. The SiGe quality degrades with increasing native oxide thickness and becomes polycrystalline with a ∼ 20 Å interfacial native oxide. On the other hand, single crystalline SiGe can be routinely formed from a HF-vapor treated Si surface. © 1999 American Institute of Physics.  
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68.55.-a Thin film structure and morphology
81.05.Hd Other semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.Cc Kinetics of defect formation and annealing
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation

Metastable surface ordering in strain relaxed Si0.5Ge0.5 epitaxial layers grown at high temperature

H. Reichert, S. C. Moss, P. Imperatori, and K. Evans-Lutterodt

Appl. Phys. Lett. 74, 531 (1999); http://dx.doi.org/10.1063/1.123177 (3 pages) | Cited 3 times

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We have studied compositional ordering in the near surface region of 3500 Å thick unstrained Si0.5Ge0.5(001) samples grown by chemical vapor deposition. Measuring asymptotic Bragg scattering along integer and half-integer truncation rods, we found a type of metastable ordering at this surface which is characterized by integer/half-integer reflections along the integer order truncation rods. We show unambiguously that those scattering features originate from a thin layer at the surface. Annealing at 750 °C extinguished these reflections irreversibly, while the reflections of the RS3 bulk structure were not affected. Anomalous scattering at the Ge K edge also confirmed the existence of a new structure in the near surface region. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
68.35.Dv Composition, segregation; defects and impurities
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing

Asymmetric electro-optical response in a liquid crystal cell containing a layer of amorphous tungsten trioxide

G. Strangi, D. E. Lucchetta, E. Cazzanelli, N. Scaramuzza, C. Versacé, and R. Bartolino

Appl. Phys. Lett. 74, 534 (1999); http://dx.doi.org/10.1063/1.123178 (3 pages) | Cited 20 times

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In this work, we present the experimental evidence of a polarity sensitive electro-optic response in a nematic liquid crystal. The liquid crystal cell was made by using a standard sandwich configuration, with one of the indium tin oxide electrodes covered by a thin layer of tungsten trioxide (WO3), deposited by sputtering. The optical response was inhibited when the electrode covered by WO3 film was anodically charged, while the usual optical response occurred under a reverse field. An ionic diffusion process was associated with the establishment of an internal electric field, which inhibited unipolarly the optical switching. © 1999 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.66.Nk Insulators
81.15.Cd Deposition by sputtering

1.5 μm infrared photoluminescence phenomena in Er-doped porous silicon

M. Stepikhova, L. Palmetshofer, W. Jantsch, H. J. von Bardeleben, and N. V. Gaponenko

Appl. Phys. Lett. 74, 537 (1999); http://dx.doi.org/10.1063/1.123179 (3 pages) | Cited 14 times

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We analyze the photoluminescence (PL) in nanoporous Si (po-Si) doped with Er by electrochemical deposition and by spin-on doping. Two kinds of optically active Er centers appear in electrochemically doped po-Si with the main sharp and intense lines at 1.548 and 1.539 μm, respectively. The features characteristic for the spin-on doping method are: intense dislocation-related PL at 1.53 μm and strong luminescent activity of the silica gel used for Er doping. High-temperature PL observed up to 360 K is attributed to Er centers incorporated in the silica-like matrix at the oxidized surface of electrochemically doped po-Si and in erbium-containing silica gel. © 1999 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.55.Mb Porous materials
78.66.Db Elemental semiconductors and insulators
71.55.Cn Elemental semiconductors

Electrical and optical properties of Ge–implanted 4H–SiC

G. Katulka, C. Guedj, J. Kolodzey, R. G. Wilson, C. Swann, M. W. Tsao, and J. Rabolt

Appl. Phys. Lett. 74, 540 (1999); http://dx.doi.org/10.1063/1.123186 (3 pages) | Cited 13 times

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The structural, electronic, and optical properties of single crystalline n-type 4H–SiC implanted with Ge atoms have been investigated through x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Raman spectroscopy, and sheet resistivity measurements. Ge atoms are implanted under the conditions of a 300 keV ion beam energy with a dose of 2×1016 cm−2. X-ray diffraction of the Ge-implanted sample showed broadening of the Bragg peaks. A shoulder on the (0004) reflection indicated an increase in the lattice constant corresponding to substitutional Ge and implantation induced lattice damage, which was repaired through thermal annealing at 1000 °C. The diffraction pattern after annealing indicated improved crystal structure and a peak shift to a lower reflection angle of 35.2°. The composition of Ge detected through XRD was reasonably consistent with RBS measurements that indicated 1.2% Ge in a 1600-Å-thick layer near the SiC surface. Raman spectroscopy also showed fundamental differences in the spectra obtained for the Ge-implanted SiC (SiC:Ge) compared to a pure sample of SiC. Sheet resistivity measurements indicate a higher conductivity in the Ge implant by a factor of 1.94 compared to unimplanted SiC. These results have demonstrated the possibility of substitutional implantation of Ge atoms into the crystalline lattice of 4H–SiC substrates. The change in composition and properties may have numerous electronic device applications including high power, high temperature, optoelectronic, as well as high frequency device structures. © 1999 American Institute of Physics.
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72.80.Jc Other crystalline inorganic semiconductors
61.72.up Other materials
61.82.Fk Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
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Optical characterization of the “E2” deep level in GaN

P. Hacke, P. Ramvall, S. Tanaka, Y. Aoyagi, A. Kuramata, K. Horino, and H. Munekata

Appl. Phys. Lett. 74, 543 (1999); http://dx.doi.org/10.1063/1.123180 (3 pages) | Cited 13 times

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The correspondence between the E2 level ( ∼ Ec−0.55 eV) in n-type GaN undergoing thermoionization and photoionization was established. The optical cross section in the vicinity of the threshold for photoionization of this level was measured by means of capacitance transient spectroscopy. Analysis using the formulation of Chantre yielded the optical activation energy, Eo=0.85 eV, and the Franck–Condon parameter, dFC = 0.30 eV at 90 K. © 1999 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Ek Optical activity

Electronic states at aluminum nitride (0001)-1×1 surfaces

C. I. Wu and A. Kahn

Appl. Phys. Lett. 74, 546 (1999); http://dx.doi.org/10.1063/1.123140 (3 pages) | Cited 22 times

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We investigate the electronic structure of aluminum nitride (0001)-1×1 surfaces via direct and inverse photoemission spectroscopy. Bulk and surface sensitive measurements on clean surfaces and surfaces exposed to oxygen or cesium demonstrate the existence of filled and empty surface states which extend more than 1 eV beyond the valence- and conduction-band edges. The filled states are tentatively associated with Al dangling or back bonds. The measurement of the top of the valence band upon removal of the filled states leads to a determination of an electron affinity equal to 1.9±0.2 eV. The empty surface states are presumed to play a role in the pinning of the Fermi level in the upper part of the gap and are consistent with the anticipated metallicity of the surface. © 1999 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.-g Interactions of particles and radiation with matter
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Degradation of AlGaN during high-temperature annealing monitored by ultraviolet Raman scattering

M. Kuball, F. Demangeot, J. Frandon, M. A. Renucci, H. Sands, D. N. Batchelder, S. Clur, and O. Briot

Appl. Phys. Lett. 74, 549 (1999); http://dx.doi.org/10.1063/1.123141 (3 pages) | Cited 10 times

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We have illustrated the use of ultraviolet (UV) Raman scattering to investigate the thermal stability of AlGaN layers with high-aluminum content. The degradation pathway of Al0.72Ga0.28N was monitored for high-temperature treatments up to 1200 °C. For annealing temperatures higher than 1150 °C, the Al0.72Ga0.28N film decomposes: a low- and a high-aluminum composition AlxGa1−xN phase emerge. At 1100 °C, prior to the Al0.72Ga0.28N decomposition, UV Raman scattering detects the buildup of a large strain in the Al0.72Ga0.28N film. The crystalline quality of Al0.72Ga0.28N is unaffected up to 1000 °C. © 1999 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
61.72.Cc Kinetics of defect formation and annealing
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.55.Cr III-V semiconductors

Annealing conditions for intrinsic CdTe

M. A. Berding

Appl. Phys. Lett. 74, 552 (1999); http://dx.doi.org/10.1063/1.123142 (3 pages) | Cited 23 times

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Equilibrium native defect densities in CdTe are calculated from ab initio methods, and compared with experimental results. We find that CdTe is highly compensated p type under tellurium-saturated conditions, with the cadmium vacancy as the dominant acceptor and the tellurium antisite as the compensating donor. This finding is in agreement with recent experiments that find a much larger deviation from stoichiometry than would be predicted by the electrically active defects. Under cadmium-saturated conditions, cadmium interstitials are predicted to dominate and the material is found to be n type. Native defect concentrations and the corresponding carrier concentrations are predicted as a function of processing conditions, and can serve as a guide to postgrowth anneals to manipulate the conductivity of undoped material for applications in x- and γ-ray spectrometers. Furthermore, we show that by choosing appropriate annealing conditions and extrinsic dopants, one can increase the operating efficiency of nuclear spectrometers by reducing the density of specific native defects that produce midgap trapping states. © 1999 American Institute of Physics.
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71.55.Gs II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.80.Ey III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
72.20.Fr Low-field transport and mobility; piezoresistance
29.40.Wk Solid-state detectors
61.66.Bi Elemental solids
61.66.Dk Alloys

Single-electron capacitance spectroscopy of vertical quantum dots using a single-electron transistor

M. Koltonyuk, D. Berman, N. B. Zhitenev, R. C. Ashoori, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 74, 555 (1999); http://dx.doi.org/10.1063/1.123143 (3 pages) | Cited 7 times

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We have incorporated an aluminum single-electron transistor (SET) directly on top of a vertical quantum dot, enabling the use of the SET as an electrometer that is extremely responsive to the motion of charge into and out of the dot. Charge induced on the SET central island from single-electron additions to the dot modulates the SET output, and we describe two methods for demodulation that permit quantitative extraction of the quantum dot capacitance signal. The two methods produce closely similar results for the determined single-electron capacitance peaks. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.35.Gv Single electron devices
07.68.+m Photography, photographic instruments; xerography
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