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Applied Physics Letters

Issue 21 • Date Nov 1990

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Displaying Results 1 - 25 of 36
  • Amplified spontaneous emission in Tm3+‐doped monomode optical fibers in the visible region

    Page(s): 2169 - 2171
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    We report the observation of amplified spontaneous emission in silica‐based single‐mode optical fibers doped with Tm3+. Frequency upconverted emission was observed in a number of visible and near‐infrared lines after pumping by 1064 nm radiation. The upconversion process is induced via the nonlinear absorption of the infrared beam and enhanced by stimulated Raman scattering in the fiber, leading to amplified spontaneous emission in the blue (∼473 nm) region. View full abstract»

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  • High average power edge emitting laser diode arrays on silicon microchannel coolers

    Page(s): 2172 - 2174
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    We have demonstrated high average power output devices in both one‐dimensional (1‐D) and two‐dimensional (2‐D) arrays of laser diodes using efficient edge emitting cleaved bars and silicon microchannel coolers. These packages are based on the rack and stack architecture. For the 1‐D array a cw optical power output of 22.2 W was obtained with 20% electrical to optical conversion efficiency. For the 2‐D array an average optical power density of greater than 100 W/cm2 was obtained at an efficiency of 25%. View full abstract»

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  • Fission‐fragment‐excited lasing at 585.3 nm in He/Ne/Ar gas mixtures

    Page(s): 2175 - 2177
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    Fission‐fragment‐excited lasing is reported for the 3p’(1/2)0–3s’(1/2)01 neon transition (λ=585.3 nm) in mixtures of He/Ne/Ar. The laser power efficiency peaks at a He/Ne/Ar ratio of approximately 50/2/1 for a laser cell pressure of 1.9 atmospheres. Laser parameters for pump rates from 70 to 1200 W/cm3 are presented for three cavity configurations. View full abstract»

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  • Emission spectroscopy during excimer laser ablation of graphite

    Page(s): 2178 - 2180
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    Emission spectrum of the laser‐induced plasma plume is obtained during KrF excimer laser ablation of graphite in argon and hydrogen gas mixture for deposition of diamond‐like films. Bands of C2 and CN molecules dominate the spectrum while weak CI, CII, and Hα lines are also observed. From the emission intensities, molecular vibrational temperature is calculated to be (12–15)×103 K, and concentrations are estimated to be N(C2)=5×1014 cm-3 and N(CN)=2×1014 cm-3. View full abstract»

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  • Frequency stabilization of an external‐cavity diode laser

    Page(s): 2181 - 2183
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    Using a hybrid optical/electronic technique, an external‐cavity diode laser was frequency stabilized with respect to the sub‐Doppler spectrum of cesium vapor. Laser linewidths of 65 kHz and frequency stabilities of ±10 kHz were obtained. View full abstract»

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  • Effects of strain in multiple quantum well distributed feedback lasers

    Page(s): 2184 - 2186
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    A survey of graded‐index separate confinement multiple quantum well distributed feedback lasers comparing the effects of strain in the quantum well upon threshold, output power, and linewidth is reported. Lasers with either compressive or tensile strained quantum wells and a long cavity length (890 μm) show lower threshold current (10–20 mA) as well as lower linewdith power product than lasers with unstrained quantum wells and have a comparable minimum linewidth to the unstrained quantum well lasers. A minimum linewidth as narrow as 900 and 440 kHz for compressive strain and unstrained quantum well lasers, respectively, was obtained at output power of 30 mW. Single longitudinal mode operation with a maximum output power over 80 mW was observed in all the structures. View full abstract»

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  • Ion beam induced conductivity in chemically vapor deposited diamond films

    Page(s): 2187 - 2189
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    Polycrystalline diamond films deposited by the microwave plasma chemical vapor deposition (CVD) technique onto quartz substrates have been irradiated with 100 keV C and 320 keV Xe ions at room temperature and at 200 °C. The dose dependence of the electrical conductivity measured in situ exhibited complicated, nonmonotonic behavior. High doses were found to induce an increase of up to ten orders of magnitude in the electrical conductivity of the film. The dose dependence of the conductivity for the CVD films was found to be very similar to that measured for natural, type IIa, single‐crystal diamonds irradiated under identical conditions. This result suggests that the conduction mechanism in ion beam irradiated polycrystalline CVD diamond films is not dominated by grain boundaries and graphitic impurities as one might have expected, but rather is determined by the intrinsic properties of diamond itself. View full abstract»

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  • Enhancement of group III atom interdiffusion by nondopant oxygen implants in In0.53Ga0.47As‐In0.52Al0.48As multiquantum wells

    Page(s): 2190 - 2192
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    We show here that the implants of oxygen, a basically nondopant impurity, after adequate high‐temperature annealings (for example, 750 °C, 1 h furnace anneal) lead to a significant interdiffusion of group III atoms in molecular beam epitaxy grown In0.53Ga0.47As‐In0.52Al0.48As multiquantum wells (MQWs). Both photoluminescence and Auger electron spectroscopy measurements (coupled to Ar+ ion etching) have been employed to monitor disordering in MQWs implanted with oxygen (5×1013 to 5×1014 ions cm-2) and subsequently annealed using either rapid thermal anneals or long duration furnace anneals. The role of oxygen to enhance group III atom (Al, Ga, and In) interdiffusion is unambiguously established and a tentative explanation based on a possible migration of oxygen in these MQWs is proposed and dissussed. View full abstract»

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  • Growth of oxide layers on gallium arsenide with a high kinetic energy atomic oxygen beam

    Page(s): 2193 - 2195
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    Oxide layers have been formed on (110) and (100) GaAs wafers by exposure to a high kinetic energy beam of atomic O and characterized using x‐ray photoemission spectroscopy (with Ar+ ion sputter profiling) and Raman spectroscopy. Photoemission shows the reacted layer, ∼500 Å thick, to be uniform in composition and fully oxidized. Raman spectroscopy shows that the substrate is not appreciably disordered during oxidation and in some cases no free‐elemental As is present at the oxide‐substrate interface at a detectable level. View full abstract»

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  • Anomalies of hypersonic velocity and attenuation in vinylidene fluoride‐trifluoroethylene copolymer from Brillouin scattering

    Page(s): 2196 - 2198
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    The hypersonic behavior of a vinylidene fluoride and trifluoroethylene (70/30 mol %) copolymer has been investigated by Brillouin scattering without using index matching liquid. Both the glass and ferroelectric transitions are clearly seen in the acoustic behavior. The home‐prepared sample has excellent optical properties and let us obtain sound attenuation information in the temperature range of 23–123 °C, which another investigator did not discuss because of the bad optical properties of the sample surface. Anomalies of sound attenuation near the transition point have been observed. View full abstract»

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  • Tunneling resonance studies of electronic ministop gap mode in coupled semi‐infinite semiconductor superlattices

    Page(s): 2199 - 2201
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    A numerical technique is developed to analyze the electronic state in coupled semi‐infinite semiconductor superlattices. It is found that the superlattice miniband shrinks to discrete energy levels near the surface, and localized electronic surface states with energy falling within the ministop gap exist under certain conditions. Numerical calculations are also compared with results from an exact eigenvalue equation. View full abstract»

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  • Etching characteristics of Si1-xGex alloy in ammoniac wet cleaning

    Page(s): 2202 - 2204
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    Etching characteristics of Si1-xGex alloys in ammoniac wet cleaning (RCA cleaning) were examined. The etching rate of Si1-xGex became larger with increasing Ge ratio (X). Temperature dependence of the etching rate was studied and the etching rate was large at high temperatures. However, no obvious difference was observed in the temperature dependence of Si1-xGex etching rate at different Ge ratio (X). A surface morhology degradation after RCA cleaning was observed at high Ge ratio (X). A stoichiometry change of Si1-xGex surface after RCA cleaning was observed by x‐ray photoelectron spectroscopy (XPS). The etching rate increase and the surface morphology degradation are thought to be due to the rapid etching of Ge atoms at the top surface layer. View full abstract»

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  • Novel indium oxide/n‐GaAs diodes

    Page(s): 2205 - 2207
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    Diodes with transparent top contacts were fabricated by depositing indium oxide layers onto n‐type GaAs by means of reactive evaporation of In in the presence of oxygen. The electrical characteristics as well as the structural properties and chemical composition of the resulting junctions were studied using Auger electron spectroscopy, x‐ray diffraction, optical absorption, capacitance‐voltage, and dark current‐voltage measurements. The best diodes were obtained under deposition conditions of substrate temperature 250 °C and oxygen pressure 5×10-4 mbar; these diodes exhibited a Schottky barrier height of 0.85 V with an ideality factor of 1.04. The indium oxide films were found to be polycrystalline and to have an electrical resistivity of 3×10-4 Ω cm and an optical transmittance above 90% over the whole visible range. The effect of deviations from the optimal deposition parameters on the diode properties is discussed. View full abstract»

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  • Photoluminescence of quantum well structures with modulated layers grown by an alternating source supply

    Page(s): 2208 - 2210
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    The photoluminescence (PL) spectra from modulated quantum well structures were observed. The modulated quantum well structure comprised a 4 monolayer (ML) modulated layer and an 18 ML GaAs layer between AlAs barrier layers. The modulated layer was grown by incorporating As into a Ga and Al mixture on an AlAs surface. The main peak energy of the PL spectra at 77 K showed a growth temperature dependence; a remarkable red shfit of the main peak energy was observed for samples grown at low temperature. The red shift of the PL peak energy indicates an increase in the effective width of the GaAs well. A rearrangement model of Ga and Al atoms on the AlAs surface during growth with As incorporation into the Ga and Al mixture is proposed to explain the growth temperature dependence of the PL peak energy. View full abstract»

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  • Si‐H and N‐H vibrational properties in glow‐discharge amorphous SiNx:H films (0≪x≪1.55)

    Page(s): 2211 - 2213
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    Amorphous SiNx:H films were prepared by rf glow discharge of SiH4‐NH3 mixtures at 300 °C, and the SiH, NH, and SiN vibrational absorptions were investigated as a function of x. The stretching absorption profiles due to SiH and SiN bonds are reproduced by a superposition of two components at around 2000 and 2100 cm-1, and of three components at around 750, 840, and 960 cm-1, respectively. The dependence of these intensities on x was examined by means of a generation probability analysis on the basis of the random bonding model including SiH and NH bonds which play an important role in the film growth mechanism. View full abstract»

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  • Defects in preamorphized single‐crystal silicon

    Page(s): 2214 - 2216
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    Direct electrical characterization of 1‐μm‐thick Si+ preamorphized and epitaxially regrown silicon layers has revealed a low concentration of residual deep‐level defects within the regrown layer. A deep‐level trap at Ec -0.40 eV has been found associated with the amorphous‐crystalline boundary dislocation loops. In addition, a near mid‐gap trap at Ev+0.54 eV, observed in p‐type samples, is believed to be responsible for a spatially localized generation current of ∼2×10-6 A/cm2 associated with the dislocation loops. View full abstract»

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  • Characterization of rapid thermally nitrided SiO2/Si interface by the conductance technique

    Page(s): 2217 - 2219
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    Device quality SiO2 films with a thickness of 15 nm have been thermally nitrided in NH3 by a rapid thermal processing technique. The properties of the interface between these films and a Si substrate have been investigated by a conductance technique. The results show that the nitridation increases the density and time constant of interface states and enhances the fluctuation of surface potential, but changes the hole capture cross section only slightly. Specifically, nitridation introduces a peak of interface states at 0.25 eV below midgap and the energy dependency of hole capture cross section is suppressed. Using a patchwork model, the surface potential fluctuation can be well simulated and a surface charge nonuniformity with a long‐wavelength distribution may exist. These are consistent with the fact that nitridation induces a high oxide charge density. Experimental data show that all these properties depend on nitridation time and temperature. View full abstract»

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  • Observation of Lomer–Cottrell locks in SiGe strained layers

    Page(s): 2220 - 2221
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    Misfit dislocations in the SiGe system are usually not dissociated. We present the first observation of a Lomer–Cottrell lock array in a Si/Si1-xGex/Si heterostructure (0.4≪x≪0.6). We describe the character of the stacking faults and the partial dislocations which form the locks. View full abstract»

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  • Excimer‐laser‐induced crystallization of hydrogenated amorphous silicon

    Page(s): 2222 - 2224
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    The electronic transport properties and structural morphology of fast‐pulse excimer‐laser‐ crystallized hydrogenated amorphous silicon (a‐Si:H) thin films have been measured. The room‐temperature dark dc conductivities and Hall mobilities increase by several orders of magnitude at well‐defined laser energy density thresholds which decrease as the impurity concentration in the films increases. The structural morphology of the films suggests an impurity‐induced reduction of the a‐Si:H melt temperature as the origin of this behavior. View full abstract»

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  • Multicomponent structure in the temperature‐dependent persistent photoconductivity due to different DX centers in AlxGa1-xAs:Si

    Page(s): 2225 - 2227
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    The persistent photoconductivity of Si‐doped AlGaAs has been investigated by temperature‐dependent resistance and Hall effect measurements. After illuminating the samples at low temperature, we observe for the first time distinct structures in the temperature‐dependent carrier concentration during the subsequent heating process. These structures are interpreted in terms of the existence of different DX levels below the conduction‐band edge. View full abstract»

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  • Molecular beam epitaxial growth of high quality GaAs on untilted (001) Si substrates assisted by electron beam irradiation

    Page(s): 2228 - 2230
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    Using molecular beam epitaxy assisted by an electron beam irradiation with a beam energy of 50 keV at an angle of incidence 5°, we have successfully grown high quality GaAs layers on untilted (001)Si substrates. Raman spectra show that this technique reduces crystalline imperfections usually found in GaAs layers grown (001)Si substrates by a factor of 20, clearly demonstrating the effectiveness of this technique. Typical low‐temperature photoluminescence spectra of undoped GaAs on Si contain four features at emission energies of 1.503, 1.488, 1.471, and 1.434 eV. The full width at half maximum (FWHM) of the bound excitonic peak with heavy holes is 2.8 meV, which can be one of the narrowest ever reported. The incident electron beam is expected to play several roles, such as cleaning Si surfaces by removing carbon/oxygen residuals, enhancement of migration rates of adatoms on the growing surface, and acceleration of the single‐domain formation during the growth. View full abstract»

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  • Novel electron interferometers using field‐induced decoupling in double quantum well structures

    Page(s): 2231 - 2233
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    Novel Aharonov–Bohm type electron interferometers are proposed, which have no curved electron waveguide structures to form a ring geometry. But instead the ring geometry is effectively constructed in a straight double quantum well structure, by the control of the shapes of the wave functions by electric fields. The interferometer has a perfect single‐mode channel in each arm of the interferometer as well as the exact 1:1 branching ratio to the two arms, for each electron moving in the plane of the ring. View full abstract»

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  • Electro‐optical bistability in strained InxGa1-xAs/Al0.15Ga0.85As multiple quantum wells

    Page(s): 2234 - 2236
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    Using photocurrent spectroscopy, we have studied optical absorption properties of strained InxGa1-xAs/Al0.15Ga0.85As multiple quantum wells grown by molecular beam epitaxy in the presence of electric fields perpendicular to the heterointerface. In the wavelength region where the bulk GaAs substrate is transparent, we observe the quantum confined Stark effect. Optical bistability of a self‐electro‐optic effect device is demonstrated at room temperature without removal of the GaAs substrate. View full abstract»

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  • Conservation and filling of neutral hole traps in SiO2 during ionizing radiation exposure

    Page(s): 2237 - 2238
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    The question of whether ionizing radiation creates fixed positive charge and/or neutral hole traps, or simply fills existing neutral hole traps has been examined by equating the density of intrinsic neutral hole traps, present before irradiation, with the sum of fixed positive charge and the remaining neutral hole traps present after x‐ray irradiation. The total number of positive Coulombic and neutral hole traps was found to remain constant, regardless of the level of radiation the device receives. This indicates strongly that fixed positive charge represents filled intrinsic hole traps and that additional hole trapping defects, except for a small amount of fixed negative charge, are not generated by ionizing radiation in the photon energy range studied. View full abstract»

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  • Epitaxy of (100) Cu on (100) Si by evaporation near room temperatures: In‐plane epitaxial relation and channeling analysis

    Page(s): 2239 - 2240
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    The epitaxial growth of (100) Cu on (100) Si reported recently using evaporation is analyzed to determine the epitaxial relation between Cu and Si, and also the crystalline quality of the Cu films. A 45° rotation between the (100) plane of Cu and that of Si around their (001) axis is shown to be needed for the lattice match. Such an epitaxial relation is confirmed by the grazing angle x‐ray diffraction, with the [010] of Cu parallel to the [011] of Si. The channeling analysis of a 2‐μm‐thick Cu film shows a 10% minimum near the surface. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory