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6 Aug 2001

Volume 79, Issue 6, pp. 705-888

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Spatial variation of electrical properties in lateral epitaxially overgrown GaN

J. W. P. Hsu, M. J. Matthews, D. Abusch-Magder, R. N. Kleiman, D. V. Lang, S. Richter, S. L. Gu, and T. F. Kuech

Appl. Phys. Lett. 79, 761 (2001); http://dx.doi.org/10.1063/1.1388877 (3 pages) | Cited 11 times

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Using confocal Raman and scanning probe microscopies, we show that the electrical properties of lateral epitaxial overgrown GaN films vary at the submicron scale. Wing regions, which are located directly above the SiOx stripes, contain carrier densities ∼ 1020 cm−3, but possess a Fermi level deep in the band gap. This cannot be explained by having a high density of free electrons in the conduction band, but is consistent with high levels of compensation and impurity band transport. In the coalescence region, stripes of different electrical properties are evident, indicating the incorporation of impurities and defects being dictated by the growth dynamics. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
71.20.Nr Semiconductor compounds

Femtosecond response time in beryllium-doped low-temperature-grown GaAs/AlAs multiple quantum wells

Tsuyoshi Okuno, Yasuaki Masumoto, Yasushi Sakuma, Yuuichi Hayasaki, and Hiroshi Okamoto

Appl. Phys. Lett. 79, 764 (2001); http://dx.doi.org/10.1063/1.1390478 (3 pages) | Cited 8 times

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We have investigated optical nonlinearity in beryllium-doped low-temperature (LT) molecular-beam-epitaxy-grown GaAs/AlAs multiple quantum wells (MQWs). The response time of the nonlinearity is reduced by Be doping in the MQW. While the undoped LT MQW shows a 0.7–0.9 ps response, the response time of the Be-doped LT MQW is as short as 0.25 ps. The saturation density of the Be-doped MQW is almost the same as that of the undoped MQW, and is smaller than that of bulk GaAs. These results demonstrate that the Be-doped LT MQW exhibits a faster response than the undoped LT MQW, and a faster response as well as larger nonlinearity than LT bulk GaAs. © 2001 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
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.47.-p Spectroscopy of solid state dynamics

Si/6H–SiC(0001): An unexpected cubic 4×3 Si phase overlayer

F. Amy, H. Enriquez, P. Soukiassian, C. Brylinski, A. Mayne, and G. Dujardin

Appl. Phys. Lett. 79, 767 (2001); http://dx.doi.org/10.1063/1.1389510 (3 pages) | Cited 9 times

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We investigate Si deposition on the 6H–SiC(0001) 3×3 surface reconstruction by atom-resolved scanning tunneling microscopy. Upon thermal annealing, the Si thin film forms an unexpected structure having dimer rows in a cubic 4×3 surface array. Such a 4×3 Si phase has a very open surface very likely being at the origin of the exceptionally high reactivity to oxygen of the Si/6H–SiC(0001) system. These findings are relevant in silicon carbide oxidation. © 2001 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing

Ultrafast impulsive excitation of coherent longitudinal acoustic phonon oscillations in highly photoexcited InSb

M. D. Cummings and A. Y. Elezzabi

Appl. Phys. Lett. 79, 770 (2001); http://dx.doi.org/10.1063/1.1389836 (3 pages) | Cited 8 times

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We report on the direct time-resolved measurement of high-frequency coherent longitudinal acoustic (LA) phonon oscillations in InSb. Two LA-phonon modes are impulsively generated in a highly photoexcited InSb sample and detected through reflectivity modulation with a temporal resolution of 15 fs. The measured frequencies, νLA(L1) = 4.34 THz and νLA(X3) = 3.75 THz, are in excellent agreement with those obtained through time-independent techniques. A frequency redshift in the LA(L1)-phonon frequency, as the energy fluence is increased beyond 10% of the damage threshold fluence, is attributed to an anisotropic impulsive softening of the InSb lattice. © 2001 American Institute of Physics.
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63.20.K- Phonon interactions
78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors

Ultrasensitive Si phototransistors with a punchthrough base

Hailin Luo, Yuchun Chang, K. S. Wong, and Y. Wang

Appl. Phys. Lett. 79, 773 (2001); http://dx.doi.org/10.1063/1.1390477 (3 pages) | Cited 2 times

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Si phototransistors with a punchthrough base were fabricated with regular planar technology. Optical conversion gains larger than 15 000 were observed. In addition to very high gain, the unique structure of the device also resulted in a fast transient response as well as low output noise. The measured full width at half maximum of the device transient response is 1.6 ns and a −3 dB bandwidth of 300 MHz. The measured output noises at different currents can be well fitted by the relation math = 2qIC. © 2001 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Oxygen exchange kinetics on a highly oriented La0.5Sr0.5CoO3−δ thin film prepared by pulsed-laser deposition

Yuemei L. Yang, A. J. Jacobson, C. L. Chen, G. P. Luo, K. D. Ross, and C. W. Chu

Appl. Phys. Lett. 79, 776 (2001); http://dx.doi.org/10.1063/1.1390316 (3 pages) | Cited 32 times

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Oxygen exchange at a highly oriented La0.5Sr0.5CoO3−δ thin film prepared on (100) surfaces of an yttria-stabilized zirconia single crystal by pulsed-laser deposition was studied with ac impedance spectroscopy under various temperatures and oxygen partial pressures. Three distinctive features observed in the impedance spectra were assigned to contributions from the ionic conduction of the electrolyte, oxide ion transfer across the electrode/electrolyte interface, and the oxygen exchange on the film surface. An equivalent circuit model was proposed to analyze the impedance results, from which the surface chemical exchange coefficients, kchem, were derived as a function of temperature and oxygen partial pressure. © 2001 American Institute of Physics.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
66.30.H- Self-diffusion and ionic conduction in nonmetals
81.15.Fg Pulsed laser ablation deposition
82.45.Mp Thin layers, films, monolayers, membranes

Spatial distribution of space charge in conjugated polymers

F. Feller, D. Geschke, and A. P. Monkman

Appl. Phys. Lett. 79, 779 (2001); http://dx.doi.org/10.1063/1.1391399 (3 pages) | Cited 15 times

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We demonstrate the pyroelectric effect in a conjugated polymer, poly(2,5-pyridinediyl) (PPY), and we use the laser intensity modulation method (LIMM) to resolve the spatial distribution of electric field and space charges inside a 5 μm Au/PPY/Au sandwich device. The pyroelectric signal shows hysteresis behavior with respect to the applied bias indicating permanent storage of injected charges. From the analysis of the LIMM spectra we conclude that application of a bias leads to the accumulation of space charges near the electrodes, while a zone of opposite space charge may establish in a distance of about 1 μm from it. The charged state retains after removing the bias and can lead to an internal electric field that is opposite to the external poling field in the bulk of the polymer film. © 2001 American Institute of Physics.
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77.22.Jp Dielectric breakdown and space-charge effects
77.84.Jd Polymers; organic compounds
73.61.Ph Polymers; organic compounds
77.70.+a Pyroelectric and electrocaloric effects

Direct-to-indirect band gap crossover for the BexZn1−xTe alloy

O. Maksimov and M. C. Tamargo

Appl. Phys. Lett. 79, 782 (2001); http://dx.doi.org/10.1063/1.1390327 (3 pages) | Cited 19 times

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We have investigated the growth and optical properties of a set of BexZn1−xTe epitaxial layers having different composition, with x ranging from 0–0.7. Comparison of the reflectivity and the photoluminescence spectra allowed us to locate the direct-to-indirect band gap crossover for this alloy at x ≈ 0.28. The Γ→Γ direct band gap exhibits a linear dependence on composition over the entire compositional range and can be fitted to the equation EΓg(x) = 2.26∗(1−x)+4.1∗x. It increases linearly with BeTe content at a rate of 18 meV for a change of 1% in BeTe content. The Γ→X indirect band gap for BexZn1−xTe can be fitted to the equation EXg(x) = 3.05∗(1−x)+2.8∗x−0.5∗x∗(1−x), suggesting that the energy of the indirect Γ→X transition for ZnTe is about 3.05 eV. © 2001 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
68.55.Nq Composition and phase identification
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Aluminum-doped n-type ZnTe layers grown by molecular-beam epitaxy

J. H. Chang, T. Takai, B. H. Koo, J. S. Song, T. Handa, and T. Yao

Appl. Phys. Lett. 79, 785 (2001); http://dx.doi.org/10.1063/1.1390481 (3 pages) | Cited 25 times

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N-type ZnTe layers with high electron concentration are grown by molecular-beam epitaxy using aluminum as the donor species. The ZnTe:Al layers show a high structural quality with a narrow x-ray diffraction linewidth (24 arcsec) and a high carrier concentration up to n = 4×1018 cm−3 with low resistivity (ρ=0.017 Ω cm). The dependence of the electron mobility on the carrier concentration suggests that the dominant scattering mechanisms in the ZnTe:Al layers are ionized impurity scattering and polar optical phonon scattering. The photoluminescence spectrum of moderately doped ZnTe layers shows strong Al–donor-related bound exciton lines: I2 (2.378 eV) and donor–acceptor pair emission (zero phonon energy=2.324 eV) with a weak deep-level emission (2.19 eV). Highly Al-doped layers show an increase in the deep-level emission intensity and a decrease in carrier mobility, which are interpreted in terms of the increase in the carrier compensation. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors

Transport through a nine period silicon/oxygen superlattice

Yong-Jin Seo, John C. Lofgrene, and Raphael Tsu

Appl. Phys. Lett. 79, 788 (2001); http://dx.doi.org/10.1063/1.1394162 (3 pages)

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The silicon/adsorbed oxygen superlattice was introduced as an epitaxial barrier for silicon quantum devices. A barrier height of ∼0.5 eV with a thin layer of silicon sandwiched between two adsorbed oxygen layers has been achieved. This work describes a similar structure with nine periods which may serve as a replacement of the present amorphous silicon dioxide gate for metal oxide semiconductor field effect transistor. The insulating property derived from our current–voltage (I–V) and conductance–voltage (G–V) measurements indicates that the scheme may serve as a replacement of silicon on insulator. © 2001 American Institute of Physics.
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73.63.Rt Nanoscale contacts
85.35.Ds Quantum interference devices
73.23.-b Electronic transport in mesoscopic systems
85.30.Tv Field effect devices
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Localized charge injection in SiO2 films containing silicon nanocrystals

Elizabeth A. Boer, Mark L. Brongersma, Harry A. Atwater, Richard C. Flagan, and L. D. Bell

Appl. Phys. Lett. 79, 791 (2001); http://dx.doi.org/10.1063/1.1383574 (3 pages) | Cited 41 times

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An atomic-force microscope (AFM) is used to locally inject, detect, and quantify the amount and location of charge in SiO2 films containing Si nanocrystals (size ∼2–6 nm). By comparison with control samples, charge trapping is shown to be due to nanocrystals and not ion-implantation-induced defects in samples containing ion-beam-synthesized Si nanocrystals. Using an electrostatic model and AFM images of charge we have estimated the amount of charge injected in a typical experiment to be a few hundred electrons and the discharge rate to be ∼35±15 e/min. © 2001 American Institute of Physics.
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73.61.Ng Insulators
71.55.Ht Other nonmetals
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.05.Cy Elemental semiconductors
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.65.Hb Quantum dots (patterned in quantum wells)
73.63.Kv Quantum dots
81.07.Ta Quantum dots
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.-c Methods of micro- and nanofabrication and processing
68.37.Ps Atomic force microscopy (AFM)
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
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