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8 Mar 1999

Volume 74, Issue 10, pp. 1355-1498

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Self-organized In0.4Ga0.6As quantum-dot lasers grown on Si substrates

K. K. Linder, J. Phillips, O. Qasaimeh, X. F. Liu, S. Krishna, P. Bhattacharya, and J. C. Jiang

Appl. Phys. Lett. 74, 1355 (1999); http://dx.doi.org/10.1063/1.123548 (3 pages) | Cited 5 times

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We report growth of self-organized In0.4Ga0.6As quantum dots on Si substrates by molecular-beam epitaxy. Low-temperature (17 K) photoluminescence spectra show that the optical properties of In0.4Ga0.6As quantum dots grown on Si are comparable to quantum dots grown on GaAs substrates. We also present preliminary characteristics of In0.4Ga0.6As quantum-dot lasers grown on Si substrates. Light versus current measurements at 80 K under pulsed bias conditions show that Ith=3.85 kA/cm2. The lasing spectral output has a peak emission wavelength of 1.013 μm and a linewidth (full width at half maximum) of ∼4 Å at the threshold. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.66.Fd III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Threshold reduction of stimulated Brillouin scattering by the enhanced Stokes noise initiation

Hyun Su Kim, Sung-Ho Kim, Do-Kyeong Ko, Gwon Lim, Byung Heon Cha, and Jongmin Lee

Appl. Phys. Lett. 74, 1358 (1999); http://dx.doi.org/10.1063/1.123549 (3 pages) | Cited 2 times

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A method of threshold reduction for stimulated Brillouin scattering (SBS) has been demonstrated in a SBS medium combined with a laser dye. It is based on the enhanced Stokes noise initiated by additional field with a Brillouin-shifted frequency component emitted from the laser dye in the SBS medium. Rhodamine 6G dye dissolved in SBS medium (ethanol), which was pumped by a 570 nm wavelength laser, was used to prove the SBS threshold reduction by the additional Stokes fields. The SBS threshold of this solution was reduced to a level about four times lower than that of the pure SBS medium. Also, the experimental results were investigated using the modified formula for the SBS threshold. © 1999 American Institute of Physics.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
78.35.+c Brillouin and Rayleigh scattering; other light scattering
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Triplet luminescent dinuclear-gold(I) complex-based light-emitting diodes with low turn-on voltage

Yuguang Ma, Xuemei Zhou, Jiacong Shen, Hsiu-Yi Chao, and Chi-Ming Che

Appl. Phys. Lett. 74, 1361 (1999); http://dx.doi.org/10.1063/1.123550 (3 pages) | Cited 18 times

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The electroluminescence (EL) from a dinuclear-gold(I)-chlorate compound containing bridging phosphine ligands [Au2(dppm)Cl2] as emitting layer is reported. Devices with a structure Al/Au2(dppm)Cl2/indium–tin–oxide demonstrated a uniform emission under the driving voltage below 1 V. The EL emission was from triplet excited state and the emission color of the device was found to depend on the deposition rate of Au2(dppm)Cl2, which can be explained as the different aggregation forms of the stacking compound in the deposition process. © 1999 American Institute of Physics.  
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Lateral current spreading in ridge waveguide laser diodes

Martin Achtenhagen and Amos Hardy

Appl. Phys. Lett. 74, 1364 (1999); http://dx.doi.org/10.1063/1.123551 (3 pages) | Cited 11 times

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Lateral current spreading is experimentally and theoretically investigated in ridge waveguide laser diodes having various residual guide thickness outside the ridge region. It is found that a critical residual thickness exists below which the lasers emit in a single mode with a low threshold current. Above this critical value, the threshold rises rapidly and the lasers oscillate simultaneously in the two lowest order lateral modes. This critical thickness can be used to experimentally determine an average doping level of the upper waveguide layer. This doping level permits the control of the threshold current and series resistance. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

Optically pumped (GaIn)As/Ga(PAs) vertical-cavity surface-emitting lasers with optimized dynamics

C. Ellmers, M. R. Hofmann, D. Karaiskaj, S. Leu, W. Stolz, W. W. Rühle, and M. Hilpert

Appl. Phys. Lett. 74, 1367 (1999); http://dx.doi.org/10.1063/1.123552 (3 pages) | Cited 13 times

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We present a vertical-cavity surface-emitting laser structure optimized for fast intrinsic emission dynamics, using the strain-compensated (GaIn)As/Ga(PAs) material system with a 2λ sin-type cavity. The high quality of the epitaxial growth is revealed by the large normal mode splitting of 10.5 meV found in reflectivity measurements. The fast dynamical response of our structure after femtosecond optical excitation at 30 K yields a pulse width of 3.2 ps and a peak delay of only 4.8 ps. A structure designed for laser emission at higher temperatures exhibits picosecond dynamics at room temperature. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Photonic crystals for micro lightwave circuits using wavelength-dependent angular beam steering

Hideo Kosaka, Takayuki Kawashima, Akihisa Tomita, Masaya Notomi, Toshiaki Tamamura, Takashi Sato, and Shojiro Kawakami

Appl. Phys. Lett. 74, 1370 (1999); http://dx.doi.org/10.1063/1.123553 (3 pages) | Cited 121 times

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Light-beam steering that is extremely wavelength dependent has been demonstrated by using photonic crystals fabricated on Si. The scanning span reached 50° with only a 1% shift of incident wavelength at around 1 μm. The resulting angular dispersion is two orders of magnitude larger than that achieved with conventional prisms or gratings. The application of such superprism phenomena promises to enable the fabrication of integrated micro lightwave circuits that will allow more efficient use of wavelength resources when used in wavelength multiplexers/demultiplexers or dispersion compensators by enabling lower loss and broader bandwidth. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.50.-p Quantum optics
42.82.-m Integrated optics
42.79.-e Optical elements, devices, and systems
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Discontinuous phase elements for transverse mode selection in laser resonators

Ram Oron, Yochay Danziger, Nir Davidson, Asher A. Friesem, and Erez Hasman

Appl. Phys. Lett. 74, 1373 (1999); http://dx.doi.org/10.1063/1.123554 (3 pages) | Cited 22 times

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Discontinuous phase elements can be inserted into laser resonators so that the lasers will operate with only one desired high order transverse mode. These elements introduce sharp discontinuous phase changes so as to result in minimal losses for a desired transverse mode but high losses to others. The basic principles, along with experimental results with Nd:yttrium–aluminum–garnet and CO2 lasers, illustrating improved output powers with a high beam quality of low divergence, are presented. © 1999 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Lt Gas lasers including excimer and metal-vapor lasers

The influence of the p-n junction induced electric field on the optical properties of InGaN/GaN/AlGaN light emitting diode

T. Wang, T. Sugahara, S. Sakai, and J. Orton

Appl. Phys. Lett. 74, 1376 (1999); http://dx.doi.org/10.1063/1.123555 (3 pages) | Cited 4 times

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The temperature dependence of photoluminescence measurement was performed on an undoped In0.126Ga0.874N/GaN multiple quantum well (MQW) structure and a light emitting diode (LED) structure using this MQW as an active region. The emission energy of the LED structure showed a red shift of about 230 meV at room temperature compared with the undoped In0.126Ga0.874N/GaN MQW. This behavior of the LED structure is attributed to the quantum-confined Stark effect due to its p-n junction induced electric field. This conclusion was confirmed by a calculation and a detailed discussion based on the theory of the quantum-confined Stark effect. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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In situ annealing studies of molecular-beam epitaxial growth of SrS:Cu

W. Tong, Y. B. Xin, W. Park, and C. J. Summers

Appl. Phys. Lett. 74, 1379 (1999); http://dx.doi.org/10.1063/1.123556 (3 pages) | Cited 15 times

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Annealing studies are reported on molecular-beam epitaxial grown SrS:Cu which has potential as a blue phosphor for full color electroluminescent (EL) displays. It was found that annealing under a sulfur flux at 650 °C greatly improved film quality and luminescent brightness. This was attributed to the reduction of sulfur vacancies, and a large enhancement in the grain size of these thin-film phosphors. Using this procedure, EL devices with a luminance of 26 cd/m2 at 40 V above the turn-on threshold voltage with chromaticity coordinates of x = 0.17, y = 0.29 were obtained. © 1999 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.60.Fi Electroluminescence
78.66.Li Other semiconductors

Ge-related faceting and segregation during the growth of metastable (GaAs)1−x(Ge2)x alloy layers by metal–organic vapor-phase epitaxy

A. G. Norman, J. M. Olson, J. F. Geisz, H. R. Moutinho, A. Mason, M. M. Al-Jassim, and S. M. Vernon

Appl. Phys. Lett. 74, 1382 (1999); http://dx.doi.org/10.1063/1.123557 (3 pages) | Cited 11 times

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(GaAs)1−x(Ge2)x alloy layers, 0<x<0.22, have been grown by metal–organic vapor-phase epitaxy on vicinal (001) GaAs substrates. Transmission electron microscopy revealed pronounced phase separation in these layers, resulting in regions of GaAs-rich zinc-blende and Ge-rich diamond cubic material that appears to lead to substantial band-gap narrowing. For x = 0.1 layers, the phase-separated microstructure consisted of intersecting sheets of Ge-rich material on {115}B planes surrounding cells of GaAs-rich material, with little evidence of antiphase boundaries. Atomic force microscopy revealed {115}B surface faceting associated with the phase separation. © 1999 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.75.-g Phase equilibria

Photorefractive properties of potassium lithium niobate crystals

Changxi Yang, Youting Song, Daofan Zhang, Xiaomin Wang, Tang Zhou, Feidi Fan, and Xing Wu

Appl. Phys. Lett. 74, 1385 (1999); http://dx.doi.org/10.1063/1.123558 (3 pages) | Cited 1 time

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We report the photorefractive properties of K3Li2−xNb5+xO15+2x crystals grown by the edge-defined, film-fed technique. The crystals with lithium/niobate ratio from 18.5/51.5 to 26/44 are grown and investigated by two-beam coupling technique. The crystal of composition K3Li1.783Nb5.687O16.61 exhibits an intensity coupling constant of 8 cm−1 and an effective trap density of 1.8×1022 m−3. The photorefractive majority carriers are electrons in as-grown crystals. The grating recording time and erasure time are 530 and 260 ms, respectively, at an intensity of 2 W/cm2. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ln Holographic recording materials; optical storage media
81.10.Fq Growth from melts; zone melting and refining
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Growth mode and strain relaxation of InAs on InP (111)A grown by molecular beam epitaxy

Hanxuan Li, Theda Daniels-Race, and Zhanguo Wang

Appl. Phys. Lett. 74, 1388 (1999); http://dx.doi.org/10.1063/1.123559 (3 pages) | Cited 7 times

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Growth mode and strain relaxation of molecular-beam-epitaxy grown InAs/InAlAs/InP (111)A system have been investigated using reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence measurements. In direct contrast to the well-studied InAs/GaAs system, our experimental results show that the InAs grown on InAlAs/InP (111)A follows the Stranski–Krastanov mode. Both self-organized InAs quantum dots and relaxed InAs islands are formed depending on the InAs coverage. Intense luminescence signals from both the InAs quantum dots and wetting layer are observed. The luminescence efficiency of (111)A samples is comparable to that of (001) samples, suggesting the feasibility of fabricating quantum dot optoelectronic devices on InP (111)A surfaces. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)

Bi: Perfect surfactant for Ge growth on Si(111)?

T. Schmidt, J. Falta, G. Materlik, J. Zeysing, G. Falkenberg, and R. L. Johnson

Appl. Phys. Lett. 74, 1391 (1999); http://dx.doi.org/10.1063/1.123560 (3 pages) | Cited 17 times

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We have investigated the growth of Ge on Bi-terminated Bi:Si(111)-√×√. In-situ measurements of x-ray standing waves, crystal truncation rods and scanning tunneling microscopy clearly show that, at substrate temperatures around 485 °C, smooth and homogeneous Ge films of thicknesses exceeding 30 bilayers Ge can be grown. For Ge coverages larger than 10 bilayers, the Ge film is completely relaxed. Bi is found to segregate to the surface during Ge deposition, and can be removed from the surface after growth by mild annealing at 520 °C as proven by Auger electron spectroscopy. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Effect of growth conditions on surface morphology and photoelectric work function characteristics of iridium oxide thin films

Babu R. Chalamala, Yi Wei, Robert H. Reuss, Sanjeev Aggarwal, Bruce E. Gnade, R. Ramesh, John M. Bernhard, Edward D. Sosa, and David E. Golden

Appl. Phys. Lett. 74, 1394 (1999); http://dx.doi.org/10.1063/1.123561 (3 pages) | Cited 35 times

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The effect of thermal growth conditions on the morphology and surface work function of iridium oxide thin films grown by annealing Ir thin films in an O2 ambient is presented. The samples were analyzed using x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and photoelectric work function measurements. It is found that, with increasing temperature, IrO2 changes from (110) oriented to a mixture of (110) and (200) during the oxide growth. This is manifested as a sharpening of the photoelectric energy distributions at 800 °C. The surface work function was determined to be 4.23 eV using ultraviolet photoelectron spectroscopy. X-ray photoelectron spectroscopy analysis shows that IrO2 starts to form at 600 °C accompanied by surface roughening. Annealing the Ir film at 900 °C in O2 ambient leads to almost complete desorption of the film. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
79.60.Jv Interfaces; heterostructures; nanostructures
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

A monohydride high-index silicon surface: Si(114):H-(2×1)

A. Laracuente, S. C. Erwin, and L. J. Whitman

Appl. Phys. Lett. 74, 1397 (1999); http://dx.doi.org/10.1063/1.123562 (3 pages) | Cited 8 times

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We describe the adsorption of H on Si(114)-(2×1) as characterized by scanning tunneling microscopy and first-principles calculations. Like Si(001)—and despite the relative complexity of the (114) structure—a well-ordered, low-defect-density monohydride surface forms at ∼ 400 °C. Surprisingly, the clean surface reconstruction is essentially maintained on the (2×1) monohydride surface, composed of dimers, rebonded double-layer steps, and nonrebonded double-layer steps, with each surface atom terminated by a single H. This H-passivated surface can also be easily and uniformly patterned by selectively desorbing the H with low-voltage electrons. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Mobility enhancement through homogeneous nematic alignment of a liquid-crystalline polyfluorene

M. Redecker, D. D. C. Bradley, M. Inbasekaran, and E. P. Woo

Appl. Phys. Lett. 74, 1400 (1999); http://dx.doi.org/10.1063/1.123563 (3 pages) | Cited 79 times

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Homogeneous alignment of poly(9,9′-dioctylfluorene) films on rubbed polyimide results in a more than one order of magnitude increase in time-of-flight hole mobility normal to the alignment direction. We find μ = 8.5±1×10−3 cm2/V s at an electric field of E = 104 V/cm. Hole transport is found to be nondispersive, indicating a low degree of energetic disorder. © 1999 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Short-wavelength photoluminescence from silicon and nitrogen coimplanted SiO2 films

J. Zhao, D. S. Mao, Z. X. Lin, X. Z. Ding, B. Y. Jiang, Y. H. Yu, X. H. Liu, and G. Q. Yang

Appl. Phys. Lett. 74, 1403 (1999); http://dx.doi.org/10.1063/1.123564 (3 pages) | Cited 8 times

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Intense short-wavelength photoluminescence (PL) observed at room temperature from thermal SiO2 films implanted with Si and N is reported. A flat Si profile was first created. N ions were subsequently implanted into the same depth region as the implanted Si ions. Two PL bands peaking at ∼330 and ∼430 nm were observed from the samples at room temperature with and without annealing. It is found that the PL has a strong dependence on the stabilized N in the Si- and N-coimplanted SiO2 films. The PL may originate from a complex of Si, N, and O. © 1999 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Effects of stress on the growth of TiSi2 thin films on (001)Si

S. L. Cheng, H. Y. Huang, Y. C. Peng, L. J. Chen, B. Y. Tsui, C. J. Tsai, and S. S. Guo

Appl. Phys. Lett. 74, 1406 (1999); http://dx.doi.org/10.1063/1.123565 (3 pages) | Cited 7 times

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Tensile stress induced by backside CoSi2 films on a silicon substrate has been found to enhance the growth of C54–TiSi2 on (001)Si. In contrast, compressive stress induced by backside oxide films on the silicon substrate was found to retard significantly the growth of C54–TiSi2 on (001)Si. For Ti on stressed (001)Si after rapid thermal annealing at 800 °C for 30 s, the thickness of the C54– TiSi2 films was found to increase and decrease with the tensile and compressive stress levels, respectively. The retarded growth is attributed to the hindrance of the migration of Si through the Ti/Si interface by the compressive stress. On the other hand, the presence of tensile stress promotes the Si diffusion to facilitate the formation of Ti silicide thin films. © 1999 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
66.30.Ny Chemical interdiffusion; diffusion barriers
85.40.Ls Metallization, contacts, interconnects; device isolation
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Intersubband electroluminescence in InAs/GaSb/AlSb type-II cascade structures

K. Ohtani and H. Ohno

Appl. Phys. Lett. 74, 1409 (1999); http://dx.doi.org/10.1063/1.123566 (3 pages) | Cited 10 times

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Intersubband electroluminescence in InAs quantum wells embedded in InAs/GaSb/AlSb type-II cascade structures is reported. The observed emission energy is in good agreement with calculation based on the multiband k⋅p theory. Dominant polarization of the emitted light is perpendicular to the quantum well layers. Difference in the spectrum shape between intersubband and interband cascade transitions is also presented. © 1999 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors

One-dimensional to one-dimensional electron resonant tunneling in a double asymmetric quantum-wire structure

Yongqiang Wang, Qi Huang, and Junming Zhou

Appl. Phys. Lett. 74, 1412 (1999); http://dx.doi.org/10.1063/1.123567 (3 pages) | Cited 4 times

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An atomically precise double asymmetric quantum-wire structure was fabricated with the cleaved edge overgrowth method. A resonant tunneling diode for such a structure was successfully achieved. Its voltage–current characteristic was measured at 77 K. A sharp resonant tunneling current peak was observed and its peak-to-valley ratio is about 18:1, which is much larger than that of a double-barrier quantum-well structure, and it is ascribed to one-dimensional to one-dimensional electron resonant tunneling through the double asymmetric quantum-wire structure. © 1999 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.-r Electrical properties of specific thin films
85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Antimonides with the half-Heusler structure: New thermoelectric materials

K. Mastronardi, D. Young, C.-C. Wang, P. Khalifah, R. J. Cava, and A. P. Ramirez

Appl. Phys. Lett. 74, 1415 (1999); http://dx.doi.org/10.1063/1.123596 (3 pages) | Cited 52 times

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The thermoelectric properties near ambient temperature of half-Heusler alloys based on LnPdSb, where Ln=Ho, Er, and Dy are reported. The Seebeck coefficients are large, between 60 and 250 μV/K, and the materials are p type. The resistivities are between 0.6 and 20 mΩ cm. Thermal conductivities are between approximately 5.0 and 3.5 W/mK at 300 K, and are smallest in intentionally disordered materials. The highest ambient temperature ZT obtained is 0.06. Band-structure calculations are presented for LuPdSb. It is suggested that half-Heusler alloys with 18 electrons per formula unit may represent a large class of thermoelectric materials. © 1999 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Pump and probe measurement of intersubband relaxation time in short-wavelength intersubband transition

Takashi Asano, Susumu Noda, and Katsuhiro Tomoda

Appl. Phys. Lett. 74, 1418 (1999); http://dx.doi.org/10.1063/1.123568 (3 pages) | Cited 9 times

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Population relaxation dynamics of the short-wavelength (∼2.5 μm) intersubband transition (ISB-T) in narrow InGaAs/AlAs quantum wells is investigated. Femtosecond (∼100 fs) pump and probe measurement yields a relaxation time of ∼2.7 ps, which is as fast as those observed for 10–5 μm ISB-T (0.7–1.5 ps, respectively). The ISB relaxation time increases more rapidly than that predicted from the usual intersubband optical-phonon scattering model as the ISB-T energy increases. Our theoretical calculation, which takes into account the intrasubband energy relaxation process, agrees well with the experimental results. The intrasubband energy relaxation process is found to be important in the short-wavelength region. © 1999 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
63.20.K- Phonon interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Spatially resolved dopant profiling of patterned Si wafers by bias-applied phase-imaging tapping-mode atomic force microscopy

M. W. Nelson, P. G. Schroeder, R. Schlaf, B. A. Parkinson, C. W. Almgren, and A. N. Erickson

Appl. Phys. Lett. 74, 1421 (1999); http://dx.doi.org/10.1063/1.123569 (3 pages) | Cited 5 times

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Tapping-mode atomic force microscopy was used to spatially resolve areas of different doping types on Si wafers patterned by photolithography and subsequent ion implantation. Application of a direct current dc bias between cantilever and sample during measurement induced a change in the tapping-mode phase contrast depending on the dopant type of the scanned sample area. This allowed the direct identification of areas of different doping types. Additional measurements on Au samples demonstrate a direct correlation between bias-induced Coulomb force and resulting phase change allowing the conclusion that the observed phase contrast results from dc bias-induced band bending changes. © 1999 American Institute of Physics.
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
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
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.40.Hp Lithography, masks and pattern transfer
81.05.Cy Elemental semiconductors

Interface and bulk defects in SiC/GaN heterostructures characterized using thermal admittance spectroscopy

H. Witte, A. Krtschil, M. Lisker, J. Christen, M. Topf, D. Meister, and B. K. Meyer

Appl. Phys. Lett. 74, 1424 (1999); http://dx.doi.org/10.1063/1.123570 (3 pages) | Cited 3 times

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SiC/GaN p-n and n-n heterostructures grown by low pressure chemical vapor deposition were investigated using thermal admittance spectroscopy. Different kinds of defects were isolated and located. Evidence of a distribution of defects at the p-SiC/n-GaN interface is given as having thermal activation energies of (87±3) meV at 5 V and (72±4) meV at 8 V bias. Additionally, three bulk defects with activation energies between 155 and 175 meV were found. By comparison with admittance spectra of the p-type SiC substrate, one level was identified as Al acceptor in SiC, whereas the other defects are electron traps in the GaN layer. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.61.Le Other inorganic semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Nonlinear 1/f noise characteristics in luminescent porous silicon

I. Bloom and I. Balberg

Appl. Phys. Lett. 74, 1427 (1999); http://dx.doi.org/10.1063/1.123571 (3 pages) | Cited 12 times

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We present noise characteristics of luminescent porous silicon and show that they shed light on the transport mechanism in this system. The 1/f fluctuations show non-Gaussian and nonlinear behavior, and they give a high Hooge factor, typical of disordered conductors. By carrying out the measurements under various bias conditions, we found a bias-dependent redistribution of the percolating current paths. The close resemblance between the present results and those found in granular metals suggests that a tunneling process controlled by the electrostatic energy determines the conduction paths between the nanocrystallites in luminescent porous silicon. © 1999 American Institute of Physics.
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72.80.Cw Elemental semiconductors
72.70.+m Noise processes and phenomena
72.20.Ht High-field and nonlinear effects
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