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Applied Physics Letters

Issue 3 • Date Jan 1993

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Displaying Results 1 - 25 of 41
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Direct photoetching of polymer films using vacuum ultraviolet radiation generated by high‐order anti‐Stokes Raman scattering

    Page(s): 211 - 213
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    High‐order anti‐Stokes Raman pulses of the vacuum ultraviolet were successfully utilized for ablation of polymer films. Efficient anti‐Stokes conversion of the fourth harmonics of a conventional Nd:YAG laser provided fluences as large as 0.4 J/cm2 for a sixth‐order anti‐Stokes pulse at 160 nm. The selection of irradiation wavelength by a ready choice of scattered orders of Raman waves could verify critical wavelength dependence of ablation effect, which turned out that only the light at 160 nm made it possible to ablate polytetrafluoroethylene (PTFE) film with such low fluences. View full abstract»

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  • Photoconduction in germanium and phosphorus doped silica waveguides

    Page(s): 214 - 216
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    Photoconduction measurements on Ge‐P doped silica planar ridge waveguides exposed to several miliwatts of ultraviolet radiation are reported. It is shown that there is a strong reduction in the photocurrent with time of exposure pointing to a depletion in the available photoactivated carriers. The density of defects is directly inferred from the measurements. View full abstract»

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  • Use of the Talbot effect to couple the phases of lasers

    Page(s): 217 - 218
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    Antyukhov et al. [JETP Lett. 44, 78 (1986)] first proposed that a normal and partly reflecting mirror be placed a distance a2/λ in front of a laser array to synchronize and phase lock them. Then the Talbot effect, said to produce source ‘‘self‐imaging,’’ forms an ‘‘array image’’ on the array. However, a basic relation of Fresnel diffraction is now found to indicate that the method as used is inherently flawed. The Talbot effect actually introduces phase shifts into some of the reflected light which make the total output nonuniform in phase. This produces a complex amplitude pattern in Talbot planes different from the grating output. Then the various lasers will not emit in phase. View full abstract»

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  • Frequency tuning of a double‐heterojunction AlGaAs/GaAs‐vertical‐cavity surface‐emitting laser by a serial integrated in‐cavity modulator diode

    Page(s): 219 - 221
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    The frequency tuning of a vertical‐cavity surface‐emitting laser through current injection is reported herein. This was achieved by integrating an AlGaAs graded‐index p–n‐modulator diode with a double‐hetero GaAs/AlGaAs laser diode in a vertical cavity formed by an AlAs/AlGaAs‐Bragg reflector and a metallic mirror. Experimental results show an obtained gradient of frequency shift up to 0.93 GHz/mA by the modulator current. This effect is at present restricted to approximately 40 mA due to thermal effects. A theoretical model based on the plasma effect and thermal effects agrees with the experimental values and predicts a maximum value for the gradient of frequency shift of 1.15 GHz/mA with the presented structure.   View full abstract»

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  • Fused silica masks for printing uniform and phase adjusted gratings for distributed feedback lasers

    Page(s): 222 - 224
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    A method for producing durable fused silica self‐interference grating photomasks is described. These masks allow repeated printing of both uniform and phase adjusted gratings. Periods as fine as 200 nm have been demonstrated. The fabrication of these masks via holographic and focused ion beam lithography and their use as a lithography tool are explained. Distributed feedback lasers, with gratings made by this technique, were produced. These lasers operated in a single longitudinal mode at a wavelength of either 1.55 or 1.3 μm. View full abstract»

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  • Biexciton lasing in CuCl quantum dots

    Page(s): 225 - 227
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    Lasing of CuCl microcrystals embedded in a NaCl single crystal was observed for the first time. The lasing takes place at 77 K in a sample sandwiched between dielectric mirrors under pulsed ultraviolet laser excitation. The lasing transition is that from biexciton to exciton. The lasing is observed up to 108 K. The optical gain of the sample is almost the same as that of a CuCl bulk crystal in spite of the low concentration of CuCl in the NaCl matrix. View full abstract»

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  • Influence of ion energy on the physical properties of plasma deposited SiO2 reset films

    Page(s): 228 - 230
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    Silicon dioxide films have been deposited using a SiH4+O2 microwave plasma excited by distributed electron cyclotron resonance. The ratio of flow rates of the reactive gas was O2/SiH4∼7. The substrate was not heated intentionally (T≪150 °C). The effect of ion energy during deposition, in the 10–150 eV range, has been studied through refractive index, infrared absorption bands, chemical etch rate, and electrical measurements. For ion energies ≳50 eV, many of the film characteristics are close to those of thermal SiO2 View full abstract»

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  • Effect of powder synthesis procedure on calcium site occupancies in barium calcium titanate: A Rietveld analysis

    Page(s): 231 - 233
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    (Ba,Ca)TiO3 samples with the ratio of (Ba+Ca) to Ti as unity but prepared by (i) a semiwet route involving (Ba,Ca)CO3 solid solution precursors and TiO2 and (ii) the conventional dry route involving BaCO3, CaCO3, and TiO2 powders, exhibit diffuse and BaTiO3‐type sharp ferroelectric phase transitions, respectively. Rietveld analysis of neutron powder diffraction data from the two types of samples shows that, whereas in the samples prepared by the semiwet route, Ca2+ exclusively occupies the Ba2+ site, nearly half of the substituted Ca2+ occupies the Ti4+ site in the case of samples prepared by the dry route. We show that Ca replacement at the Ba site leads to diffuseness whereas Ca introduction at the Ti site leads to sharpening of the transition. To our knowledge, this is the first clear demonstration of the powder synthesis procedure affecting the substitutional sites in multicomponent ceramics and this, in turn, influencing their physical behavior drastically. View full abstract»

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  • Oxygen desorption from molybdenum oxide by synchrotron radiation and its surface‐cleaning applications

    Page(s): 234 - 236
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    The effects of synchrotron radiation (SR) irradiation on molybdenum oxide are studied. Removal of native molybdenum oxide by SR irradiation is observed by reflection high‐energy electron diffraction and Auger‐electron spectroscopy measurements. SR irradiation changes MoO3 thin films to MoO2. Indications are that SR‐stimulated oxygen desorption is the cause. Those SR‐irradiated molybdenum surfaces which are originally covered with native oxide are found to be highly reactive with disilane gas, while nonirradiated surfaces are not. View full abstract»

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  • keV ion sputtering of hydroxyapatite

    Page(s): 237 - 239
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    Thin films of hydroxyapatite have been deposited by 5 keV ion sputtering on titanium substrates at room temperature. The sputtering yield is about 5×10-2 molecules/ion for argon beam and shows a linear trend with the ion nuclear stopping power of incoming beams. Noble gases have been adopted to avoid chemical reaction between implanted ions and hydroxyapatite target. Auger electron spectroscopy has been used in a high vacuum chamber to measure in situ the stoichiometry of the deposited film. View full abstract»

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  • Metalorganic chemical vapor deposition of TiN films for advanced metallization

    Page(s): 240 - 242
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    Titanium nitride (TiN) films are used extensively in advanced metallization schemes for ultralarge scale integrated applications. In the present experiments, physical properties of thin TiN films deposited using low pressure chemical vapor deposition from tetrakis‐dimethyl‐amino titanium and ammonia have been investigated. Deposited films were characterized by resistivity, stoichiometry and etch rates. It was found that bulk resistivity correlated to wet etch rates with high resistivity films having higher wet etch rates. High bulk resistivity films were unstable in atmosphere and Auger analysis showed higher relative oxygen content. It is concluded that high resistivity films are low density and thereby susceptible to ex situ contamination. Optimized films had bulk resistivity of 250 μΩ cm and wet etch rates comparable to reactively sputtered TiN.   View full abstract»

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  • Formation of epitaxial CoSi2 on Si(100): Role of the annealing ambient

    Page(s): 243 - 245
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    With a thin Ti layer interposed between a Si(100) substrate and a Co overlayer, the inversion of the Co and Ti films and the formation of a partly relaxed epitaxial CoSi2 layer on Si(100) can be obtained by steady‐state annealing in inert as well as reactive ambients. A reactive ambient chemically binds the Ti near the surface as an oxide or nitride layer, which preserves the bilayer structure during a high temperature treatment. In a nonreactive ambient, the Ti and CoSi2 layers react further, resulting in a uniform layer of Co0.25Ti0.75Si2 and CoSi2. An eptiaxial orientation of CoSi2 is retained even in that case. View full abstract»

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  • Determination of the residual stress tensor in Cu/W multilayers by x‐ray diffraction

    Page(s): 246 - 248
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    A direct determination of the residual stress tensor in Cu/W multilayers has been performed by x‐ray diffraction using the ‘‘sin2 ψ’’ method. In tungsten sublayers, we found a compressive and isotropic stress in the plane parallel to the multilayer surface of a very high value equal to -6.4 GPa. Furthermore, using stress‐strain relations, the tungsten lattice structure resulting from strains is calculated: the strained W bcc structure is found to be similar to a monoclinic‐like structure leading to important modifications of the diffraction pattern. View full abstract»

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  • Femtosecond thermomodulation measurements of Co/Cu and Ag/Cu multilayer films

    Page(s): 249 - 251
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    Femtosecond transient reflectivities of Co/Cu and Ag/Cu multilayer films were measured to study the electron‐lattice relaxation in these systems. The measurement results suggest that the thickness of Cu layers does not influence the electron relaxation time. A slow decaying signal, which is absent in Ag/Cu films, was observed in Co/Cu films and it is attributed to the spin excitations in the Co layers. View full abstract»

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  • Carrier profile evaluation for a Zn‐doped InGaAsP/InGaAsP multiquantum well using a low‐temperature capacitance‐voltage method

    Page(s): 252 - 254
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    We studied the carrier profile of a Zn‐doped InGaAsP/InGaAsP multiquantum well (MQW) using capacitance‐voltage (C‐V) measurement. Lowering the temperature to 77 K suppresses the Debye length, allowing us to obtain a detailed carrier profile. Furthermore, we propose a method for analyzing the carrier profile, taking the exact depletion layer extension at pn junction into account. Applying the analysis, we obtained the actual carrier profile in the doped MQW with agreement between the peak position in the profile and the well position of MQW. This shows that the low‐temperature C‐V measurement is effective for investigating the carrier profile in MQW. View full abstract»

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  • Integration of low‐temperature GaAs on Si substrates

    Page(s): 255 - 257
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    GaAs was grown on Si substrates by molecular‐beam epitaxy at low substrate temperatures. Femtosecond time‐resolved reflectivity investigations revealed a significant reduction of carrier lifetime in GaAs epilayers from 14 ps to ≪0.5 ps as the growth temperature was reduced from 400 to 150 °C. Photoconductors were fabricated on the epilayers, and electro‐optic sampling was used to confirm the electrical response times of ≪1 ps. The responsivity is comparable to that for low‐substrate‐temperature GaAs grown on GaAs substrates, with a photogenerated carrier mobility of ∼100–300 cm2/V s. The low growth temperatures allow ultrafast GaAs‐based photodetector incorporation into Si‐based integrated circuits for novel optoelectronic applications. View full abstract»

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  • Mg doping of InP and InGaAs grown by metalorganic molecular beam epitaxy using bis‐cyclopentadienyl magnesium

    Page(s): 258 - 260
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    We have investigated the feasibility of Mg doping using bis‐cyclopentadienyl magnesium (Cp2Mg) during growth of InP and InGaAs by metalorganic molecular beam epitaxy. In InP, hole concentrations between 5×1016 and 4×1018 cm-3 were readily attained without degradation of the surface morphology. Comparison with secondary ion mass spectrometry analysis shows good electrical activation for concentrations ≤2×1018 cm-3 though compensation at low doping levels was observed due to compensation from carbon and oxygen impurities which were present at levels of 9×1016 and 5×1016 cm-3, respectively. Mg profiles in InGaAs tended to be more abrupt than those in InP and hole concentrations up to 1019 cm-3 were achieved. p‐InGaAs/n‐InP structures annealed at 600 °C for 10 s showed no evidence of Mg diffusion. View full abstract»

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  • Band offset variations at Ge/GaAs (100) interfaces

    Page(s): 261 - 263
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    We analyze the band offsets at Ge/GaAs (100) interfaces by internal photoemission, capacitance/voltage and current/voltage measurements. The conduction band offset varies with Ge growth temperature from -0.025 eV for 300 °C to 0.33 eV for 500 °C. We attribute these drastic offset variations to different microscopic interface configurations at the polar Ge/GaAs (100) heterojunction. View full abstract»

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  • Quantum pillar structures on n+ gallium arsenide fabricated using ‘‘natural’’ lithography

    Page(s): 264 - 266
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    Random arrays of CsCl hemispherically shaped islands with average diameters as small as 500 Å have been made on n+GaAs substrates. The CsCl behaves as a resist of high selectivity when the GaAs is reactively ion etched in a BCl3 plasma. The resulting structure is a set of pillars all the same height, but with varying diameters, typically ±15% of the average value, 〈D〉. Typical pillar packing density, S, is 20%. Photoluminescence (PL) studies were made at 10 K on n+ and semi‐insulating GaAs using 514.5 nm exciting radiation. PL spectra from n+GaAs structures of 〈D〉=520±78 Å, h=800 Å, S=20%; 〈D〉=610±97 Å, h=450 Å, S=12%; 〈D〉=1215±210 Å, h=600 Å, S=20%, as well as a plane surface, are reported. There is a shift in the peak value of the PL curves with respect to the planar structure of 26, 13, and 2.5 meV, respectively. It may be possible to understand these shifts in terms of quantum confinement effects if the effective pillar size is reduced by surface space charge effects. View full abstract»

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  • Acoustic phonon peak splitting and satellite lines in Raman spectra of semiconductor superlattices

    Page(s): 267 - 269
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    Folded longitudinal acoustic phonon peak splitting and sets of satellite lines are observed in high resolution Raman spectra of Si/Si1-xGex superlattices. Analysis shows that the phonon peak splittings are possibly due to a variation in the superlattice periodicity and the sets of satellite lines originate from the interference of the folded longitudinal acoustic phonons and the confined acoustic phonons in the superlattice film. These fine structures in Raman spectra enable a detailed characterization of the superlattices. View full abstract»

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  • Novel technique for p‐type nitrogen doped ZnSe epitaxial layers

    Page(s): 270 - 272
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    We report a novel technique to obtain p‐type ZnSe layers doped with nitrogen. The layers were grown in a low‐pressure metalorganic vapor phase epitaxy system using ammonia as the dopant source. A rapid thermal anneal was used to enhance the activation of the nitrogen acceptors. Net acceptor concentration values as high as 3×1016/cm3 were obtained from capacitance‐voltage measurements and the profile was uniform over the thickness of the epitaxial layers. The 7 K photoluminescence spectrum was dominated by the acceptor bound exciton peak; the donor‐acceptor pair spectra were also observed. View full abstract»

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  • Shallow donor in separation by implantation of oxygen structures revealed by electric‐field modulated electron spin resonance

    Page(s): 273 - 275
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    Electric‐field modulated K‐band electron spin resonance measurements on Si/SiO2/Si structures, formed by implantation of oxygen (SIMOX), were carried out at 4.3–30 K. Large area metal‐oxide‐silicon capacitors were fabricated on these structures and optimized for cavity loading. Sweeping of the Si band gap through the Fermi level near the buried oxide interfaces resulted in the observation of a shallow donor in Si of fairly high local density (≊1018 cm-3), residing in this area; its electron spin resonance signal is turned on and off by positive and negative gate biasing, respectively. The same donor signal has previously been observed in γ‐irradiated SIMOX, revealing that γ irradiation has the same effect as positive biasing. View full abstract»

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  • Iron‐induced alternating current surface photovoltages in n‐type silicon wafers

    Page(s): 276 - 277
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    Alternating current surface photovoltage (SPV) is observed in n‐type silicon wafers, which are treated with an iron (Fe)‐contaminated alkaline solution composed of ammonia hydroxide, hydrogen peroxide, and water, indicating that the negative charge appears at wafer surfaces. With the removal of the native oxide, where the residual concentration of Fe is 4.6×1016 atoms/m2, Fe concentration is reduced to the detection limit (4.4×1013 atoms/m2) at the wafer surface, and then the ac SPV vanishes. This result provides evidence that Fe in the native oxide contributes to the negative charge induction, similar to results previously reported for aluminum. View full abstract»

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  • On the estimation of depth resolution during sputter profiling

    Page(s): 278 - 280
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    We have estimated broadening of sputter profiles for several elements, either buried or implanted in Si, under Ar+, Cs+, and O2+ bombardment using a semiempirical model developed recently by P. C. Zalm and C. J. Vriezema [Nucl. Instrum. Methods B 67, 495 (1992)]. Excellent agreement has been found between this model and experimental data for all three types of primary ions. In the case of oxygen bombardment, however, good agreement is only achieved by taking into account beam‐induced changes at the surface, including swelling and the formation of a surface oxide. 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