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14 Sep 1998

Volume 73, Issue 11, pp. 1457-1597

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Trap states of tris-8-(hydroxyquinoline) aluminum and naphthyl-substituted benzidine derivative using thermally stimulated luminescence

E. W. Forsythe, D. C. Morton, C. W. Tang, and Yongli Gao

Appl. Phys. Lett. 73, 1457 (1998); http://dx.doi.org/10.1063/1.122173 (3 pages) | Cited 49 times

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The bulk trap state properties of a naphthyl-substituted benzidine derivative (NPB) and tris-8-(hydroxyquinoline) aluminum (Alq3) have been measured using thermally stimulated luminescence (TSL). The TSL spectra for both organic materials show significant trap distributions over the temperature range from 8 to 300 K. Using a general order TSL expression, the four peaks in NPB were modeled with trap states centered from 0.20 to 0.05 eV. Alq3 has three TSL peaks over the temperature range, with the peak at 156 K modeled as a distribution of trap states from 0.25 to 0.13 eV. For both materials, the trapping mechanism involves a combination of first and second order emission. NPB and Alq3 have trap states sufficiently deep to influence the carrier transport and recombination process in bilayer organic based light emitting. © 1998 American Institute of Physics.
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78.60.Kn Thermoluminescence
71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Light emission from individual self-assembled InAs/GaAs quantum dots excited by tunneling current injection

K. Yamanaka, K. Suzuki, S. Ishida, and Y. Arakawa

Appl. Phys. Lett. 73, 1460 (1998); http://dx.doi.org/10.1063/1.122174 (3 pages) | Cited 17 times

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We report emission from individual quantum dots excited by tunneling current injection using a scanning tunneling microscope (STM). By scanning the STM tip above the self-assembled InAs quantum dots, a spatially resolved scanning tunneling luminescence (STL) image was measured, which contained a fluorescent circular region with a diameter of 50 nm originating from a single InAs quantum dot. It was found that the spatial resolution of the STL system was about 40 nm, which is mainly due to lateral diffusion of holes injected into a GaAs capping layer grown at low temperature (480 °C). We also obtained STL spectra with a sharp single luminescent peak from a single InAs quantum dot. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Kr excimers produced by soft x rays emitted from a laser-produced plasma

Shoichi Kubodera, Masaki Ikeda, Junji Kawanaka, and Wataru Sasaki

Appl. Phys. Lett. 73, 1463 (1998); http://dx.doi.org/10.1063/1.122175 (3 pages) | Cited 3 times

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We have demonstrated an excitation method to produce Kr2∗ by using soft x rays emitted from a laser-produced plasma. We have found that Kr2+ ions were directly produced by photoionization of Kr atoms by soft x rays. The behavior of Kr2∗ emission was similar to that of Kr2+, indicating fast relaxation processes to produce Kr2∗ from Kr2+ during the plasma producing laser pulse. Numerical results based on a photoionization model of Kr reproduced the experimental results, which verified the production of Kr2∗ initiated by the photoionization of Kr. © 1998 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Photorefractive correlation filtering of time-varying laser speckles for vibration monitoring

Alexei A. Kamshilin, Erik Raita, Kimmo Paivasaari, Timo Jaaskelainen, and Yuri N. Kulchin

Appl. Phys. Lett. 73, 1466 (1998); http://dx.doi.org/10.1063/1.122216 (3 pages) | Cited 3 times

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We proposed and experimentally studied a technique of vibration object monitoring. The technique is based on self-diffraction of the speckle pattern on the adaptive correlation filter recorded in photorefractive Bi12TiO20 crystal. This filter is recorded owing to the light-induced scattering known as fanning effect. The proposed technique is as sensitive as interferometric systems and it is very simple for implementation: neither reference nor readout beam is needed for operation. It is shown that the system has a linear response on the lateral displacement of the object surface and its dynamic range can be easily varied depending on experimental conditions. © 1998 American Institute of Physics.
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42.30.Ms Speckle and moiré patterns
42.40.Kw Holographic interferometry; other holographic techniques
42.79.Ci Filters, zone plates, and polarizers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
07.60.Ly Interferometers
42.40.Ht Hologram recording and readout methods
42.40.Eq Holographic optical elements; holographic gratings
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Enhanced sensitivity near-field scanning optical microscopy at high spatial resolution

H. F. Hamann, A. Gallagher, and D. J. Nesbitt

Appl. Phys. Lett. 73, 1469 (1998); http://dx.doi.org/10.1063/1.122176 (3 pages) | Cited 50 times

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An apertureless near-field optical-imaging method is presented that achieves high spatial resolution as well as a ∼ 4000-fold increase in detection sensitivity, by exploiting the highly localized enhanced near-field interactions between the sample (e.g., Au nanospheres) and a sharp atomic force microscope tip under evanescent laser field illumination. This represents a general method for optical imaging at ⩽ 2 nm spatial resolution, and is applicable to both resonant (i.e., scattering) as well as nonresonant (i.e., fluorescence, Raman, etc.) spectroscopic methods. © 1998 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes

The infrared optical functions of AlxGa1−xN determined by reflectance spectroscopy

G. Yu, H. Ishikawa, M. Umeno, T. Egawa, J. Watanabe, T. Soga, and T. Jimbo

Appl. Phys. Lett. 73, 1472 (1998); http://dx.doi.org/10.1063/1.122177 (3 pages) | Cited 30 times

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Infrared reflectivity measurements have been carried out on samples with structures of GaN/sapphire and AlxGa1−xN/GaN/sapphire as well as sapphire substrates. Analyses of the reflectance data of sapphire using the Kramers–Kronig technique and fitting of the reflectance spectra of GaN and AlxGa1−xN samples using analytical expressions have been made. The high-frequency dielectric constant ϵ∞ and the transverse phonon frequency ωTO, are found to vary from 5.15 to 4.2 and from 559.7 to 586.4 cm−1, respectively, when the composition x is varied from 0 to 0.35 at room temperature. The E2 mode, which arises from the disordered state of the alloys, has been observed in the reflectivity spectrum of AlxGa1−xN, and the intensity of the peak is enhanced by increasing the Al content. © 1998 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)
78.20.-e Optical properties of bulk materials and thin films
78.30.Fs III-V and II-VI semiconductors

Tunnel-junction-connected distributed-feedback vertical-cavity surface-emitting laser

A. N. Korshak, Z. S. Gribnikov, and V. V. Mitin

Appl. Phys. Lett. 73, 1475 (1998); http://dx.doi.org/10.1063/1.122217 (3 pages) | Cited 3 times

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An injection distributed-feedback vertical-cavity surface-emitting laser (VCSEL) with tunnel junctions served as quasi-Ohmic intercontacts (tunnel-junction-connected distributed-feedback VCSEL) is proposed. A periodic structure of vertically stacked double-heterostructure laser diodes connected by low-resistance tunnel junctions forms a vertical distributed-feedback (DFB) laser medium. To minimize the threshold, the DFB structure is placed in a Fabry–Perot cavity designed to match gain layers with the maximums of the optical mode, and the tunnel junctions—with its minimums. The passive regions with tunnel junctions provide effective vertical injection into each active region of this multiple-active-region laser. This DFB VCSEL is expected to have an improved performance, specifically, reduced threshold current and heightened output power. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Enhancement of the third-order nonlinear optical response of quantum wells in a semiconductor microcavity

Hajime Ishihara and Kikuo Cho

Appl. Phys. Lett. 73, 1478 (1998); http://dx.doi.org/10.1063/1.122178 (3 pages) | Cited 5 times

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We discuss the enhancement effect of the third-order nonlinear response of excitons coupled with cavity modes, on the basis of a self-consistent calculation of response field and induced polarization. It is shown that a single framework is enough to describe the spectral features of nonlinear spectra in both strong and weak coupling regimes, where the splitting of coupled modes (cavity polaritons) in linear response is larger and smaller, respectively, than the widths. In the latter regime, the nonlinear signal is strongest at the bare excitonic resonance, and its enhancement due to the cavity effect is remarkable. In the former regime, on the other hand, the nonlinear signal appears at the energy positions of the coupled modes, whose spectral shape represents the reduction of normal-mode splitting due to the nonlinear effect. © 1998 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.20.At Surface states, band structure, electron density of states
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Decay of ultraviolet-induced optical absorption in Ge-doped SiO2 glass

Motoshi Ohama, Takumi Fujiwara, and Akira J. Ikushima

Appl. Phys. Lett. 73, 1481 (1998); http://dx.doi.org/10.1063/1.122179 (3 pages) | Cited 4 times

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We report quantitative measurements on the decay of optical absorption at various elevated temperatures in ultraviolet (UV)-irradiated SiO2 glasses doped with Ge. From the Arrhenius plots of decay time constants, the activation energy of the Ge E′ center in the UV-irradiated glasses has been determined to be 2.4±0.3 eV, while the reported activation energy of Ge E′ decay in UV-poled glasses is 0.4±0.1 eV. The present experimental results strongly suggest that the decay process of the Ge E′ center induced in UV-irradiated glasses is quite different from that in UV-poled glasses. © 1998 American Institute of Physics.  
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78.40.Ha Other nonmetallic inorganics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators

Optical implementation of the wavelet transform by using a bacteriorhodopsin film as an optically addressed spatial light modulator

Joby Joseph, F. J. Aranda, D. V. G. L. N. Rao, B. S. DeCristofano, B. R. Kimball, and M. Nakashima

Appl. Phys. Lett. 73, 1484 (1998); http://dx.doi.org/10.1063/1.122180 (3 pages) | Cited 5 times

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An optical system utilizing the photoinduced dichroism in a bacteriorhodopsin film has been demonstrated for the optical implementation of wavelet transforms. The dichroism, induced by the image of a wavelet filter on a bacteriorhodopsin film leads to polarization rotation of the Fourier components of an image. The polarization-rotated Fourier components of an input scene are analyzed with a polarizer to give the wavelet transform components. The dichroism is induced with beams whose profiles are determined by wavelet filters in order to perform the optical wavelet transform. © 1998 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.20.Fm Birefringence
42.79.Ci Filters, zone plates, and polarizers
42.30.Kq Fourier optics
87.15.M- Spectra of biomolecules
78.66.Qn Polymers; organic compounds

Multicolored light emitters on silicon substrates

Supratik Guha and Nestor A. Bojarczuk

Appl. Phys. Lett. 73, 1487 (1998); http://dx.doi.org/10.1063/1.122181 (3 pages) | Cited 42 times

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We demonstrate the operation of multicolored light emitting diodes (LEDs) on a silicon wafer using ultraviolet/violet GaN LEDs grown by molecular beam epitaxy on Si(111) in conjunction with organic dye based color converters. These organic converters, applied on top of the nitride diodes, absorb the nitride LED electroluminescence at ∼360 nm, and fluoresce in the green (∼530 nm), and orange (∼600 nm). In this fashion, multicolored light emitters may be made to operate side by side and monolithically on the same Si wafer in an approach that may be attractive for miniature GaN based full color displays. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.79.Nv Optical frequency converters
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

High-speed photorefractive polymer composites

D. Wright, M. A. Díaz-García, J. D. Casperson, M. DeClue, W. E. Moerner, and R. J. Twieg

Appl. Phys. Lett. 73, 1490 (1998); http://dx.doi.org/10.1063/1.122182 (3 pages) | Cited 94 times

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Two photorefractive polymer composites are presented that exhibit the fastest response times reported to date by an order of magnitude (τg ≈ 5 ms at 1 W/cm2), while maintaining large gain coefficients (Γ ≈ 230 and 130 cm−1). These materials show promise for video-rate optical processing applications. The factors limiting the photorefractive speed in these materials are investigated. © 1998 American Institute of Physics.
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42.70.Jk Polymers and organics
78.20.-e Optical properties of bulk materials and thin films
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Edge emission observed in heavily boron-doped diamond films epitaxially grown on platinum

Yoshihiro Yokota, Takeshi Tachibana, Koichi Miyata, Koji Kobashi, Akimitsu Hatta, Toshimichi Ito, Akio Hiraki, and Yoshihiro Shintani

Appl. Phys. Lett. 73, 1493 (1998); http://dx.doi.org/10.1063/1.122183 (3 pages) | Cited 3 times

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Cathodoluminescence (CL) spectra of diamond films epitaxially grown on single crystal platinum (111) have been investigated at room temperature and 89 K. It was found that the CL spectra of the heavily boron-doped (>3×1020 cm−3) diamond films of more than 16 μm thickness consist only of a near-edge emission at 248±1 nm (5.00±0.02 eV), while any mid-gap emissions are absent. That result suggests that few defects are in the films. It was also found that the temperature dependence of the 248 nm band is very unique, since its intensity increases as temperature increases. The mechanism of the 248 nm band seems to involve quasi-direct transition. © 1998 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Db Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors

High-temperature optically pumped lasing in ZnMgSSe/ZnSe heterostructures grown by metalorganic vapor phase epitaxy

A. L. Gurskii, I. P. Marko, E. V. Lutsenko, G. P. Yablonskii, H. Kalisch, H. Hamadeh, and M. Heuken

Appl. Phys. Lett. 73, 1496 (1998); http://dx.doi.org/10.1063/1.122184 (3 pages) | Cited 3 times

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Lasing and optical properties of ZnMgSSe/ZnSe-, ZnMgSSe/ZnSSe/ZnSe-, and ZnMgSSe/ZnMgSSe/ZnSe-based single- and multiple-quantum-well heterostructures grown by metalorganic vapor phase epitaxy were studied, and the characteristics were found to depend on the excitation intensity Iexc, temperature, and well width. Laser action under transverse optical pumping was achieved only for well widths Lz ≥ 4 nm and optical confinement factors Γ>0.04. In separate confinement heterostructures, lasing with the lowest threshold (Ithr = 10–30 kW/cm2 at T = 78 K) was achieved and device characteristics were studied up to T = 577 K. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Theory of a self-assembled quantum-dot semiconductor laser with Auger carrier capture: Quantum efficiency and nonlinear gain

A. V. Uskov, Y. Boucher, J. Le Bihan, and J. McInerney

Appl. Phys. Lett. 73, 1499 (1998); http://dx.doi.org/10.1063/1.122185 (3 pages) | Cited 22 times

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We analyze a self-assembled quantum-dot laser where lasing levels are pumped purely through Auger carrier capture. Analysis shows that Auger carrier capture and Auger transport of carriers between quantum dots can provide effective laser pumping and fast modulation at least up to 10 GHz. Auger carrier transport decreases spectral hole burning, which together with dot-barrier hole burning can damp relaxation oscillations. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Ah General laser theory
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Molecular dynamics simulation of enhanced oxygen ion diffusion in strained yttria-stabilized zirconia

Ken Suzuki, Momoji Kubo, Yasunori Oumi, Ryuji Miura, Hiromitsu Takaba, Adil Fahmi, Abhijit Chatterjee, Kazuo Teraishi, and Akira Miyamoto

Appl. Phys. Lett. 73, 1502 (1998); http://dx.doi.org/10.1063/1.122186 (3 pages) | Cited 16 times

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The application of strain to yttria-stabilized zirconia (YSZ), which can be realized by sandwiching a thin YSZ film epitaxially between layers of a material with larger lattice constants, is proposed as a means to enhance oxygen ion mobility. The possible mechanism of such an enhancement was investigated by molecular dynamics using a CeO2–YSZ superlattice. The calculated diffusion coefficient of oxygen ions in the superlattice is some 1.7 times higher than in YSZ alone due to a decreased activation barrier from the strain of the YSZ structure. © 1998 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals

Manipulation of Ag nanoparticles utilizing noncontact atomic force microscopy

M. Martin, L. Roschier, P. Hakonen, Ü. Parts, M. Paalanen, B. Schleicher, and E. I. Kauppinen

Appl. Phys. Lett. 73, 1505 (1998); http://dx.doi.org/10.1063/1.122187 (3 pages) | Cited 19 times

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We have developed a scheme to manipulate metallic aerosol particles on silicon dioxide substrates using an atomic force microscope. The method utilizes the noncontact mode both for locating and moving nanoparticles of size 10–100 nm. The main advantage of our technique is the possibility of “seeing” the moving particle in real time. Our method avoids well sticking problems that typically hamper the manipulation in the contact mode. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
82.70.Rr Aerosols and foams
81.07.-b Nanoscale materials and structures: fabrication and characterization

Exploiting the properties of carbon nanotubes for nanolithography

Hongjie Dai, Nathan Franklin, and Jie Han

Appl. Phys. Lett. 73, 1508 (1998); http://dx.doi.org/10.1063/1.122188 (3 pages) | Cited 103 times

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Carbon nanotube tips are explored in fabricating oxide nanostructures on silicon surfaces with an atomic force microscope. Nanotubes can write nanostructures at speeds up to 0.5 mm/s over large surface areas, and present a solution to the long-standing tip-wear problem. Experimental and theoretical work find that nanotube tips are impervious to high compressive and lateral forces and breakdown in high electric fields. A “cleaving” method is developed to reproducibly obtain dome-closed multi-walled nanotube tips with suitable length. Nanotube materials could become key elements for future miniaturization applications. © 1998 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.79.Lh Atomic force microscopes

Optical detection of crystallographic domains in zinc-blende crystals

G. Mohs, R. Shimano, T. Kise, M. Shirane, M. Kuwata-Gonokami, K. Ohkawa, S. Dhanjal, Y. Svirko, and N. Zheludev

Appl. Phys. Lett. 73, 1511 (1998); http://dx.doi.org/10.1063/1.122189 (3 pages)

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We introduce an experimental technique which allows the characterization of domains in nonmagnetic cubic crystals of the zinc-blende type. The technique exploits the optical anisotropy of cubic crystals near an excitonic resonance which translates to a dependence of the reflected light polarization on crystal orientation. We demonstrate sub 10 μm domains on the [110] surface of a high quality, homoepitaxially grown ZnSe film. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors

Deposition of highly crosslinked fluorinated amorphous carbon film and structural evolution during thermal annealing

Hongning Yang, Douglas J. Tweet, Yanjun Ma, and Tue Nguyen

Appl. Phys. Lett. 73, 1514 (1998); http://dx.doi.org/10.1063/1.122190 (3 pages) | Cited 46 times

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Highly crosslinked fluorinated amorphous carbon films are obtained by increasing deposition temperature, enhancing ion bombardment, and fine tuning the fluorine-to-carbon ratio. The as-deposited films undergo significant mechanical, chemical, and electrical changes after thermal annealing. Most importantly, these changes occur only at the initial stage of annealing. After the thermal treatment, the films tend to be thermally stable and retain reasonably good electrical properties for use as a low-k dielectric. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing

Intermixing at the tantalum oxide/silicon interface in gate dielectric structures

G. B. Alers, D. J. Werder, Y. Chabal, H. C. Lu, E. P. Gusev, E. Garfunkel, T. Gustafsson, and R. S. Urdahl

Appl. Phys. Lett. 73, 1517 (1998); http://dx.doi.org/10.1063/1.122191 (3 pages) | Cited 139 times

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Metal oxides with high dielectric constants have the potential to extend scaling of transistor gate capacitance beyond that of ultrathin silicon dioxide. However, during deposition of most metal oxides on silicon, an interfacial region of SiOx can form that limits the specific capacitance of the gate structure. We have examined the composition of this layer using high-resolution depth profiling of medium ion energy scattering combined with infrared spectroscopy and transmission electron microscopy. We find that the interfacial region is not pure SiO2, but is a complex depth-dependent ternary oxide of Si–Tax–Oy with a dielectric constant at least twice that of pure SiO2 as inferred from electrical measurements. High-temperature annealing crystallizes the Ta2O5 film and converts the composite oxide to a more pure SiO2 layer with a lower capacitance density. Using low postanneal temperatures, a stable composite oxide structure can be obtained with good electrical properties and an effective SiO2 thickness of less than 2 nm with ∼10 nm of composite oxide. © 1998 American Institute of Physics.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.30.-j Infrared and Raman spectra
61.72.Cc Kinetics of defect formation and annealing
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Comparison between optical techniques for the measurement of the surface electric field in (100) oriented GaAs

Z. Yang, Y. H. Chen, and Yuqi Wong

Appl. Phys. Lett. 73, 1520 (1998); http://dx.doi.org/10.1063/1.122192 (3 pages) | Cited 5 times

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Three optical spectroscopic techniques commonly used for the measurement of the surface electric field (SEF) of semiconductors, namely photoreflectance (PR) near the E0 energy and near the E1 energy, and the linear electro-optic (LEO) effect of reflectance difference spectroscopy near the E1 energy, are compared on a series of (100) oriented GaAs layered structures. The LEO strength is found to be linearly proportional to the SEF obtained from the PR oscillation period near the E0 energy for samples with a single space charge region in which the field is uniform over the light penetration depth near E1( ∼ 20 nm). The LEO strength remains proportional to the SEF for samples with multiple space charge regions while the PR period near E0 no longer reflects the true SEF. The SEF value estimated from the line width of PR near the E1 energy is quite unreliable because both the electric field and the impurity scattering broaden the line. © 1998 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.20.-e Optical properties of bulk materials and thin films
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Cathodoluminescence study of degradation in ZnSe-based semiconductor laser diodes

A. Toda, K. Nakano, and A. Ishibashi

Appl. Phys. Lett. 73, 1523 (1998); http://dx.doi.org/10.1063/1.122193 (3 pages) | Cited 16 times

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After continuous-wave operation of ZnSe-based semiconductor laser diodes, the degradation of these devices was investigated using cathodoluminescence imaging and spectroscopy. Inside the stripe region, i.e., the carrier injection area, there were several dots in which the peak wavelength of emission from a ZnCdSe strained quantum well (QW) shifted with time to a shorter wavelength (blueshift). We consider that the blueshift is due to Cd/Zn interdiffusion. This interdiffusion is enhanced by the electron–hole recombination process (recombination enhanced interdiffusion). Furthermore, there were dark line defects (DLDs) in the 〈100〉 direction, outside the stripe region and running away from the dots, having emission with a blueshift. The peak wavelength of emission from the QW in the DLDs shifted to a longer wavelength (redshift). We consider that the redshift is due to the relaxation of strain in the QW by existing defects, which may originate in the blueshift dots and move outside the stripe region. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors
68.35.Fx Diffusion; interface formation
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Optimization of hydrogenated amorphous silicon p–i–n solar cells with two-step i layers guided by real-time spectroscopic ellipsometry

Joohyun Koh, Yeeheng Lee, H. Fujiwara, C. R. Wronski, and R. W. Collins

Appl. Phys. Lett. 73, 1526 (1998); http://dx.doi.org/10.1063/1.122194 (3 pages) | Cited 89 times

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Hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell performance has been optimized using a two-step i-layer growth process. This effort has been guided by real-time spectroscopic ellipsometry (RTSE) studies of the nucleation and growth of a-Si:H films by plasma-enhanced chemical vapor deposition at 200 °C using a variable H2-dilution gas flow ratio R = [H2]/[SiH4]. RTSE studies during film growth with R>15 reveal a transition from the amorphous to microcrystalline (a→μc) phase at a critical thickness that decreases with increasing R. From such results, the optimum two-step process was designed such that the initial stage of the i layer (∼200 Å) is deposited at much higher R than the bulk to ensure that the film remains within the amorphous side of the a→μc phase boundary, yet as close as possible to this boundary at low i-layer thicknesses. © 1998 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology

Arsenic flux dependence of incorporation of excess arsenic in molecular beam epitaxy of GaAs at low temperature

A. Suda and N. Otsuka

Appl. Phys. Lett. 73, 1529 (1998); http://dx.doi.org/10.1063/1.122195 (3 pages) | Cited 14 times

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Incorporation of excess As in GaAs layers grown by molecular beam epitaxy was studied by varying As fluxes for four different substrate temperatures, 210, 240, 270, and 290 °C. Concentrations of excess As in GaAs layers were estimated by measuring increases of lattice spacings with x-ray diffraction, and the substrate surface temperature was monitored by using a quartz rod connected to an infrared pyrometer with its end placed in the vicinity of the substrate surface. Nearly stoichiometric GaAs layers without any detectable increase of the lattice spacing are grown at all substrate temperatures under the As atom flux equal to the Ga atom flux. With a slight increase of the As flux from the above stoichiometric condition, the concentration of excess As sharply increases for all substrate temperatures. For the substrate temperature of 210 °C, the concentration of excess As is saturated in the range of As atom fluxes more than three times the Ga atom flux, while similar tendencies are observed for other substrate temperatures. The incorporation process of excess As is discussed on the basis of these results. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Nq Composition and phase identification
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