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28 Jun 1999

Volume 74, Issue 26, pp. 3921-4070

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Surface-mode lasing from stacked InGaN insertions in a GaN matrix

A. V. Sakharov, W. V. Lundin, I. L. Krestnikov, V. A. Semenov, A. S. Usikov, A. F. Tsatsul’nikov, Yu. G. Musikhin, M. V. Baidakova, Zh. I. Alferov, N. N. Ledentsov, A. Hoffmann, and D. Bimberg

Appl. Phys. Lett. 74, 3921 (1999); http://dx.doi.org/10.1063/1.124224 (3 pages) | Cited 13 times

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We report surface-mode lasing in a structure with 12-fold stacked InGaN insertions in a GaN matrix without using of Bragg mirrors. At high excitation densities, one of the modes of the Fabry–Perot cavity formed by the GaN sapphire and the GaN air interfaces, shows a strong superlinear increase in intensity with excitation density rise. The possibility to reach surface lasing in a very low finesse microcavity is due to the ultrahigh material gain of the InGaN insertions. The strong modulation of the absorption-gain spectrum with increase in the excitation density results in a pronounced energy shift of the cavity modes. We found that the threshold excitation density is weakly affected by temperature up to 110 K, while increases at higher temperatures. This behavior is attributed to thermal evaporation of carriers from InN-rich nanodomains and is typical for quantum dot lasers. © 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

A microscope for hard x rays based on parabolic compound refractive lenses

B. Lengeler, C. G. Schroer, M. Richwin, J. Tümmler, M. Drakopoulos, A. Snigirev, and I. Snigireva

Appl. Phys. Lett. 74, 3924 (1999); http://dx.doi.org/10.1063/1.124225 (3 pages) | Cited 75 times

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We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens. © 1999 American Institute of Physics.
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07.85.Tt X-ray microscopes
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Two-photon absorption in semiconductor saturable absorber mirrors

E. R. Thoen, E. M. Koontz, M. Joschko, P. Langlois, T. R. Schibli, F. X. Kärtner, E. P. Ippen, and L. A. Kolodziejski

Appl. Phys. Lett. 74, 3927 (1999); http://dx.doi.org/10.1063/1.124226 (3 pages) | Cited 24 times

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The nonlinear reflectivity of semiconductor saturable absorber mirrors has been investigated as a function of incident energy fluence. The presence of two-photon absorption in commonly used structures was confirmed via time-resolved differential reflectivity measurements. Theoretical calculations predict that two-photon absorption will expand the continuous-wave mode-locking stability regime against Q-switched mode-locking, yet may simultaneously induce multiple pulses in a laser cavity. © 1999 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.Bh Lenses, prisms and mirrors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
78.47.-p Spectroscopy of solid state dynamics

Indium tin oxide contacts to gallium nitride optoelectronic devices

T. Margalith, O. Buchinsky, D. A. Cohen, A. C. Abare, M. Hansen, S. P. DenBaars, and L. A. Coldren

Appl. Phys. Lett. 74, 3930 (1999); http://dx.doi.org/10.1063/1.124227 (3 pages) | Cited 85 times

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We have fabricated GaN-based light-emitting diodes using transparent indium tin oxide (ITO) p contacts. ITO-contacted devices required an additional 2 V to drive 10 mA, as compared to similar devices with metal contacts. However, ITO has lower optical absorption at 420 nm (α = 664 cm−1) than commonly used thin metal films (α = 3×105 cm−1). Uniform luminescence was observed in ITO-contacted devices, indicating effective hole injection and current spreading. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.40.Cg Contact resistance, contact potential

Optical photonic crystals fabricated from colloidal systems

G. Subramania, K. Constant, R. Biswas, M. M. Sigalas, and K.-M. Ho

Appl. Phys. Lett. 74, 3933 (1999); http://dx.doi.org/10.1063/1.124228 (3 pages) | Cited 78 times

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Photonic crystals of close-packed arrays of air spheres in a dielectric background of titania have been fabricated with a ceramic technique. Unlike previous methods, ordering of the spheres and the formation of the titania network are performed simultaneously. The photonic crystals exhibit a reflectance peak and a uniform color at the position of the first stop band. The wavelength of the reflectance peak scales very well with the sphere size. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
82.70.Dd Colloids

Bifunctional molecular glass for efficient photorefractive material

Kenji Ogino, Sang-Hun Park, and Hisaya Sato

Appl. Phys. Lett. 74, 3936 (1999); http://dx.doi.org/10.1063/1.124229 (3 pages) | Cited 17 times

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Two bifunctional succinates have been prepared as molecular photorefractive materials, which contain a hole-transporting triphenylamine moiety and an electro-optically active chromophore. The synthesized succinates formed stable amorphous glasses at room temperature. Succinate with 4-dicyanovinylaniline moiety as an electro-optic chromophore showed excellent photorefractive properties, i.e., 65% of diffraction efficiency, and 188 cm−1 of two-beam coupling gain at 60 V/μm, which are comparable to that observed in one of the most efficient photorefractive polymers. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ce Glasses, quartz
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Real-time monitoring of the Si carbonization process by a combined method of reflection high-energy electron diffraction and Auger electron spectroscopy

Ryoji Kosugi, Yuji Takakuwa, Ki-Seon Kim, Tadashi Abukawa, and Shozo Kono

Appl. Phys. Lett. 74, 3939 (1999); http://dx.doi.org/10.1063/1.124230 (3 pages) | Cited 9 times

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The carbonization process of a preferential-domain Si(001)2×1 surface with ethylene was investigated by a combined method of reflection high-energy electron diffraction and Auger electron spectroscopy. It is found that the carbonization process during the so-called incubation time is the Si1−xCx alloy formation before the nucleation of 3C–SiC grains. A reaction model for the Si1−xCx alloy formation and for the 3C–SiC grain growth is proposed for substrate temperatures of 600–750 °C. From the model, we postulate that the external supply of Si and C should be started just at the completion of the lateral 3C–SiC grain growth at temperatures of 600–650 °C in order to obtain thick 3C–SiC layers with a flat surface morphology. © 1999 American Institute of Physics.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Fv Electron impact: Auger emission
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

β-SiC nanorods synthesized by hot filament chemical vapor deposition

X. T. Zhou, N. Wang, H. L. Lai, H. Y. Peng, I. Bello, N. B. Wong, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 74, 3942 (1999); http://dx.doi.org/10.1063/1.124231 (3 pages) | Cited 76 times

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A one-step procedure has been developed to grow β-SiC nanorods from a solid carbon and silicon source on a Si substrate by hot filament chemical vapor deposition. This process is catalyzed by metallic particles which come from impurities in the solid source which is a plate made by pressing a mixture graphite and silicon powders at 150 °C. Hydrogen was introduced into the reaction chamber to react with the solid plate to produce hydrocarbon and hydrosilicon radicals which presumably reacted to form SiC nanorods. The nanorods consisted of a crystalline β-SiC core with an amorphous silicon oxide shell layer and grew along the [100] direction. The nanorods were 10–30 nm in diameter and less than 1 μm in length. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.-w Structure of nanoscale materials
81.05.Hd Other semiconductors

A method to produce reverse-mode polymer-dispersed liquid-crystal shutters

F. P. Nicoletta, G. De Filpo, J. Lanzo, and G. Chidichimo

Appl. Phys. Lett. 74, 3945 (1999); http://dx.doi.org/10.1063/1.124232 (3 pages) | Cited 19 times

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Reverse-mode operation shutters have been achieved by combining the techniques of the traditional means of making polymer-dispersed liquid crystals and nematic curvilinear aligned phases. Nematic microemulsions, obtained by a thermally induced phase separation, have been photopolymerized in an external force field. After the polymerization, films show 85% transmittance in the OFF state, while it decreases to less than 1% when an electric field of about 2 V μm−1 at 1 kHz is applied. The rise-time values, about 2 ms, are in the same range as those obtained with normal-mode polymer-dispersed liquid-crystal films. On the contrary, decay time shows longer values. © 1999 American Institute of Physics.  
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42.79.Ag Apertures, collimators
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
78.20.Jq Electro-optical effects
64.75.-g Phase equilibria
82.35.-x Polymers: properties; reactions; polymerization

Electron paramagnetic resonance of radiation defects in hydrogen-implanted silicon detected by spin-dependent microwave photoconductivity

R. Laiho, L. S. Vlasenko, M. P. Vlasenko, V. A. Kozlov, and V. V. Kozlovski

Appl. Phys. Lett. 74, 3948 (1999); http://dx.doi.org/10.1063/1.124233 (3 pages) | Cited 3 times

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Electron paramagnetic resonance (EPR) spectra of radiation defects induced by low-energy protons (100 keV) in a thin near-surface layer (L<1 μm) of silicon crystals are detected with spin-dependent microwave photoconductivity. It is found that EPR spectra of the excited triplet states of oxygen+vacancy complexes and spectra related to carbon-containing defects are formed at low proton irradiation doses of about 2×1012–1013 cm−2. When the irradiation dose is increased from 1013 to 5×1013 cm−2, a fast decrease of the intensity of the detected EPR spectra takes place. This effect is explained by passivation of the radiation defects by hydrogen. © 1999 American Institute of Physics.
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76.30.Mi Color centers and other defects
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
71.35.-y Excitons and related phenomena
72.80.Cw Elemental semiconductors
73.61.Cw Elemental semiconductors

Pulsed laser deposition of epitaxial GaNxAs1−x on GaAs

W. K. Hung, M. Y. Chern, J. C. Fan, T. Y. Lin, and Y. F. Chen

Appl. Phys. Lett. 74, 3951 (1999); http://dx.doi.org/10.1063/1.124234 (3 pages) | Cited 4 times

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Epitaxial layers of GaNxAs1−x were grown on (001) GaAs substrates by pulsed laser ablation of a GaAs target in an ammonia (NH3) atmosphere. High-resolution x-ray diffraction indicates the existence of a threshold NH3 pressure, above which the incorporated N content x increases linearly with increasing NH3 pressure. The band-gap dependence of GaNxAs1−x on x for x ⩽ 2.9% is examined by optical absorption and photoconductivity measurements at room temperature. We found that the band-gap energy reduces with higher N composition, and our results agree approximately with the prediction based on the dielectric model. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.05.Ea III-V semiconductors
68.55.Nq Composition and phase identification

Coherent array of tungsten ultrafine particles by laser irradiation

Yuji Kawakami, Eiichi Ozawa, and Shinya Sasaki

Appl. Phys. Lett. 74, 3954 (1999); http://dx.doi.org/10.1063/1.124248 (3 pages) | Cited 5 times

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We found a coherent array of tungsten ultrafine particles of about 700 nm around a laser-irradiated mark on a single-crystalline surface of tungsten. The tungsten specimens were irradiated by a short-pulse Nd:YAG laser under low pressure in an inert gas atmosphere. Two types of coherent arrays were observed that included the two-dimensional cubic and hexagonal systems. Such a coherent array of ultrafine particles may have potential applications for emission devices of plasma display and microelectronic devices. © 1999 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
81.05.Bx Metals, semimetals, and alloys

Transmission and photoluminescence images of three-dimensional memory in vitreous silica

Mitsuru Watanabe, Saulius Juodkazis, Hong-Bo Sun, Shigeki Matsuo, Hiroaki Misawa, Masafumi Miwa, and Reizo Kaneko

Appl. Phys. Lett. 74, 3957 (1999); http://dx.doi.org/10.1063/1.124235 (3 pages) | Cited 18 times

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We demonstrate separate readouts of three-dimensional memory by (i) transmission imaging using a conventional optical microscope and (ii) photoluminescence (PL) of the bits created by inducing optical damage within the vitreous silica. Recording was done by tightly focused (objective ×100, numerical aperture 1.3) single shot irradiation of 120 fs duration pulses at a 400 nm wavelength. For the readout, a broadband of PL at 470–600 nm was excited by 400 nm, 120 fs irradiation with pulse energy smaller by a factor of 106 compared with that for the recording. We found an erasing of the PL after 400 °C annealing, while the readability of the bits by the transmission was sustained. This shows the potential for two-bit information recording per single bit by means of separate readout procedures. © 1999 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
78.55.Hx Other solid inorganic materials

Optical properties of low-pressure metalorganic vapor phase epitaxy AlxGa1−xN thin-film waveguides by prism coupling technique

E. Dogheche, D. Remiens, and F. Omnes

Appl. Phys. Lett. 74, 3960 (1999); http://dx.doi.org/10.1063/1.124236 (3 pages) | Cited 8 times

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Epitaxial thin films of aluminum gallium nitride (AlxGa1−xN) were grown by low-pressure metalorganic vapor phase epitaxy on c-oriented sapphire substrates. The prism-coupling technique was carried out to determine the optical properties of Al0.17Ga0.93N thin films, i.e., the refractive index, the film thickness, and the optical loss. Optical transmission measurements were additionally used to determine the dispersion of the refractive index. A demonstration of optical waveguiding was successful in an AlGaN/AlN/sapphire planar structure, the optical propagation loss was determined to be around 1.8 dB cm−1 at 632.8 nm. An analysis of optical anisotropy using guided modes with the optical axis oriented normal to the film surface confirmed the uniaxial nature of the layer. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors

Suppression of temperature sensitivity of interband emission energy in 1.3-μm-region by an InGaAs overgrowth on self-assembled InGaAs/GaAs quantum dots

Kohki Mukai and Mitsuru Sugawara

Appl. Phys. Lett. 74, 3963 (1999); http://dx.doi.org/10.1063/1.124237 (3 pages) | Cited 38 times

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We found that the temperature sensitivity of interband emission energy was suppressed significantly in 1.3-μm-emitting self-assembled InGaAs/GaAs quantum dots by an InGaAs overgrowth on the dots. Transmission electron microscopy measurements indicated that lattice distortion was enhanced on dots in a 10-nm-thick InxGa1−xAs overgrowth layer. Photoluminescence spectra showed that the emission energy shift with increasing temperature was nearly negligible above 150 K when x ≥ 0.25. The shift between 4.2 and 200 K was less than half that of bulk GaAs when x = 0.3. The results reveal the potential of InGaAs-covered dots in realizing temperature-insensitive lasing wavelength of laser diodes by manipulating the three-dimensional strain distribution. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.55.Px Semiconductor lasers; laser diodes

Mechanism for photon emission from Au nano-hemispheres induced by scanning tunneling microscopy

Yish-Hann Liau and Norbert F. Scherer

Appl. Phys. Lett. 74, 3966 (1999); http://dx.doi.org/10.1063/1.124238 (3 pages) | Cited 3 times

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The photon emission yield observed in scanning tunneling microscopy (STM) measurements of Au hemispheroid-decorated thin films is used to elucidate the interaction of tunneling electrons with local surface plasmon modes. The photon emission probability is found to depend on the surface feature size. The agreement of a model calculation with the experimental results demonstrates that inelastic electron tunneling is the dominant mechanism of STM-induced plasmon excitation for 10–60 nm size metallic features. © 1999 American Institute of Physics.
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78.60.Fi Electroluminescence
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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Dose calibration for through-oxide doping distributions from time-dependent secondary-ion-mass-spectrometry depth profiles with only one sensitivity factor

K. Wittmaack, J. J. Lee, and S. B. Patel

Appl. Phys. Lett. 74, 3969 (1999); http://dx.doi.org/10.1063/1.124239 (3 pages) | Cited 5 times

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A simple method is described for calibrating the dose of impurity depth profiles in Si, SiO2, and SiO2 on Si by secondary ion mass spectrometry (SIMS). Use is made of the fact that, with normally incident O2+ beams, the ionization probabilities of impurity and matrix secondary ions as well as the partial Si sputtering yields are the same for Si and SiO2. This allows dose calibration against a reference sample to be achieved for any sequence of layers of the two materials and without depth calibration. SIMS profiles of 5 keV 11B equal-dose implants in Si, SiO2, and a thin layer of SiO2 on Si show that the concept is valid to ±1% or better. Differences in the reflection coefficient of 11B from the different targets could be identified clearly. © 1999 American Institute of Physics.
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61.72.S- Impurities in crystals
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors

An efficient way to improve compositional abruptness at the GaAs on GaInAs interface

E. Chirlias, J. Massies, J. L. Guyaux, H. Moisan, and J. Ch. Garcia

Appl. Phys. Lett. 74, 3972 (1999); http://dx.doi.org/10.1063/1.124240 (3 pages) | Cited 5 times

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Indium surface segregation during the growth of Ga1−xInxAs by chemical beam epitaxy is evidenced in real time by reflection high-energy electron diffraction. An efficient way to suppress the compositional broadening of GaAs on the GaInAs interface resulting from the In segregation effect is proposed. It consists in using the chemical reaction of AsCl3 molecules at the surface, which is shown to etch layer by layer the Ga1−xInxAs alloy. Monolayer etching precision is thus obtained and used to eliminate the In accumulation at the GaInAs surface and the related interface broadening. © 1999 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
68.35.Fx Diffusion; interface formation
81.65.Cf Surface cleaning, etching, patterning
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors

Effect of dangling-bond density on luminescence in tritiated amorphous silicon

Lakhbeer S. Sidhu, Tome Kosteski, Stefan Zukotynski, Nazir P. Kherani, and Walter T. Shmayda

Appl. Phys. Lett. 74, 3975 (1999); http://dx.doi.org/10.1063/1.124241 (3 pages) | Cited 7 times

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Self-luminescence in tritiated amorphous silicon is observed. The substitution of tritium for hydrogen in a hydrogenated semiconductor provides a powerful tool for the study of dangling bonds. The radioactive decay of tritium leads to an increase in the dangling-bond concentration in the material of several orders of magnitude over a period of a few weeks with little other modification in the structure of the material. We report here results of a study of photoluminescence as a function of time in tritiated amorphous silicon. An analysis of the data in terms of a simple theoretical model in which dangling bonds are treated as nonradiative recombination centers yields a capture radius of 32 Å for the D0 defect. © 1999 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
71.55.Jv Disordered structures; amorphous and glassy solids
78.47.-p Spectroscopy of solid state dynamics

Raman spectroscopy for characterizing compositional intermixing in GaAs/AlGaAs heterostructures

A. Saher Helmy, A. C. Bryce, C. N. Ironside, J. S. Aitchison, and J. H. Marsh

Appl. Phys. Lett. 74, 3978 (1999); http://dx.doi.org/10.1063/1.124242 (3 pages) | Cited 8 times

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Compositional intermixing induced by the process of impurity-free vacancy (dielectric cap annealing induced) disordering in GaAs/AlGaAs is studied using Raman spectroscopy. The degree of intermixing in multiple-quantum-well structures was detected through the energy shift of certain Raman modes of the lattices. In addition, localized intermixing, with band-gap shifts as low as 6 nm realized in 1:1 band-gap grating patterns with different periods (⩾4 μm), was also detected through the energy shift and the full width at half maximum of the structures’s Raman modes. © 1999 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Compositional fluctuations in GaInN/GaN double heterostructures investigated by selectively excited photoluminescence and Raman spectroscopy

N. Wieser, O. Ambacher, H.-P. Felsl, L. Görgens, and M. Stutzmann

Appl. Phys. Lett. 74, 3981 (1999); http://dx.doi.org/10.1063/1.124243 (3 pages) | Cited 18 times

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We report on compositional fluctuations in GaN/GaInN/GaN double heterostructures investigated by photoluminescence excitation and resonant Raman spectroscopy. The energy and line-shape of both luminescence and longitudinal optical (LO) phonon Raman peaks strongly depend on excitation energy due to selective excitation of regions with different In content. For a given excitation energy, luminescence from In-rich regions takes place and in addition, with increasing sample temperature, resonantly excited luminescence from regions of lower In content is superposed. Thus, the luminescence strongly broadens and on average shifts to higher energies with increasing temperature. The spectral variation of the photoluminescence and Raman cross sections is determined and correlated with the GaInN absorbance as measured by photothermal deflection spectroscopy. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.Nq Composition and phase identification
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Molecular beam epitaxial growth and optical properties of lattice-matched MgxZn1−xSeyTe1−y alloys on InP substrates

Koichi Naniwae, Hiroshi Iwata, and Kenichiro Yashiki

Appl. Phys. Lett. 74, 3984 (1999); http://dx.doi.org/10.1063/1.124244 (3 pages) | Cited 4 times

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Molecular beam epitaxial growth and the optical properties of lattice-matched MgxZn1−xSeyTe1−y alloys on InP were investigated. Two-dimensional growth and high crystalline quality were achieved by forming an InP buffer layer and a Zn0.48Cd0.52Se buffer layer before the MgxZn1−xSeyTe1−y layer growth. The band-gap energy (Eg) of the MgxZn1−xSeyTe1−y films, measured by optical-reflection measurements, increased with the Mg content and is expressed by the quadratic equation Eg = 0.90x2+0.83x+2.37. We found that the Stokes shifts of MgxZn1−xSeyTe1−y quaternary alloys, which seemed to originate from deep trap levels related to Te clusters, were larger than those of ZnSeTe ternary alloys. The refractive index of MgxZn1−xSeyTe1−y at a wavelength of 600 nm decreased as the Mg content rose, as expressed by the linear equation n600(x) = −1.09x+2.99. © 1999 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Negative photoconductivity in SiO2 films containing Si nanocrystals

Suk-Ho Choi and R. G. Elliman

Appl. Phys. Lett. 74, 3987 (1999); http://dx.doi.org/10.1063/1.124245 (3 pages) | Cited 12 times

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Negative photoconductivity is reported in metal–insulator–semiconductor structures containing Si nanocrystals produced by ion implantation and annealing. Under forward bias, the current is reduced when the sample is illuminated with ultraviolet light whilst under reverse bias it is increased. No such change is observed in structures that have not been ion implanted. This effect is explained by charging of nanocrystals in the oxide layer by photoionization of electrons. The positively charged nanocrystals screen the applied bias voltage leading to a reduction in current at a given voltage. This effect, if larger than the current increase caused by the photoexcitation of carriers in the accumulation layer, gives rise to the observed negative photoconductivity. © 1999 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ng Insulators
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Channeling implantations of Al+ into 6H silicon carbide

E. Morvan, P. Godignon, M. Vellvehi, A. Hallén, M. Linnarsson, and A. Yu. Kuznetsov

Appl. Phys. Lett. 74, 3990 (1999); http://dx.doi.org/10.1063/1.124246 (3 pages) | Cited 5 times

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A strong channeling effect of Al+ ions implanted into crystalline SiC has been observed by Monte Carlo simulations and experiments especially designed to demonstrate this phenomenon have been performed. Depth distributions of implanted Al were measured for on- and controlled off-axis Al implantations using secondary ion mass spectrometry (SIMS). Much deeper and wider profiles are obtained for the on-axis implantations as compared to off-axis implants. For higher doses, the experiment also reveals the growth of an intermediate peak slightly deeper than the random peak. The origin of the intermediate peak can be understood by combining SIMS results with Monte Carlo simulations, which motivates the development of advanced simulation tools for the ion implantation process in SiC. © 1999 American Institute of Physics.
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61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.S- Impurities in crystals

InxGa1−xN/GaN band offsets as inferred from the deep, yellow-red emission band in InxGa1−xN

Ch. Manz, M. Kunzer, H. Obloh, A. Ramakrishnan, and U. Kaufmann

Appl. Phys. Lett. 74, 3993 (1999); http://dx.doi.org/10.1063/1.124247 (3 pages) | Cited 20 times

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The deep, yellow photoluminescence band well known in GaN has been studied in InxGa1−xN (x ⩽ 0.14) grown pseudomorphically on GaN. The peak energy Ep of the band is found to shift gradually to the red with increasing x according to Ep = 2.20−2.02x (eV). As in the case of GaN, the deep band in InxGa1−xN is assigned to shallow donor-deep acceptor pair recombination. The data show that the deep acceptor level does not follow the valence band edge. It is therefore assumed to be pinned to a reference level common to GaN and InxGa1−xN. The band offsets between GaN and strained InxGa1−xN evaluated under this assumption, are found to be given by ΔEc(x) ≈ 2.02x (eV) and ΔEv(x) ≈ 1.26x (eV) for x⩽0.14. © 1999 American Institute of Physics.
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