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22 Jun 1998

Volume 72, Issue 25, pp. 3243-3383

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Uniform component of index structure induced in Ge-SiO2 fibers by spatially modulated ultraviolet light

Tsung-Ein Tsai, Glen M. Williams, and E. J. Friebele

Appl. Phys. Lett. 72, 3243 (1998); http://dx.doi.org/10.1063/1.121678 (3 pages) | Cited 8 times

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Experimental data are presented to show that Ge(1) and Ge(2) centers are induced by trapping photoinduced electrons from the conduction band, in agreement with our previous proposal that both are trapped electron centers. The spacing (Λ) dependence of ultraviolet (UV) light bleaching of the pre-existing Ge E′ centers illustrates that the electron diffusion length is greater than Λ of the spatially modulated UV light used in the fabrication of fiber Bragg gratings (FBGs) with Bragg wavelengths ⩽ 1.5 μm (short period grating) for laser powers as low as 25 mJ/cm2. The Ge(1) and Ge(2) centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs.
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42.81.Wg Other fiber-optical devices
42.79.Dj Gratings
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.55.-i Impurity and defect levels

1.5 μm asymmetric Fabry–Perot modulators with two distinct modulation and chirp characteristics

S. J. B. Yoo, M. A. Koza, Raj Bhat, and Catherine Caneau

Appl. Phys. Lett. 72, 3246 (1998); http://dx.doi.org/10.1063/1.121612 (3 pages) | Cited 6 times

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This letter discusses the design and the realization of asymmetric Fabry–Perot modulators with InP/InGaAsP distributed Bragg reflectors and 80 AlInGaAs quantum wells. We demonstrate two types of modulators utilizing two different top reflectors: an InP to air interface and a Si/SiO2/Si coating. The first modulator showed a monotonic reduction in the reflectivity as the bias voltage increased, and achieved a 2.2 dB insertion loss and a 15 dB contrast ratio at the resonant wavelength. The second modulator showed an initial reduction and then an increase in the reflectivity as the bias changed from 0 to −10 V. The chirp calculation based on the measured data reveals that the second modulator exhibits two distinct positive and negative chirp characteristics. © 1998 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Dispersion correction of surface-normal optical interconnection using two compensated holograms

Charles C. Zhou, Zhenhai Fu, Ray T. Chen, and Brian M. Davies

Appl. Phys. Lett. 72, 3249 (1998); http://dx.doi.org/10.1063/1.121613 (3 pages) | Cited 3 times

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Performance of optical interconnects using volume holographic gratings and substrate-guided waves is subject to source wavelength detuning which originates from laser chirping and operating temperature changes. In this letter, we characterize and measure the dispersion of commonly used surface-normal volume holographic gratings. Dispersion characteristics of a 20 μm thick photopolymer volume holographic grating are evaluated. A dispersion correction method is demonstrated to provide a dispersion-free surface-normal optical interconnect using two dispersion-compensated volume holographic gratings and substrate-guided waves which automatically compensate the dispersion that results from detuning over a 5.7 nm bandwidth. © 1998 American Institute of Physics.
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42.82.Ds Interconnects, including holographic interconnects
42.40.Eq Holographic optical elements; holographic gratings
42.60.Fc Modulation, tuning, and mode locking

Inducing a large second-order optical nonlinearity in soft glasses by poling

F. C. Garcia, I. C. S. Carvalho, E. Hering, W. Margulis, and B. Lesche

Appl. Phys. Lett. 72, 3252 (1998); http://dx.doi.org/10.1063/1.121614 (3 pages) | Cited 21 times

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Electrothermal poling of soft glasses (soda lime and borosilicate glass) at relatively high currents led to the creation of a second-order optical nonlinearity. The second-harmonic generation efficiency decays in time, and the decay rate can be accelerated by exposure to intense infrared radiation. © 1998 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Coupled-power theory of nonlinear distributed-feedback lasers, yielding reduced longitudinal spatial hole burning

Jing-Yi Wang, Michael Cada, and Toshihiko Makino

Appl. Phys. Lett. 72, 3255 (1998); http://dx.doi.org/10.1063/1.121615 (3 pages) | Cited 2 times

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An analysis of the nonlinear distributed-feedback (DFB) laser action is presented. A set of nonlinear coupled-power equations is derived. A general condition for a nonlinear DFB laser with reduced spatial hole burning (SHB) is obtained. It is shown that the elimination of SHB in DFB lasers can be achieved by introducing properly-chosen variations of the coupling strength along the longitudinal direction; a novel complex-coupling AR-coated DFB laser diode is proposed as a result. It is also shown that the optical nonlinearity must be considered for the design of high-power laser structures with reduced SHB. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Laser plasma x-ray contact microscopy of living specimens using a chemically amplified epoxy resist

A. C. Cefalas, P. Argitis, Z. Kollia, E. Sarantopoulou, T. W. Ford, A. D. Stead, A. Marranca, C. N. Danson, J. Knott, and D. Neely

Appl. Phys. Lett. 72, 3258 (1998); http://dx.doi.org/10.1063/1.121616 (3 pages) | Cited 7 times

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We report on the use of an epoxy based chemically amplified resist, to produce x-ray images of living biological specimens, exposed with laser plasma generated soft x rays, in the water window (2.3–4.4 nm). The photoresist response was at least two orders of magnitude “faster” than polymethyl methacrylate, the standard resist used so far in soft x-ray contact microscopy. Atomic force and scanning electron microscopy of the biological specimen images, recorded in the resist, clearly showed the flagella of the motile green alga, chlamydomonas, suggesting a lateral resolution better than 150 nm. The resist was also capable of providing height features, as small as 20 nm, in atomic force microscope depth profiles and discriminating the flagella intersection areas. © 1998 American Institute of Physics.
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87.64.kd X-ray and EXAFS
87.80.-y Biophysical techniques (research methods)
07.85.-m X- and γ-ray instruments
87.64.Dz Scanning tunneling and atomic force microscopy
87.17.-d Cell processes

Determination of the optical constants of zinc oxide thin films by spectroscopic ellipsometry

P. L. Washington, H. C. Ong, J. Y. Dai, and R. P. H. Chang

Appl. Phys. Lett. 72, 3261 (1998); http://dx.doi.org/10.1063/1.121617 (3 pages) | Cited 68 times

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Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions, ϵ1(E)+iϵ2(E), of ZnO films on (0001) Al2O3 substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out with E⊥c at angles of incidence of 60° and 65° with respect to the surface normal. Below the band gap, the refractive index n is found to follow the first order Sellmeir dispersion relationship n2(λ) = 1+1.881λ2/(λ2−0.05382). A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.35.-y Excitons and related phenomena

Helicon plasma deposition of a TiO2/SiO2 multilayer optical filter with graded refractive index profiles

Xinrong Wang, Hiroshi Masumoto, Yoshihiro Someno, and Toshio Hirai

Appl. Phys. Lett. 72, 3264 (1998); http://dx.doi.org/10.1063/1.121618 (3 pages) | Cited 21 times

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Thirty one layer TiO2/SiO2 optical filters with graded refractive index profiles were fabricated by helicon plasma sputtering at room temperature. Multilayer films were deposited on glass (BK7) and Si (100) substrates simultaneously and sequentially. The measured transmittance spectrum exhibited a reflectance of 99.8% at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band as a result of the suppression of the sidelobes. The experimental transmittance spectrum corresponded almost completely with that calculated based on the optical multilayer film theory and using the measured refractive indices of TiO2, SiO2 and TiO2–SiO2 composite films. Transmission electron microscopic observations confirmed the expected microstructure of the filter. © 1998 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
81.15.Cd Deposition by sputtering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.79.Ry Gradient-index (GRIN) devices
78.66.Nk Insulators
42.86.+b Optical workshop techniques
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics

Catastrophic optical damage in GaInN multiple quantum wells

Daniel A. Cohen, Tal Margalith, Amber C. Abare, Michael P. Mack, L. A. Coldren, S. P. DenBaars, and David R. Clarke

Appl. Phys. Lett. 72, 3267 (1998); http://dx.doi.org/10.1063/1.121619 (3 pages) | Cited 2 times

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We have observed progressive damage due to reabsorption of stimulated emission in optically pumped laser-quality GaInN–GaN multiple quantum wells. The degradation occurred on a time scale consistent with the lifetime of electrically pumped lasers incorporating the same active region, suggesting that the failure mechanism was in part catastrophic optical damage, and not just heating in the p contact and p cladding as is often assumed. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.45.+h Stimulated emission

Room-temperature ultraviolet laser emission from self-assembled ZnO microcrystallite thin films

Z. K. Tang, G. K. L. Wong, P. Yu, M. Kawasaki, A. Ohtomo, H. Koinuma, and Y. Segawa

Appl. Phys. Lett. 72, 3270 (1998); http://dx.doi.org/10.1063/1.121620 (3 pages) | Cited 723 times

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Room-temperature ultraviolet (UV) laser emission of ZnO microcrystallite thin films is reported. The hexagonal ZnO microcrystallites are grown by laser molecular beam epitaxy. They are self-assembled and parallelly arrayed on sapphire substrates. The facets of the hexagons form natural Fabry–Pérot lasing cavities. The optical gain for the room-temperature UV stimulated emission is of an excitonic nature and has a peak value an order of magnitude larger than that of bulk ZnO crystal. The observation of room-temperature UV lasing from the ordered, nano-sized ZnO crystals represents an important step towards the development of nanometer photoelectronics. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors

Eyesafe pulsed microchip laser using semiconductor saturable absorber mirrors

R. Fluck, R. Häring, R. Paschotta, E. Gini, H. Melchior, and U. Keller

Appl. Phys. Lett. 72, 3273 (1998); http://dx.doi.org/10.1063/1.121621 (3 pages) | Cited 25 times

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We passively Q-switched a diode-pumped Er/Yb:glass microchip laser at a 1.535 μm wavelength using semiconductor saturable absorber mirrors and demonstrated pulses as short as 1.2 ns. By varying the design parameters of the saturable absorber, the pump power, and the pump spot size, we achieved repetition rates from 300 Hz to 100 kHz with pulse energies up to 4 μJ. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Bh Lenses, prisms and mirrors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Spectroscopic light scattering for real-time measurements of thin film and surface evolution

Eric Chason, Michael B. Sinclair, Jerry A. Floro, John A. Hunter, and Robert Q. Hwang

Appl. Phys. Lett. 72, 3276 (1998); http://dx.doi.org/10.1063/1.121622 (3 pages) | Cited 23 times

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We describe a light scattering technique for measuring the real-time evolution of thin film and surface morphology. By using spectroscopic detection, the technique requires no motion of the sample during the measurement, which makes it compatible with many processing geometries. Results from the growth of strained heteroepitaxial layers of SixGe1−x on Si(001) are presented to demonstrate the technique. © 1998 American Institute of Physics.
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78.66.Li Other semiconductors
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Corona discharge: A doping method for polyaniline

Aldo E. Job, José A. Giacometti, and Luiz H. C. Mattoso

Appl. Phys. Lett. 72, 3279 (1998); http://dx.doi.org/10.1063/1.121623 (3 pages) | Cited 3 times

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Corona discharge has been successfully employed to dope thin films of polyaniline coated on poly (ethylene terephthalate) films. Similarly to the conventional doping with aqueous HCl, the process is accompanied by a color change from blue to green and the conductivity can be tuned in the range from 10−10 up to 0.3 S cm−1. This doping method presents several advantages over the conventional one, namely, dry process, use of no chemicals, rapidity and no dopant migration. © 1998 American Institute of Physics.
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82.35.-x Polymers: properties; reactions; polymerization
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
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Large-scale and low-cost synthesis of single-walled carbon nanotubes by the catalytic pyrolysis of hydrocarbons

H. M. Cheng, F. Li, G. Su, H. Y. Pan, L. L. He, X. Sun, and M. S. Dresselhaus

Appl. Phys. Lett. 72, 3282 (1998); http://dx.doi.org/10.1063/1.121624 (3 pages) | Cited 214 times

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Rope-like bundles of single-walled carbon nanotubes (SWNTs) similar to those obtained by laser vaporization and electric-arc techniques were synthesized on a relatively large scale and at low cost by the catalytic decomposition of hydrocarbons at a temperature of about 1200 °C using an improved floating catalyst method. The SWNTs thus obtained have larger diameters and are self-organized into ropes. The addition of thiophene was found to be effective in promoting the growth of SWNTs and in increasing the yield of either SWNTs or multiwalled carbon nanotubes under different growth conditions. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Pyroelectric properties of (Pb1−xLax)TiO3 thin films deposited using SrRuO3 as a buffer layer

Yung-Kuan Tseng, Kuo-Shung Liu, Jian-Der Jiang, and I-Nan Lin

Appl. Phys. Lett. 72, 3285 (1998); http://dx.doi.org/10.1063/1.121625 (3 pages) | Cited 26 times

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In this study, we observed that the ferroelectric properties of (Pb1−xLax)TiO3, (PLT) thin films deposited on Pt/Ti/Si substrates using SrRuO3 as a buffer layer change markedly with the substrate temperature and the composition. All the films are perovskite with no secondary phases when deposited at 500–600 °C. However, only the films deposited below 520 °C possess a satisfactory small leakage current density, for example, JL ⩽ 10−7 A/cm2, under a 50 kV/cm applied field. Both PLT10 (x = 0.10) and PLT5 (x = 0.05) thin films thus obtained possess large pyroelectric coefficient (p = 0.009–0.018 °C−1). However, the PLT10 thin films show pyroelectric properties markedly superior to the PLT5 thin films, although the PLT5 thin films own much better ferroelectric properties. This phenomenon is explained by the lower Curie temperature (Tc) of the PLT10 materials. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.70.+a Pyroelectric and electrocaloric effects
77.80.B- Phase transitions and Curie point

Film thickness and composition monitoring during growth by molecular beam epitaxy using alpha particle energy loss

M. Beaudoin, M. Adamcyk, Z. Gelbart, U. Giesen, I. Kelson, Y. Levy, J. A. MacKenzie, and T. Tiedje

Appl. Phys. Lett. 72, 3288 (1998); http://dx.doi.org/10.1063/1.121626 (3 pages) | Cited 2 times

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The α-particle energy loss method (AEL) has been implemented in situ to monitor film thickness during growth by molecular beam epitaxy. For InP and GaAs substrates recoil implanted with α-particle emitters, we have been able to measure thickness and composition of deposited GaAs, AlGaAs and InGaAs in real time. The AEL method yields in situ real time results comparable in accuracy to those obtained by ex situ scanning electron microscope and high-resolution x-ray diffraction measurements. © 1998 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.80.Jh Ion radiation effects

Metal–oxide bilayer Raman scattering in SrTiO3 thin films

Vladimir I. Merkulov, Jon R. Fox, Hong-Cheng Li, Weidong Si, A. A. Sirenko, and X. X. Xi

Appl. Phys. Lett. 72, 3291 (1998); http://dx.doi.org/10.1063/1.121627 (3 pages) | Cited 18 times

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We have used a metal–oxide bilayer Raman scattering technique to study lattice dynamics in SrTiO3 thin films. The SrTiO3 thin films were epitaxially grown on a conducting metal–oxide layer which reflects the exciting laser beam so that it does not enter the LaAlO3 substrate. Raman scattering from the SrTiO3 thin films was clearly observed, including the first-order Raman peaks forbidden by the cubic symmetry in single crystals. We suggest that strain exists in the films, which changes the crystal symmetry and will affect the dielectric properties of the SrTiO3 thin films. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
78.30.Hv Other nonmetallic inorganics
77.80.-e Ferroelectricity and antiferroelectricity
78.66.Nk Insulators
63.20.-e Phonons in crystal lattices

Crystallization and orientation of C60 from C60/polymethyl methacrylate films

Guanghua Chen and Guobin Ma

Appl. Phys. Lett. 72, 3294 (1998); http://dx.doi.org/10.1063/1.121628 (3 pages) | Cited 1 time

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The crystallization and orientation behaviors of C60 for C60-doped polymethyl methacrylate films are reported. The results show a high tendency of crystallization of C60 with increasing its content, and a preferential (111) orientation for heavily doped films upon high-temperature annealing. The expansion of the lattice constant and the existence of hexagonal close-packed stacking faults are also investigated. The orientation phenomenon indicates an efficient method for the growth of (111)-oriented C60 on a variety of substrates, including those with strong surface bondings on which the orientation is difficult to form via conventional methods.© 1998 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
61.72.Nn Stacking faults and other planar or extended defects

Growth of carbon nanotubes on cobalt disilicide precipitates by chemical vapor deposition

J. M. Mao, L. F. Sun, L. X. Qian, Z. W. Pan, B. H. Chang, W. Y. Zhou, G. Wang, and S. S. Xie

Appl. Phys. Lett. 72, 3297 (1998); http://dx.doi.org/10.1063/1.121629 (3 pages) | Cited 20 times

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We have successfully grown carbon nanotubes on cobalt-implanted silicon with various doses. The morphology of such tubes has been examined by scanning electron microscopy, transmission electron microscopy, and Raman scattering. On contrary to the commonly used transition-metal nanoparticle catalysts, nanometer-sized CoSi2 precipitates produced in the as-implanted substrates are believed to act as nucleation centers for the formation of carbon nanotubes. © 1998 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.30.Hv Other nonmetallic inorganics
78.66.Jg Amorphous semiconductors; glasses

Dynamics of polarization loss in (Pb,La)(Zr,Ti)O3 thin film capacitors

I. G. Jenkins, T. K. Song, S. Madhukar, A. S. Prakash, S. Aggarwal, and R. Ramesh

Appl. Phys. Lett. 72, 3300 (1998); http://dx.doi.org/10.1063/1.121630 (3 pages) | Cited 26 times

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We report results of high-speed polarization relaxation measurements in ferroelectric thin film capacitors. Polarization relaxation has been reported to occur in two distinct time regimes, one for relaxation times in the range of a few milliseconds and a second for longer relaxation times. We find that the polarization relaxation in the first regime is governed by at least two different physical processes, namely depoling fields and the activation field for switching. Using prototypical epitaxial PbZr0.2Ti0.8O3 and Pb0.9La0.1Zr0.2Ti0.8O3 test capacitors, we demonstrate the effect of film microstructure and switching speed on the relaxation dynamics in the first regime. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation
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Visible blind GaN p-i-n photodiodes

D. Walker, A. Saxler, P. Kung, X. Zhang, M. Hamilton, J. Diaz, and M. Razeghi

Appl. Phys. Lett. 72, 3303 (1998); http://dx.doi.org/10.1063/1.121631 (3 pages) | Cited 45 times

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We present the growth and characterization of GaN p-i-n photodiodes with a very high degree of visible blindness. The thin films were grown by low-pressure metalorganic chemical vapor deposition. The room-temperature spectral response shows a high responsivity of 0.15 A/W up until 365 nm, above which the response decreases by six orders of magnitude. Current/voltage measurements supply us with a zero bias resistance of 1011 Ω. Lastly, the temporal response shows a rise and fall time of 2.5 μs measured at zero bias. This response time is limited by the measurement circuit. © 1998 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors

Dominant defect levels in diamond thin films: A photocurrent and electron paramagnetic resonance study

M. Nesládek, L. M. Stals, A. Stesmans, K. Iakoubovskij, G. J Adriaenssens, J. Rosa, and M. Vaněček

Appl. Phys. Lett. 72, 3306 (1998); http://dx.doi.org/10.1063/1.121632 (3 pages) | Cited 32 times

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Characteristic features in photocurrent (PC) and electron paramagnetic resonance (EPR) spectra are discussed and attributed to main defects in the gap of optical-quality chemical vapor deposited diamond. A shoulder in the PC spectra with an onset at about 2.2 eV is attributed to the single-substitutional nitrogen defect (EPR P1 resonance at g = 2.0024). A second feature in the PC spectra with an onset of about 1.3 eV is observed on “as-grown” samples with a hydrogen terminated surface. The defect level associated with this feature is hydrogen related, and this defect disappears after oxidation of the diamond sample surface. The EPR g = 2.0028, which was also suggested to be H-related, is discussed. © 1998 American Institute of Physics.
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71.55.Ht Other nonmetals
73.61.Ng Insulators
76.30.-v Electron paramagnetic resonance and relaxation
73.50.Pz Photoconduction and photovoltaic effects

Suppression of sequential tunneling current by a perpendicular magnetic field in a three-barrier, two-well heterostructure

Yang Ji, Yuanzhen Chen, Kejian Luo, Houzhi Zheng, Yuexia Li, Chengfang Li, Wenchao Cheng, and Fuhua Yang

Appl. Phys. Lett. 72, 3309 (1998); http://dx.doi.org/10.1063/1.121633 (3 pages) | Cited 4 times

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When an intersubband relaxation is involved in vertical transport in a tunneling heterostructure, the magnetic suppression of the intersubband LO or LA phonon scattering may also give rise to a noticeable depression of the resonant tunneling current, unrelated to the Coulomb correlation effect. The slowdown of the intersubband scattering rate makes fewer electrons able to tunnel resonantly between two adjacent quantum wells (QWs) in a three-barrier, two-well heterostructure. The influence of the magnetic field on the intersubband relaxation can be studied in an explicit way by a physical model based on the dynamics of carrier populations in the ground and excited subbands of the incident QW. © 1998 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Strong visible photoluminescence from Ge/porous Si structure

Ting Gao, Song Tong, Xiangqin Zheng, Xinglong Wu, Liming Wang, and Ximao Bao

Appl. Phys. Lett. 72, 3312 (1998); http://dx.doi.org/10.1063/1.121634 (2 pages) | Cited 7 times

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Strong visible photoluminescence was observed on Ge/porous silicon structure prepared by pulsed laser deposition of Ge on porous Si. The photoluminescence spectrum shows three subbands peaked at 400, 620, and 720 nm, respectively. The 400 nm peak was ascribed to GeO color centers, and the 720 nm peak to porous Si. The 620 nm peak is much stronger than the light emitting from the host porous Si. Photoluminescence and transmission electronic microscopy analyses suggest that the strong 620 nm luminescence is the result of the joint function of Ge and porous Si in the transition layer of Ge/porous Si structure. Plausible mechanisms for the 620 nm photoluminescence are discussed. © 1998 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
61.72.J- Point defects and defect clusters

Imaging the depletion zone in a Si lateral pn junction with scanning tunneling microscopy

M. L. Hildner, R. J. Phaneuf, and E. D. Williams

Appl. Phys. Lett. 72, 3314 (1998); http://dx.doi.org/10.1063/1.121635 (3 pages) | Cited 15 times

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Scanning tunneling microscopy (STM) and spectroscopy are used to characterize a lateral pn junction fabricated on a silicon (100) surface. STM images show both an electronic feature and a structural trench at the edges of the ion-implanted p-type regions. The electronic feature widens with applied reverse bias indicating that it is associated with the depletion zone. The electronic feature and its voltage dependence are described qualitatively by modeling the tip-junction system as a series of nonequilibrium metal–insulator–semiconductor diodes formed with a semiconductor of spatially variable carrier density. © 1998 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Cw Elemental semiconductors
61.80.Jh Ion radiation effects
85.40.Ry Impurity doping, diffusion and ion implantation technology
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