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23 Feb 1998

Volume 72, Issue 8, pp. 873-995

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Electro-optic modulation of laser diode light by mode interference in a multilayer waveguide including a 2-docosylamino-5-nitropyridine Langmuir–Blodgett film

L. Palchetti, S. Sottini, D. Grando, E. Giorgetti, R. Ricceri, and G. Gabrielli

Appl. Phys. Lett. 72, 873 (1998); http://dx.doi.org/10.1063/1.120921 (3 pages) | Cited 2 times

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A hybrid four layer guide (FLG) including a glass guide and a 2-docosylamino-5-nitropyridine Langmuir–Blodgett film is described, and some tests are reported on an electro-optic modulator based on this FLG. The modulation of laser diode light was obtained by guided mode interference, without a Mach–Zehnder configuration of the device. From the modulated signal the r22 electro-optic coefficient was calculated as 11 pm/V. © 1998 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.79.Ry Gradient-index (GRIN) devices

Ultralow-threshold (50 A/cm2) strained single-quantum-well GaInAsSb/AlGaAsSb lasers emitting at 2.05 μm

G. W. Turner, H. K. Choi, and M. J. Manfra

Appl. Phys. Lett. 72, 876 (1998); http://dx.doi.org/10.1063/1.120922 (3 pages) | Cited 60 times

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Strained single-quantum-well, broadened-waveguide GaInAsSb/AlGaAsSb diode lasers have exhibited room-temperature threshold current densities as low as 50 A/cm2, one of the lowest values reported for diode lasers at room temperature. These lasers, grown by molecular beam epitaxy, have emission wavelengths of ∼ 2.05 μm, characteristic temperature of 65 K, internal quantum efficiency of 95%, and internal loss coefficient of 7 cm−1. Single-ended cw power of 1 W is obtained for a 100-μm aperture. © 1998 American Institute of Physics.  
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Self-diffraction from free surface relief gratings in a photorefractive Bi12TiO20 crystal

S. Stepanov, N. Korneev, A. Gerwens, and K. Buse

Appl. Phys. Lett. 72, 879 (1998); http://dx.doi.org/10.1063/1.120923 (3 pages) | Cited 14 times

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Experimental results on self-diffraction of periodically phase-modulated laser beams from a relief grating formed on a free surface of a cubic photorefractive Bi12TiO20 crystal due to the piezoelectric effect are reported. Periodic intensity modulations of the reflected beams up to 10−2 due to energy exchange at this unshifted phase grating are measured. The modulation depends linearly on the fringe spacing and on the amplitude of an externally applied electric dc field. The observed self-diffraction process is independent of the light polarization. © 1998 American Institute of Physics.
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78.20.-e Optical properties of bulk materials and thin films
42.79.Dj Gratings

Optical absorption and multiphonon relaxation of Nd3+ ions in ZnCl2-based glass

M. Shojiya, M. Takahashi, R. Kanno, Y. Kawamoto, and K. Kadono

Appl. Phys. Lett. 72, 882 (1998); http://dx.doi.org/10.1063/1.120924 (3 pages) | Cited 5 times

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Optical absorption and multiphonon relaxation have been investigated for Nd3+-doped ZnCl2-based glass. The intensity parameters for radiative transitions of Nd3+ were determined to be Ω2 = 4.97×10−20 cm2, Ω4 = 7.39×10−20 cm2 and Ω6 = 5.12×10−20 cm2. All of the Ωt parameters, especially Ω4, of Nd3+ in the ZnCl2-based glass were large compared with those reported for oxide and fluoride glasses. Multiphonon relaxation rates for three emission levels of Nd3+ were determined from lifetime measurements. The multiphonon relaxation rates in the ZnCl2-based glass were extremely low, because of the low-phonon-energy of the matrix. Values were found to obey the energy-gap law in the same manner as the values in Er3+-doped ZnCl2-based glasses. © 1998 American Institute of Physics.
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78.40.Pg Disordered solids
42.70.Ce Glasses, quartz
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
63.20.K- Phonon interactions
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Polymer-stabilized diffraction gratings from cholesteric liquid crystals

S. N. Lee, L. C. Chien, and S. Sprunt

Appl. Phys. Lett. 72, 885 (1998); http://dx.doi.org/10.1063/1.120925 (3 pages) | Cited 15 times

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We report the use of a low concentration polymer network to stabilize electric field-induced diffraction gratings in cholesteric liquid crystals. The stabilized gratings can be electrically switched between a zero-field “on” state, which exhibits approximately 75% diffraction efficiency, and a moderate field (typically 3 V/μm) “off” state. Grating spacings between 1.7 and 30 μm are obtained in a 10 μm thick cell by variation of the concentration of chiral dopant used to form the cholesteric liquid crystal. © 1998 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.79.Dj Gratings
78.20.Jq Electro-optical effects
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.

Effect of many weak side modes on relative intensity noise of distributed feedback semiconductor lasers

Eva Peral, William K. Marshall, Dan Provenzano, and Amnon Yariv

Appl. Phys. Lett. 72, 888 (1998); http://dx.doi.org/10.1063/1.120926 (3 pages) | Cited 4 times

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An increase of the relative intensity noise of nearly single-mode distributed feedback lasers with respect to that predicted by single-mode theory after propagation in dispersive fiber at frequencies up to 5 Ghz has been measured. A simplified multimode theory is presented which explains the increase in noise. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Mi Dynamical laser instabilities; noisy laser behavior
42.60.Fc Modulation, tuning, and mode locking

Electromagnetic characterization of vertical-cavity surface-emitting lasers based on a vectorial eigenmode calculation

D. Burak and R. Binder

Appl. Phys. Lett. 72, 891 (1998); http://dx.doi.org/10.1063/1.120927 (3 pages) | Cited 8 times

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A complete theoretical approach to the electromagnetic properties of vertical-cavity surface-emitting lasers (VCSELs) is presented. The solution of the 3D vector Maxwell equations is obtained by means of a generalized vectorial transform matrix. Results for the characterization of laser modes include modal frequencies, cavity losses, and eigenmode light-field vector patterns. As an example, modal properties of air-post index-guided VCSELs are analyzed for various cavity design parameters. Scattering losses due to modal mismatch at cavity interfaces are found to be small and, hence, would not overcompensate potential cavity design improvements based on increased relative index steps. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
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Quantum transport in metallic nanowires fabricated by electrochemical deposition/dissolution

C. Z. Li and N. J. Tao

Appl. Phys. Lett. 72, 894 (1998); http://dx.doi.org/10.1063/1.120928 (3 pages) | Cited 69 times

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A nonmechanical method for fabricating a metallic narrow constriction between two electrodes using electrochemical deposition is described. The width of the constriction can be adjusted by slowly dissolving metal atoms away or redepositing atoms onto the constriction which can be controlled flexibly by the electrodes’ potentials. Well-defined plateaus near the integer numbers of the conductance quantum have been observed in these constrictions at room temperature. Since no mechanical movements are involved, this method has the potential of fabricating nanoconstrictions with long term stability. © 1998 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
82.45.-h Electrochemistry and electrophoresis
81.15.Pq Electrodeposition, electroplating

Short-range disorder in lanthanum-doped lead titanate ceramics probed by Raman scattering

E. C. S. Tavares, P. S. Pizani, and J. A. Eiras

Appl. Phys. Lett. 72, 897 (1998); http://dx.doi.org/10.1063/1.120929 (3 pages) | Cited 28 times

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Raman scattering has been used to probe short-range structural information on lanthanum-doped lead titanate ceramics (LaxPb1−xTiO3) for x, ranging from 0.0 to 0.30. In highly doped samples (x>0.27), x-ray diffraction measurements indicate a cubic structure, although measurements of Raman scattering at temperatures above and below the tetragonal to cubic transition showed a residual short-range structural disorder in the cubic phase. Moreover, for these highly lanthanum-doped samples, a well-defined temperature-induced ferro–paraelectric phase transition disappears, which suggests a relationship between local disorder and relaxor behavior in this material. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.35.+c Brillouin and Rayleigh scattering; other light scattering
77.80.-e Ferroelectricity and antiferroelectricity

Rotating-compensator multichannel ellipsometry for characterization of the evolution of nonuniformities in diamond thin-film growth

Joungchel Lee, P. I. Rovira, Ilsin An, and R. W. Collins

Appl. Phys. Lett. 72, 900 (1998); http://dx.doi.org/10.1063/1.120930 (3 pages) | Cited 11 times

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A multichannel spectroscopic ellipsometer based on the rotating-compensator principle has been applied to obtain the evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a nanocrystalline diamond film during growth. Spectra in the ellipsometry angles (ψ, Δ) provide the time evolution of the microstructure and optical properties of the film in thin layers, whereas the spectra in the degree of polarization provide the time evolution of nonuniformities in the growth process attributed to light scattering by diamond nuclei in the initial stage of growth and to thickness gradients over the probed area in thicker layers. © 1998 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
78.66.Db Elemental semiconductors and insulators
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.07.-b Nanoscale materials and structures: fabrication and characterization

In situ determination of the surface roughness of diamond films using optical pyrometry

Z. L. Akkerman, Y. Song, Z. Yin, F. W. Smith, and Roy Gat

Appl. Phys. Lett. 72, 903 (1998); http://dx.doi.org/10.1063/1.120931 (3 pages) | Cited 6 times

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The initial growth of diamond films in a microwave plasma reactor has been studied using in situ two-color infrared pyrometry. Analysis of the observed oscillations of the apparent temperature has yielded the substrate temperature and also the instantaneous film growth rate and rms surface roughness σ. Two distinct regimes of growth have been clearly identified: an initial period of rapidly increasing σ before the diamond nuclei coalesce, followed by a slower increase of σ with thickness as the continuous film grows further. The differing initial roughnesses and emissivities of Si and Mo substrates have been shown to have important effects on the growth of diamond. © 1998 American Institute of Physics.  
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors

Secondary ion yield changes on rippled interfaces

Maxim A. Makeev and Albert-László Barabási

Appl. Phys. Lett. 72, 906 (1998); http://dx.doi.org/10.1063/1.120932 (3 pages) | Cited 8 times

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Sputter erosion often leads to the development of surface ripples. Here we investigate the effect of the ripples on the secondary ion yield, by calculating the yield as a function of the microscopic parameters characterizing the ion cascade (such as penetration depth, widths of the deposited energy distribution) and the ripples (ripple amplitude, wavelength). We find that ripples can strongly enhance the yield, with the magnitude of the effect depending on the interplay between the ion and ripple characteristics. Furthermore, we compare our predictions with existing experimental results.© 1998 American Institute of Physics.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Ct Interface structure and roughness

Microstructure of epitaxial SrRuO3 thin films on (001) SrTiO3

J. C. Jiang, X. Q. Pan, and C. L. Chen

Appl. Phys. Lett. 72, 909 (1998); http://dx.doi.org/10.1063/1.120870 (3 pages) | Cited 34 times

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Metallic oxide films of SrRuO3 deposited on (001) SrTiO3 by pulsed laser deposition have been investigated by transmission electron microscopy (TEM) techniques. These films have a single crystalline structure with an extremely smooth surface. A TEM study of cross-sectional samples shows that the film grew epitaxially on the (001) surface of the SrTiO3 substrate. The films grew along the [110] directions with an in-plane orientation relationship of either SrRuO3[110]//SrTiO3 [100] and SrRuO3[001]//SrTiO3[010], or SrRuO3[110]//SrTiO3[010] and SrRuO3[001]//SrTiO3 [100]. Domains with a rotation of 90° around SrRuO3[110] were observed in the dark-field image of plan-view samples. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology

Defect induced lowering of activation energies at step bands in Co/Cu(100)

S. T. Coyle, M. R. Scheinfein, and James L. Blue

Appl. Phys. Lett. 72, 912 (1998); http://dx.doi.org/10.1063/1.120871 (3 pages) | Cited 4 times

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Complex topological features such as rectangular voids and step inclusions that were seen in secondary electron micrographs of Co films grown on Cu(100) at room temperature were reproduced in Monte Carlo simulations in the presence of step bands. Lowered activation energies at defects such as steps, kinks, and vacancies enhance step edge restructuring during growth and upon annealing. This results in features such as faceted step edges, rectangular pits, incorporation of Co into terraces, surface alloying, and surface segregation. Simulated growth structures are directly compared with those observed in an ultrahigh vacuum scanning transmission electron microscope. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Fx Diffusion; interface formation
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.J- Point defects and defect clusters

Potentiometry and repair of electrically stressed nanowires using atomic force microscopy

M. C. Hersam, A. C. F. Hoole, S. J. O’Shea, and M. E. Welland

Appl. Phys. Lett. 72, 915 (1998); http://dx.doi.org/10.1063/1.120872 (3 pages) | Cited 36 times

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Using an atomic force microscope equipped with a conducting diamond tip, the surface potential on a current carrying gold nanowire was measured with microvolt potential sensitivity and nanometer spatial resolution. Potentiometry images illustrate the stages of failure of nanowires subjected to current stressing. During this failure process, a discontinuity in the potential gradient and an enhanced resistance region were observed at the failure site until a complete fracture was formed. By increasing the repulsive force and accurately positioning the tip, gold could be manipulated into the nanoscale fracture so that the electrical conductivity of the nanowire was regained. © 1998 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.25.+i Surface conductivity and carrier phenomena

Mechanical relaxation and “intramolecular plasticity” in carbon nanotubes

B. I. Yakobson

Appl. Phys. Lett. 72, 918 (1998); http://dx.doi.org/10.1063/1.120873 (3 pages) | Cited 142 times

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The question of how carbon nanotubes (CNT)—believed to be the strongest filaments—relax under tension has been addressed. A dislocation theory applied to a two-dimensional nanocrystal such as the CNT describes the main routes of mechanical relaxation in this molecular structure: a brittle cleavage or, at high temperatures, a plastic flow. Both start with diatomic rotation, which “unlocks” the pristine wall of CNT by creating a dislocation dipole with the pentagon–heptagon cores. Under high stress, the dislocations depart from each other along helical paths, leaving behind a nanotube of smaller diameter, well-defined new symmetry, and changed electrical properties. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.Bb Theories and models of crystal defects
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Magnesium induced changes in the selective growth of GaN by metalorganic vapor phase epitaxy

B. Beaumont, S. Haffouz, and P. Gibart

Appl. Phys. Lett. 72, 921 (1998); http://dx.doi.org/10.1063/1.120874 (3 pages) | Cited 54 times

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Atmospheric pressure metalorganic vapor phase epitaxy is used to perform selective regrowth of GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. The basic pattern is constituted by a 15 μm period hexagonal array of hexagonal openings in the mask, these openings being circumscribed into 10 μm diam circles. We investigate the effect of Mg incorporation on the growth anisotropy of the localized GaN islands by varying the ratio [Mg]/[Ga] of bis-methylcyclopentadienyl-magnesium and trimethylgallium partial pressures. Both undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R (1 101) facets, are achieved with a good selectivity. It is found that the GaN growth rates VR and VC, measured in the R〈1math01〉 and C 〈0001〉 directions respectively, are drastically affected by the Mg incorporation. By adjusting the Mg partial pressure in the growth chamber, the VR/VC ratio can be increased so that the delimiting top C facet does not vanish as usually observed in undoped GaN localized growth, but by contrast expands. © 1998 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors

Two-peak electroluminescence of porous silicon in persulphate solution

R. Q. Wang, J. J. Li, S. M. Cai, Z. F. Liu, and S. L. Zhang

Appl. Phys. Lett. 72, 924 (1998); http://dx.doi.org/10.1063/1.120619 (3 pages)

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A large blue shift of electroluminescence (EL) was achieved from oxidized n-type porous silicon (PS) in a persulphate solution under cathodic polarization. The two-peak phenomenon observed in the EL spectrum suggests that there are two types of luminescent centers located in the nanoscale silicon particles and at the surface of the oxidized PS layer, respectively. It is found that only the low-energy peak having luminescent centers in nanoscale silicon particles can be tuned by voltage, supporting the quantum confinement model. © 1998 American Institute of Physics.
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78.60.Fi Electroluminescence

Near-field scanning optical spectroscopy of an InGaN quantum well

P. A. Crowell, D. K. Young, S. Keller, E. L. Hu, and D. D. Awschalom

Appl. Phys. Lett. 72, 927 (1998); http://dx.doi.org/10.1063/1.120875 (3 pages) | Cited 26 times

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Near-field scanning optical microscopy is used to image photoluminescence (PL) in an InGaN/GaN quantum well (QW) with spatial resolution of approximately 100 nm for temperatures between 50 and 295 K. Strong (∼50%) fluctuations in the quantum well photoluminescence as well as a tenfold enhancement of deep level-related emission at lower energies occur at large (∼500 nm diam) pits in the heterostructure. Regions of smaller (∼15%) fluctuations in the QW PL are not correlated with the presence of pits. The spectrum of the QW PL shows no significant variations on the length scales probed in this experiment. We thus find no spectroscopic signature of the recombination of strongly localized carriers at temperatures above 50 K. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
07.79.Fc Near-field scanning optical microscopes
78.55.Cr III-V semiconductors
07.79.Lh Atomic force microscopes
71.55.Eq III-V semiconductors
07.60.Rd Visible and ultraviolet spectrometers

Growth and characterization of thin Si80C20 films based upon Si4C building blocks

J. Kouvetakis, D. Chandrasekhar, and David J. Smith

Appl. Phys. Lett. 72, 930 (1998); http://dx.doi.org/10.1063/1.120876 (3 pages) | Cited 8 times

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The growth of thin Si80C20 diamond-structured material on (100)Si has been achieved using the novel C–H free, carbon source tetrasilyl methane, C(SiH3)4. The precursor decomposes at temperatures in the range 600–700 °C to give thin amorphous layers with a composition of Si0.80C0.20, which corresponds to the same relative concentrations of Si and C as in the precursor. The amorphous material is crystallized via solid-phase epitaxy by annealing at 825 °C to yield a potentially ordered structure in which Si4C tetrahedra are linked together in a three-dimensional diamond-cubic framework. Measured lattice parameters are larger than expected from Vegards’ Law, a discrepancy which is attributed to steric repulsions causing bond elongation. © 1998 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases
81.40.Gh Other heat and thermomechanical treatments

In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions

B. Ren, F. M. Liu, J. Xie, B. W. Mao, Y. B. Zu, and Z. Q. Tian

Appl. Phys. Lett. 72, 933 (1998); http://dx.doi.org/10.1063/1.120877 (3 pages) | Cited 11 times

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In situ Raman spectra of SiHx, Si–F, and Si–Si vibrations from Si surfaces in HF aqueous solutions are obtained using a highly sensitive confocal microprobe Raman system. Electrochemical roughening pretreatment and laser-assisted roughening procedure enable good quality surface Raman spectra to be obtained. The surface Raman and photoluminescence spectra from the Si surface in the etching environment and the correlation of the two types of spectra are discussed. The Raman spectroscopy is shown to have high potential in serving as an important tool for in situ investigating of Si surface bonding during the etching process. © 1998 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
68.35.Ja Surface and interface dynamics and vibrations
78.55.Ap Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning

Influence of rapid thermal annealing on the optical properties of gallium nitride grown by gas-source molecular-beam epitaxy

X. B. Li, D. Z. Sun, J. P. Zhang, M. Y. Kong, and S. F. Yoon

Appl. Phys. Lett. 72, 936 (1998); http://dx.doi.org/10.1063/1.120878 (3 pages) | Cited 7 times

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Raman scattering, photoluminescence (PL), and nuclear reaction analysis (NRA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by gas-source molecular-beam epitaxy. The Raman spectra showed the presence of the E2 (high) mode of GaN and shift of this mode from 572 to 568 cm−1 caused by annealing. The results showed that RTA has a significant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL peak exhibited a blueshift in its energy position and a decrease in the full width at half maximum after annealing, indicating an improvement in the optical quality of the film. Furthermore, a green luminescence appeared after annealing and increased in intensity with increasing annealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exists in as-grown GaN, which can neutralize the deep level, and the H-bonded complex dissociates during RTA. This leads to the appearance of a luminescent peak in the PL spectrum. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
65.40.De Thermal expansion; thermomechanical effects
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
82.80.-d Chemical analysis and related physical methods of analysis
68.60.Bs Mechanical and acoustical properties
68.60.Dv Thermal stability; thermal effects

Deep ultraviolet enhanced wet chemical etching of gallium nitride

L.-H. Peng, C.-W. Chuang, J.-K. Ho, C.-N. Huang, and C.-Y. Chen

Appl. Phys. Lett. 72, 939 (1998); http://dx.doi.org/10.1063/1.120879 (3 pages) | Cited 52 times

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We report a study of the ultraviolet (UV) irradiation effects on the wet chemical etching of unintentionally doped n-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated with a 253.7 nm mercury line source, etching of GaN is found to take place in aqueous phosphorus acid (H3PO4) and potassium hydroxide (KOH) solutions of pH values ranging from −1 to 2 and 11 to 15, respectively. Formation of gallium oxide is observed on GaN when illuminated in dilute H3PO4 and KOH solutions. These results are attributed to a two-step reaction process upon which the UV irradiation is shown to enhance the oxidative dissolution of GaN. © 1998 American Institute of Physics.  
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Gain studies of (Cd, Zn)Se quantum islands in a ZnSe matrix

M. Strassburg, V. Kutzer, U. W. Pohl, A. Hoffmann, I. Broser, N. N. Ledentsov, D. Bimberg, A. Rosenauer, U. Fischer, D. Gerthsen, I. L. Krestnikov, M. V. Maximov, P. S. Kop’ev, and Zh.I. Alferov

Appl. Phys. Lett. 72, 942 (1998); http://dx.doi.org/10.1063/1.120880 (3 pages) | Cited 88 times

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By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnSe matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energy side of the absorption peak. Efficient waveguiding can thus be achieved without increasing the average refractive index of the active layer with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement for excitons. Zero-phonon gain is observed in the spectral range of excitonic and biexcitonic waveguiding. At high excitation densities excitonic gain is suppressed due to the population of the quantum dots with biexcitons. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.45.+h Stimulated emission
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.)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.-e Phonons in crystal lattices
42.55.Px Semiconductor lasers; laser diodes

Optical characterization of GaN/SiC n-p heterojunctions and p-SiC

John T. Torvik, Chang-hua Qiu, Moeljanto Leksono, and Jacques I. Pankove

Appl. Phys. Lett. 72, 945 (1998); http://dx.doi.org/10.1063/1.120881 (3 pages) | Cited 18 times

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Optical characterization of GaN/SiC heterojunctions and p-SiC has been performed to explain the current–voltage (I–V) characteristics in GaN/SiC n-p heterojunction diodes. The I–V characteristics exhibit tunneling-assisted current with low forward “turn-on” voltages around 1.15 V as opposed to the expected drift/diffusion current with a turn on around 2.5 V. Electroluminescence (EL) measurements on these diodes revealed an infrared peak at 1.25 eV and a red peak at 1.75 eV. Photoluminescence (PL) measurements on p-SiC yielded peaks at 1.25 and 1.80 eV. Since the band gap of 6H–SiC is 3.03 eV, we attribute the EL and PL peaks to radiative transitions from the conduction band edge to a defect level and subsequently down to the valence band edge of p-SiC. This defect level is located 1.25 eV above the valence band edge. © 1998 American Institute of Physics.
Show PACS
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
78.66.Li Other semiconductors
71.55.Ht Other nonmetals
73.40.Gk Tunneling
78.55.Hx Other solid inorganic materials
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