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27 Apr 1998

Volume 72, Issue 17, pp. 2069-2187

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Polarization-dependent efficiency of photoconducting THz transmitters and receivers

P. G. Huggard, C. J. Shaw, J. A. Cluff, and S. R. Andrews

Appl. Phys. Lett. 72, 2069 (1998); http://dx.doi.org/10.1063/1.121278 (3 pages) | Cited 12 times

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The emission and detection efficiencies of photoconducting THz transmitters and receivers are found to be sensitive to the polarization of the optical gating pulse. Signal amplitudes from GaAs coplanar stripline transmitters and silicon-on-sapphire dipole receivers vary by factors of up to 4 and 3, respectively, with rotation of the exciting pulse polarization. In both cases, maximum signal is obtained when the polarization of the normally incident light is perpendicular to the edge of the metal electrodes. This polarization sensitivity, which appears to arise from differences in the spatial distribution of photoexcited carriers in the semiconductor, needs to be considered when optimizing the signal-to-noise ratio in coherent THz spectroscopy. © 1998 American Institute of Physics.
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85.60.-q Optoelectronic devices
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Defect-enhanced second-harmonic generation in (SimGen)p superlattices

Chun Zhang, Xudong Xiao, N. Wang, K. K. Fung, M. M. T. Loy, Zhenghao Chen, and Junming Zhou

Appl. Phys. Lett. 72, 2072 (1998); http://dx.doi.org/10.1063/1.121279 (3 pages) | Cited 5 times

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Second-harmonic generation (SHG) has been applied to study the influence of defects in short-period (SimGen)p strained-layer superlattices. With a misfit stacking fault defect density of ∼ 1010 cm−2 shown by transmission electron microscopy, it is found that the SH intensity increases by about one order of magnitude from that of the defect-free samples. We propose that the inhomogeneous strain field around the fault planes in the superlattice layers is responsible for this abrupt increase of SHG. The expected symmetry and the magnitude of the nonlinear susceptibility from these stacking fault defects are shown to be in agreement with the experimental observations. © 1998 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.72.Nn Stacking faults and other planar or extended defects
68.35.Ct Interface structure and roughness
42.65.An Optical susceptibility, hyperpolarizability
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Laser field enhancement at the scanning tunneling microscope junction measured by optical rectification

A. V. Bragas, S. M. Landi, and O. E. Martínez

Appl. Phys. Lett. 72, 2075 (1998); http://dx.doi.org/10.1063/1.121280 (3 pages) | Cited 26 times

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In this letter we report the measurement of the field enhancement at the tip of a scanning tunneling microscope, by means of the detection of the optical rectification current. A field enhancement factor between 1000 and 2000 is obtained for highly oriented pyrolytic graphite and between 300 and 600 for gold. Field enhancement factors found are strongly dependent on the particular tip used. The magnitude of the emitted light at the field enhanced region, calculated from the measured optical voltage, could be easily detected by a simple photodiode. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
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

Laser etched gratings on polymer layers for alignment of liquid crystals

C. J. Newsome, M. O’Neill, R. J. Farley, and G. P. Bryan-Brown

Appl. Phys. Lett. 72, 2078 (1998); http://dx.doi.org/10.1063/1.121281 (3 pages) | Cited 43 times

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Liquid crystal alignment layers are prepared using a noncontact method based on laser ablation. Nonpolarized light from a KrF excimer laser at 248 nm is exposed through a phase mask to etch gratings of period 1.1 μm onto polyimide alignment layers. Twisted nematic cells were prepared using one rubbed and one grating aligned surface, and azimuthal anchoring energies were found from measurements of the twist angles as a function of grating depth. The measured anchoring energies agree with those predicted from the minimization of elastic strain energy when the liquid crystal directors at the surface are aligned parallel to the groove of the grating. This suggests that topographical rather than epitaxial alignment is achieved. © 1998 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
81.65.Cf Surface cleaning, etching, patterning
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena

Local optical spectroscopy of self-assembled quantum dots using a near-field optical fiber probe to induce a localized strain field

H. D. Robinson, M. G. Müller, B. B. Goldberg, and J. L. Merz

Appl. Phys. Lett. 72, 2081 (1998); http://dx.doi.org/10.1063/1.121282 (3 pages) | Cited 17 times

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We introduce and demonstrate a novel operating mode in near-field optical microscopy. The tip is used to simultaneously optically probe the sample and induce a highly localized strain in the area under study by pushing the tip into the sample. From knowledge of total tip-sample compression and tip geometry, we estimate the magnitude of stress, and show that localized uniaxial-like stresses in excess of 10 kbar can be achieved. We apply this method to a sample of InAlAs self-assembled quantum dots. A blueshift of quantum dot emission lines consistent with estimates of the strain is observed, as well as a quenching of the photoluminescence with strain. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.Gy Mechanical properties; surface strains
78.55.Cr III-V semiconductors

Analog measurements of long wavelength vertical-cavity lasers

Jon R. Wesselmann, Near M. Margalit, and John E. Bowers

Appl. Phys. Lett. 72, 2084 (1998); http://dx.doi.org/10.1063/1.121283 (3 pages) | Cited 9 times

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We report the measurements of nonlinearity effects on analog transmission of long wavelength vertical-cavity surface-emitting lasers. The experiments involved measuring single-mode fiber-optic transmissions of microwave signals (100–1000 MHz) at 1.54 μm to characterize the dynamic range, intermodulation distortion and frequency response. Spur free dynamic ranges up to 69 dB were demonstrated. © 1998 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.65.-k Nonlinear optics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.81.Dp Propagation, scattering, and losses; solitons

The four-level stimulated emission in sexithiophene single crystals

Francis Garnier, Gilles Horowitz, Pierre Valat, Fayçal Kouki, and Véronique Wintgens

Appl. Phys. Lett. 72, 2087 (1998); http://dx.doi.org/10.1063/1.121284 (3 pages) | Cited 25 times

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Single crystal of conjugated sexithiophene oligomer shows stimulated emission when excited with a low-energy photonic pulse. This phenomenon is interpreted in terms of the excitonic energy diagram of the crystal, which presents a four-level pathway for the photoexcitation and emission, similar to the one observed in classical inorganic-based laser materials. © 1998 American Institute of Physics.
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78.45.+h Stimulated emission
42.55.Px Semiconductor lasers; laser diodes
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Suppression of electron and hole leakage in 1.3 μm AlGaInAs/InP quantum well lasers using multiquantum barrier

Jen-Wei Pan, Ken-Gi Chau, Jen-Inn Chyi, Yuan-Kuang Tu, and Jy-Wang Liaw

Appl. Phys. Lett. 72, 2090 (1998); http://dx.doi.org/10.1063/1.121285 (3 pages) | Cited 9 times

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The slope efficiency and threshold current density of 1.3 μm AlGaInAs/InP lasers with AlInAs–AlGaInAs multiquantum barrier (MQB) are experimentally studied and compared with the conventional step-index separate confinement heterostructure (SCH) laser. With the MQBs at the guiding layers, the characteristic temperature can be improved as much as 10 K as compared with the conventional SCH laser. This is attributed to the suppression of electron and hole leakage currents. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High slope efficiency, “cascaded” midinfrared lasers with type I InAsSb quantum wells

S. R. Kurtz, A. A. Allerman, R. M. Biefeld, and K. C. Baucom

Appl. Phys. Lett. 72, 2093 (1998); http://dx.doi.org/10.1063/1.121286 (3 pages) | Cited 7 times

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Lasers and light-emitting diodes with multistage, type I InAsSb/InAsP quantum well active regions are reported. These ten stage, cascaded devices were grown by metalorganic chemical vapor deposition. The broadband light-emitting diodes produced high average powers, >2 mW ( ∼ 80 K, 3.7 μm) and >0.1 mW ( ∼ 300 K, 4.3 μm). A 3.8–3.9 μm laser structure operated up to T = 180 K. At 80 K, peak power >100 mW and a slope efficiency of 48% (4.8% per stage) were observed in our gain guided lasers. The slope efficiency was strongly dependent on cavity length, and analysis of efficiency data suggests an internal differential quantum efficiency >1 and a loss coefficient ≥ 100 cm−1. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Gradient force: The mechanism for surface relief grating formation in azobenzene functionalized polymers

Jayant Kumar, Lian Li, Xin Li Jiang, Dong-Yu Kim, Taek Seung Lee, and Sukant Tripathy

Appl. Phys. Lett. 72, 2096 (1998); http://dx.doi.org/10.1063/1.121287 (3 pages) | Cited 155 times

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A model for the formation of holographic surface relief gratings in azobenzene functionalized polymers is presented. Forces leading to migration of polymer chains upon exposure to light in the absorption band of the azo chromophore are attributed to dipoles interacting with the gradient of the electric field present in the polymer material. Efficient trans–cis cycling in the azobenzenes allows cooperative movement of the chromophores under the influence of gradient forces. © 1998 American Institute of Physics.
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42.70.Jk Polymers and organics
42.40.Eq Holographic optical elements; holographic gratings
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics
82.50.-m Photochemistry
82.30.Qt Isomerization and rearrangement
82.35.-x Polymers: properties; reactions; polymerization
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
42.70.Gi Light-sensitive materials
42.70.Ln Holographic recording materials; optical storage media
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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Spatially resolved photoluminescence in GaAs surface acoustic wave structures

P. V. Santos, M. Ramsteiner, and F. Jungnickel

Appl. Phys. Lett. 72, 2099 (1998); http://dx.doi.org/10.1063/1.121288 (3 pages) | Cited 25 times

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The interaction between a surface acoustic wave (SAW) and the excitonic photoluminescence (PL) in GaAs SAW structures is investigated. The dependence of the PL on the SAW amplitude and illumination intensity is explained by a simple model based on the field-induced ionization of the excitons and on the screening of the SAW electric field by photogenerated carriers. Microscopic PL constitutes a powerful technique for spatially resolving electric-field distributions in SAW structures. © 1998 American Institute of Physics.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
68.35.Gy Mechanical properties; surface strains
78.55.Cr III-V semiconductors
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Equilibrium phase diagrams for dislocation free self-assembled quantum dots

István Daruka and Albert-László Barabási

Appl. Phys. Lett. 72, 2102 (1998); http://dx.doi.org/10.1063/1.121289 (3 pages) | Cited 36 times

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The equilibrium theory of self-assembled quantum dot (SAQD) formation can account for many of the experimentally observed growth modes. Here, we show that despite the large number of material constants entering the free energy of strained islands, there are only four topologically different phase diagrams describing the SAQD formation process. We derive each of these phase diagrams and discuss the physical properties of the predicted growth modes.© 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Md Surface thermodynamics, surface energies
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
68.35.Rh Phase transitions and critical phenomena

X-ray absorption spectroscopy and atomic force microscopy study of bias-enhanced nucleation of diamond films

M. M. García, I. Jiménez, L. Vázquez, C. Gómez-Aleixandre, J. M. Albella, O. Sánchez, L. J. Terminello, and F. J. Himpsel

Appl. Phys. Lett. 72, 2105 (1998); http://dx.doi.org/10.1063/1.121290 (3 pages) | Cited 27 times

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The bias-enhanced nucleation of diamond on Si(100) has been studied by x-ray absorption near-edge spectroscopy (XANES) and atomic force microscopy, two techniques well suited to characterize nanometric crystallites. Diamond nuclei of ∼ 15 nm are formed after 5 min of bias-enhanced treatment. The number of nuclei and its size increases with the time of application of the bias voltage. A nanocrystalline diamond film is attained after 20 min of bias-enhanced nucleation. At the initial nucleation stages, the Si substrate appears covered with diamond crystallites and graphite, without SiC being detected by XANES. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.70.Dm X-ray absorption spectra
61.46.-w Structure of nanoscale materials

Boron-doped carbon fullerenes and nanotubules formed through electron irradiation-induced solid-state phase transformation

D. Golberg, Y. Bando, K. Kurashima, and T. Sasaki

Appl. Phys. Lett. 72, 2108 (1998); http://dx.doi.org/10.1063/1.121291 (3 pages) | Cited 25 times

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Here we report on the in situ creation of single/multi-shelled fullerenes and multi-walled nanotubules by electron irradiation of chemical vapor deposit graphitic BxC1−x (x ⩽ 0.2) in a high-resolution 300 kV electron microscope. Nanostructure formation occurred through irradiation-induced solid-state phase transformation, in contrast to conventional fullerene/nanotube synthesis from the gas phase. The fullerene/nanotubule chemical composition and bonding character were analyzed by electron energy loss spectroscopy applying a ∅0.5 nm electron probe. The B/C ratio of the observed curled, closed nanostructures has never exceeded ∼ 0.1. Unlike pure carbon “onions,” most of the B-doped fullerenes exhibited a polyhedral faceted circumference suggestive of B-induced buckling. © 1998 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
61.80.Fe Electron and positron radiation effects
64.70.K- Solid-solid transitions
79.20.Kz Other electron-impact emission phenomena

Effect of film density on boron diffusion in SiO2

Mitra Navi and Scott T. Dunham

Appl. Phys. Lett. 72, 2111 (1998); http://dx.doi.org/10.1063/1.121292 (3 pages) | Cited 9 times

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Oxides grown at low temperatures exhibit higher density than those grown or annealed at high temperatures. This work investigates the role of oxide density on boron diffusion through thin gate dielectrics. Capacitor structures were fabricated by depositing polycrystalline silicon on top of 54–60 Å oxide films grown at 800 °C in dry O2. A subset of these high density oxides were then annealed at 1100 °C to relax the grown-in stress. Following ion implantation of boron into the polysilicon, the capacitor structures were annealed in an inert ambient at 950 °C to allow boron penetration. Capacitance–voltage measurements revealed that boron penetration was greatly enhanced for the films that saw the high temperature relaxation anneal, leading to the conclusion that boron diffusion in SiO2 is retarded in the presence of excess density. © 1998 American Institute of Physics.
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66.30.J- Diffusion of impurities
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
61.72.Cc Kinetics of defect formation and annealing
68.60.Wm Other nonelectronic physical properties
85.30.Tv Field effect devices
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Determination of wurtzite GaN lattice polarity based on surface reconstruction

A. R. Smith, R. M. Feenstra, D. W. Greve, M.-S. Shin, M. Skowronski, J. Neugebauer, and J. E. Northrup

Appl. Phys. Lett. 72, 2114 (1998); http://dx.doi.org/10.1063/1.121293 (3 pages) | Cited 159 times

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We identify two categories of reconstructions occurring on wurtzite GaN surfaces, the first associated with the N face, (0001), and the second associated with the Ga face, (0001). Not only do these two categories of reconstructions have completely different symmetries, but they also have different temperature dependence. It is thus demonstrated that surface reconstructions can be used to identify lattice polarity. Confirmation of the polarity assignment is provided by polarity-selective wet chemical etching of these surfaces. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
81.65.Cf Surface cleaning, etching, patterning

Strategies for the synthesis of highly concentrated Si1−yCy diamond-structured systems

D. Chandrasekhar, J. McMurran, David J. Smith, J. Kouvetakis, J. D. Lorentzen, and J. Menéndez

Appl. Phys. Lett. 72, 2117 (1998); http://dx.doi.org/10.1063/1.121294 (3 pages) | Cited 9 times

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Precursor chemistry and ultrahigh-vacuum chemical vapor deposition have been used to deposit Si1−yCy thin films on (001) Si substrates. Films with carbon compositions ranging up to 20 at. % were deposited at substrate temperatures of 600–740 °C using gas mixtures of SiH4 with C(SiH3)4 or C(SiH2Cl)4, which are (C–H)-free precursors incorporating Si4C tetrahedra. The composition of the resulting materials was obtained by Rutherford backscattering spectrometry, including carbon resonance analysis. Cross-sectional transmission electron microscopy and infrared spectroscopy were used to provide microstructural and bonding information. Raman spectroscopy suggested that the substitutional C concentration obtained using this protocol was higher than that obtained by other methods. The addition of small amounts of GeH4 to the gas mixture had a remarkable effect on growth rates and film crystallinity. © 1998 American Institute of Physics.
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81.05.Hd Other semiconductors
68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Le Other inorganic semiconductors
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
71.20.Nr Semiconductor compounds

Transverse magnetic field studies in ZnSe/BeTe resonant tunneling structures

U. Lunz, M. Keim, A. Waag, W. Faschinger, and G. Landwehr

Appl. Phys. Lett. 72, 2120 (1998); http://dx.doi.org/10.1063/1.121295 (3 pages) | Cited 1 time

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We report on resonant electron tunneling in ZnSe/BeTe double-barrier, single-quantum-well heterostructures under high magnetic fields. Current–voltage characteristics have been investigated in the presence of a magnetic field B perpendicular to the tunneling current (B⊥I). The effect of the field on the main resonance position as well as two additional features due to optical phonon assisted tunneling into the quantum well has been studied and analyzed. The peak bias voltage exhibits a quadratic shift with increasing magnetic field due to a Lorentz force acting on the tunneling electrons. The phonon peaks do not shift, because the transverse momentum is no longer conserved during this process. © 1998 American Institute of Physics.
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73.61.Ga II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.23.-b Electronic transport in mesoscopic systems
72.20.My Galvanomagnetic and other magnetotransport effects

Ordered InAs quantum dots in InAlAs matrix on (001) InP substrates grown by molecular beam epitaxy

Hanxuan Li, Ju Wu, Bo Xu, Jiben Liang, and Zhanguo Wang

Appl. Phys. Lett. 72, 2123 (1998); http://dx.doi.org/10.1063/1.121296 (3 pages) | Cited 17 times

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InAs self-organized quantum dots in InAlAs matrix lattice-matched to exactly oriented (001) InP substrates were grown by solid source molecular beam epitaxy (MBE) using the Stranski-Krastanow mode. Preliminary characterizations have been performed using photoluminescence and transmission electron microscopy. The geometrical arrangement of the quantum dots is found to be strongly dependent on the amount of coverage. At low deposition thickness. InAs QDs are arranged in chains along [110] directions. Luminescence from the quantum dots and the wetting layer consisting of quantum wells with well widths of 1, 2, and 3 monolayers is observed. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Formation of PIn defect in annealed liquid-encapsulated Czochralski InP

Y. W. Zhao, X. L. Xu, M. Gong, S. Fung, C. D. Beling, X. D. Chen, N. F. Sun, T. N. Sun, S. L. Liu, G. Y. Yang, X. B. Guo, Y. Z. Sun, L. Wang, Q. Y. Zheng, Z. H. Zhou, et al.

Appl. Phys. Lett. 72, 2126 (1998); http://dx.doi.org/10.1063/1.121297 (3 pages) | Cited 21 times

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Fourier transform infrared spectroscopy measurements have been carried out on liquid-encapsulated Czochralski-grown undoped InP wafers, which reproducibly become semi-insulating upon annealing in an ambient of phosphorus at 800–900 °C. The measurements reveal a high concentration of hydrogen complexes in the form VInH4 existing in the material before annealing in agreement with recent experimental studies. It is argued that the dominant and essential process producing the semi-insulating behavior is the compensation produced by an EL2-like deep donor phosphorus antisite defect, which is formed by the dissociation of the hydrogen complexes during the process of annealing. The deep donor compensates acceptors, the majority of which are shallow residual acceptor impurities and deep hydrogen associated VIn and isolated VIn levels, produced at the first stage of the dissociation of the VInH4 complex. The high concentration of indium vacancies produced by the dissociation are the precursor of the EL2-like phosphorus antisite. These results show the importance of hydrogen on the electrical properties of InP and indicate that this largely results from low formation energy of the complex VInH4 in comparison with that of an isolated VIn. © 1998 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
81.05.Ea III-V semiconductors
81.10.Fq Growth from melts; zone melting and refining
71.55.Eq III-V semiconductors

Characterization of charged defects in CdxHg1−xTe and CdTe crystals by electron beam induced current and scanning tunneling spectroscopy

G. Panin, C. Díaz-Guerra, and J. Piqueras

Appl. Phys. Lett. 72, 2129 (1998); http://dx.doi.org/10.1063/1.121298 (3 pages) | Cited 5 times

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A correlative study of the electrically active defects of CdxHg1−xTe and CdTe crystals has been carried out using a scanning electron microscope/scanning tunneling microscope (SEM/STM) combined system. Charged structural and compositional defects were revealed by the remote electron beam induced current (REBIC) mode of the scanning electron microscope. The electronic inhomogeneities of the samples were analyzed with nm resolution by current imaging tunneling spectroscopy (CITS) measurements, which showed the existence of built-in electrostatic barriers as well as local variations of the surface band gap in the defect areas imaged by REBIC. © 1998 American Institute of Physics.
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71.55.Gs II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors

Time-resolved Raman studies of the decay of the longitudinal optical phonons in wurtzite GaN

K. T. Tsen, D. K. Ferry, A. Botchkarev, B. Sverdlov, A. Salvador, and H. Morkoc

Appl. Phys. Lett. 72, 2132 (1998); http://dx.doi.org/10.1063/1.121299 (3 pages) | Cited 60 times

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Decay of the longitudinal-optical (LO) phonons in wurtzite GaN has been studied by subpicosecond time-resolved Raman spectroscopy. Our experimental results show that among the various possible decay channels, the LO phonons in wurtzite GaN decay primarily into a large wave-vector TO and a large wave-vector LA or TA phonon. These experimental results are consistent with the recent theoretical calculations of the phonon dispersion curves for wurtzite GaN. © 1998 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors

A scanning tunneling microscopy study of atomic-scale clustering in InAsP/InP heterostructures

S. L. Zuo, W. G. Bi, C. W. Tu, and E. T. Yu

Appl. Phys. Lett. 72, 2135 (1998); http://dx.doi.org/10.1063/1.121300 (3 pages) | Cited 9 times

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We have used cross-sectional scanning tunneling microscopy to perform atomic-scale characterization of InAs0.35P0.65/InP strained-layer multiple-quantum-well structures grown by gas-source molecular-beam epitaxy. High-resolution (110) cross-sectional images reveal nanoscale clustering of As and P in the InAsxP1−x alloy layers. Boundaries between As-rich and P-rich regions in the alloy layers appear to be preferentially oriented along the [112] and [112] directions in the (110) plane, suggesting that boundaries between As-rich and P-rich clusters tend to form within {111} planes in the lattice. The nanoscale compositional variations within the InAsxP1−x alloy layers lead to an asymmetry in interface quality in the (110) cross section, with the InAsxP1−x-on-InP interfaces being much smoother and more abrupt than the InP-on-InAsxP1−x interfaces. Analysis of (110) cross-sectional images suggests that the clusters formed within the InAsxP1−x alloy are elongated along the [110] direction in the crystal. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness
61.46.-w Structure of nanoscale materials

A metal-free cathode for organic semiconductor devices

G. Parthasarathy, P. E. Burrows, V. Khalfin, V. G. Kozlov, and S. R. Forrest

Appl. Phys. Lett. 72, 2138 (1998); http://dx.doi.org/10.1063/1.121301 (3 pages) | Cited 159 times

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We introduce a class of low-reflectivity, high-transparency, nonmetallic cathodes useful for a wide range of electrically active, transparent organic devices. The metal-free cathode employs a thin film of copper phthalocyanine (CuPc) capped with a film of low-power, radio-frequency sputtered indium tin oxide (ITO). The CuPc prevents damage to the underlying organic layers during the ITO sputtering process. We present a model suggesting that damage-induced states at the cathode/organic film interface are responsible for the electron injection properties of the contact. Due to the low contact reflectivity, a non-antireflection-coated, metal-free transparent organic light-emitting device (MF-TOLED) is demonstrated with 85% transmission in the visible, emitting nearly identical amounts of light in the forward and backscattered directions. The MF-TOLED performance is found to be comparable to that of conventional TOLEDs employing a more reflective and absorptive cathode consisting of a semitransparent thin film of Mg:Ag capped with ITO. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.15.Cd Deposition by sputtering
73.61.Ph Polymers; organic compounds

Mid-infrared intersubband electroluminescence from a single-period GaAs/AlGaAs triple barrier structure

Y. B. Li, J. W. Cockburn, M. S. Skolnick, J. P. Duck, M. J. Birkett, I. A. Larkin, R. Grey, G. Hill, and M. Hopkinson

Appl. Phys. Lett. 72, 2141 (1998); http://dx.doi.org/10.1063/1.121302 (3 pages) | Cited 3 times

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This letter reports the observation of intersubband electroluminescence from a single-period resonant tunneling structure. Intersubband emission (λ ≈ 8.4 μm), with a full width at half maximum of 7 meV, was observed from a GaAs/AlGaAs triple barrier structure with quantum well widths of 66 and 33 Å. The emission was coupled out of the sample by a metallic grating with a period of 5 μm deposited on the surface. The intensity of emission follows the resonance behavior in the I–V characteristics. As the temperature increases from 10 to 200 K, the emission intensity decreases monotonically by a factor of ∼ 2 and the emission energy shifts down slightly (ΔE ≈ 2.7 meV). The temperature dependence of the emission energy is explained by a combination of thermal broadening of the electron distribution and the nonparabolicity of the conduction bands. © 1998 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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