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15 May 2000

Volume 76, Issue 20, pp. 2815-2963

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Metallization scheme for highly low-resistance, transparent, and thermally stable Ohmic contacts to p-GaN

Ja-Soon Jang, Seong-Ju Park, and Tae-Yeon Seong

Appl. Phys. Lett. 76, 2898 (2000); http://dx.doi.org/10.1063/1.126510 (3 pages) | Cited 38 times

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We report on a promising metallization scheme for high-quality Ohmic contacts to surface-treated p-GaN:Mg (2–3×1017 cm−3). It is shown that the as-deposited Pt/Ru contact produces a specific contact resistance of 7.8(±2.2)×10−4 Ω cm2. However, annealing of the contact at 600 °C for 2 min results in a resistance of 2.2(±2.0)×10−6 Ω cm2. It is also shown that the light transmittance of the annealed contact is 87.3% at 470 nm. Furthermore, the surface of the contact annealed at 600 °C for 30 min is found to be very smooth with a rms roughness of 0.8 nm. These results strongly indicate that the Pt/Ru can be a suitable scheme for the fabrication of high-performance laser diodes or other devices. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
81.05.Ea III-V semiconductors
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Highly monodisperse polymer-capped ZnO nanoparticles: Preparation and optical properties

Lin Guo, Shihe Yang, Chunlei Yang, Ping Yu, Jiannong Wang, Weikun Ge, and George K. L. Wong

Appl. Phys. Lett. 76, 2901 (2000); http://dx.doi.org/10.1063/1.126511 (3 pages) | Cited 157 times

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We report the preparation of highly monodisperse ZnO nanoparticles using poly(vinyl pyrrolidone) (PVP) as the capping molecules. The surface-modified ZnO nanoparticles were found to be remarkably stable. The optical absorption shows distinct excitonic features. Markedly enhanced near-band-edge ultraviolet photoluminescence and significantly reduced defect-related green emission were also observed. We attribute this observation to the nearly perfect surface passivation of the ZnO nanoparticles by the PVP molecules. The third-order nonlinear optical response of these PVP-capped ZnO nanoparticles in a dilute solution was found to be significantly larger (by at least two orders of magnitude) than that of the bulk ZnO. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
81.05.Dz II-VI semiconductors
81.05.Qk Reinforced polymers and polymer-based composites
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.65.Rv Passivation
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.-k Nonlinear optics

Effect of the Coulomb interaction on the response time and impedance of the resonant-tunneling diodes

Michael N. Feiginov

Appl. Phys. Lett. 76, 2904 (2000); http://dx.doi.org/10.1063/1.126512 (3 pages) | Cited 9 times

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We demonstrated that the response time of the resonant-tunneling structures (τresp) can be much smaller as well as much larger than the quasibound-state lifetime. A simple analytical expression for the impedance of the resonant-tunneling diode has been derived, it takes into account the Coulomb interaction and the quasibound-state lifetime. A simple equation relating τresp to the static differential conductance has also been obtained; it allows one to get τresp in the static measurements of the current–voltage curve. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Investigation of the cleaved surface of a p–i–n laser using Kelvin probe force microscopy and two-dimensional physical simulations

F. Robin, H. Jacobs, O. Homan, A. Stemmer, and W. Bächtold

Appl. Phys. Lett. 76, 2907 (2000); http://dx.doi.org/10.1063/1.126513 (3 pages) | Cited 34 times

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We have investigated the cross-sectional electric field and potential distribution of a cleaved n+-InP/InGaAsP/p+-InP p–i–n laser diode using Kelvin probe force microscopy (KFM) with a lateral resolution reaching 50 nm. The powerful characterization capabilities of KFM were compared with two-dimensional (2D) physics-based simulations. The agreement between simulations and KFM measurements regarding the main features of the electric field and potential is very good. However, the KFM yields a voltage drop between n-and p-doped InP regions which is 0.4 times the one simulated. This discrepancy is explained in terms of surface traps due to the exposure of the sample to the air and in terms of incomplete ionization. This hypothesis is confirmed by the 2D simulations. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
42.55.Px Semiconductor lasers; laser diodes

Large and stable field-emission current from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy

Makoto Kasu and Naoki Kobayashi

Appl. Phys. Lett. 76, 2910 (2000); http://dx.doi.org/10.1063/1.126514 (3 pages) | Cited 23 times

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We report on the electron field emission (FE) from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy. We found that, as the Si-dopant density increases, the threshold electric field decreases and, consequently, the FE current from AlN increases drastically. We show that heavily Si-doped (2.5×1020 cm−3) AlN has a threshold electric field of 34 V/μm, a maximum FE current density of 4.8 mA/cm2, and stable FE current (fluctuation: 3%). © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

Magnetic-field effects on undriven chaos in a weakly coupled GaAs/AlAs superlattice

K. J. Luo, K.-J. Friedland, H. T. Grahn, and K. H. Ploog

Appl. Phys. Lett. 76, 2913 (2000); http://dx.doi.org/10.1063/1.126515 (3 pages) | Cited 2 times

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We have investigated the effect of a perpendicular magnetic field on the spontaneous current oscillations in a weakly coupled GaAs/AlAs superlattice. At zero magnetic field, voltage regions of periodic as well as chaotic oscillations are observed. With increasing magnetic field B, the voltage regions for chaotic oscillations become larger and those for periodic oscillations smaller. At B=9 T, the whole voltage range consists of chaotic oscillations. At the same time, the time-averaged current–voltage characteristic hardly changes. The experimental observations demonstrate that the quantization by the perpendicular magnetic field results in an equalization of the sequential resonant tunneling process over the whole superlattice, suppressing scattering effects due to disorder. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
05.45.-a Nonlinear dynamics and chaos
73.23.-b Electronic transport in mesoscopic systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Characterization of electron trap states due to InAs quantum dots in GaAs

C. Walther, J. Bollmann, H. Kissel, H. Kirmse, W. Neumann, and W. T. Masselink

Appl. Phys. Lett. 76, 2916 (2000); http://dx.doi.org/10.1063/1.126516 (3 pages) | Cited 23 times

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InAs quantum dots grown in a GaAs matrix are investigated using capacitive transient spectroscopy and transmission electron microscopy (TEM). Two deep levels are detected which are energetically too deep to be the intrinsic electron levels of the quantum dots. Both TEM as well as the detailed non-exponential behavior of the electron capture indicate that the traps do not result from dislocations in the GaAs matrix. We propose that the measured trap levels are due to point defects in or near the quantum dots. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
61.72.J- Point defects and defect clusters

Critical size for localization of the L-like conduction states in InAs quantum dots grown on GaAs

J. A. Prieto, G. Armelles, J. M. García, L. González, A. San Paulo, and R. García

Appl. Phys. Lett. 76, 2919 (2000); http://dx.doi.org/10.1063/1.126855 (3 pages)

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The localization of the L-like conduction states is found to change from the islands to the substrate in InAs quantum dots grown on GaAs as the island-size decreases. This is due to a size-induced modification of the strain state of the islands. The critical size should correspond to dislocation formation. As a result, small InAs islands coherently strained to GaAs exhibit optical properties markedly different from those of bulk InAs. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Ea III-V semiconductors
73.20.Fz Weak or Anderson localization
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.)
78.66.Fd III-V semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
81.07.-b Nanoscale materials and structures: fabrication and characterization

Conductance quantization in nanoscale vertical structure silicon field-effect transistors with a wrap gate

K. Nishiguchi and S. Oda

Appl. Phys. Lett. 76, 2922 (2000); http://dx.doi.org/10.1063/1.126517 (3 pages) | Cited 13 times

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Experimental results of quantum ballistic transport in single quantum contact by using vertical structure silicon field effect transistors with a wrap gate are presented. Based on dc measurement, the conductance–voltage characteristics show quantized plateaus at multiples of 2e2/h. The devices were prepared by electron beam lithography and by combinations of various types of etching. The channel is fabricated by the chemical vapor deposition of amorphous silicon and solid-phase crystallization. The vertical structure allows a channel length as short as 30 nm, which is defined by the film thickness. The effective channel is reduced by the depletion potential, resulting in a much narrower channel width compared to the geometrical width of 60 nm. Thus, the effective size of the silicon transistor is smaller than the elastic mean free path of 40 nm, resulting in the conduction quantization at 3–5 K. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
85.35.Ds Quantum interference devices
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
85.40.Hp Lithography, masks and pattern transfer
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