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Applied Physics Letters

Issue 18 • Date Nov 1986

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Displaying Results 1 - 25 of 30
  • Continuous control of coherence length in separately pumped (AlGa)As lasers

    Page(s): 1129 - 1131
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    Continuous control of coherence length is realized in the output power region of 3–5 mW by changing the current flowing into the loss region of separately pumped (AlGa)As lasers. The controllable saturable absorption makes lasing spectra multimode and broadens the linewidth of an individual laser mode up to 2.5 Å through self‐pulsation. The threshold current of the laser is 60–80 mA. The lasing wavelength is around 780 nm. View full abstract»

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  • Laser beam modulator and pulse former with an adjustable transmission‐voltage characteristic provided by persistent spectral hole burning

    Page(s): 1132 - 1134
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    The transmission of a polymer film doped with dye molecules is modulated by voltage‐induced changes of the population in the center of a persistent spectral hole. It is demonstrated that the transmission versus voltage characteristic of the sample is adjustable to the requirements of the desired application by applying a selected time‐dependent voltage during spectral hole burning. Various characteristic curves have been tailor made and used for modulation and pulse forming of laser beams. View full abstract»

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  • Observation of gain compression in a GaAlAs diode laser through a picosecond transmission measurement

    Page(s): 1135 - 1137
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    The carrier density and light output of a pulse modulated GaAlAs diode laser were measured with picosecond time resolution. A new technique for measuring carrier density by transmission of picosecond light pulses through a diode laser is described. The measured carrier density was compared with a density calculated from the light output data using a rate equation analysis. Gain compression of a magnitude expected from relaxation oscillation damping rates was observed. Because the experiment measures the density at the center of the waveguide, and not the average across the active layer, the compression mechanism is not spatial hole burning. View full abstract»

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  • Surface‐emitting GaAlAs/GaAs linear laser arrays with etched mirrors

    Page(s): 1138 - 1139
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    Surface‐emitting GaAlAs/GaAs linear laser arrays are fabricated using the ion milling technique. Low threshold current and differential quantum efficiency comparable to these of the cleaved device are obtained. View full abstract»

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  • Hologram fixing process at room temperature in photorefractive Bi12SiO20 crystals

    Page(s): 1140 - 1142
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    We present the first demonstration of a room‐temperature grating fixing process in a photorefractive Bi12SiO20 crystal. This arises from a space‐charge compensation due to a hole conduction when the crystal is placed in the dark for 1–3 min. The grating is optically revealed by redistribution of photoelectrons through the uniform illumination of the crystal. After compensation and optical revelation, the readout time constant of the grating is increased by a factor of 40×. Electrical revelation of fixed gratings and holographic images is also demonstrated. View full abstract»

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  • New singlet oxygen generator for chemical oxygen‐iodine lasers

    Page(s): 1143 - 1144
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    Experiments have been carried out to investigate a new method for generating O2(1Δ) with long‐time operation of an efficient chemical oxygen‐iodine laser system in mind. An impinging‐jet nozzle was utilized to atomize a H2O2‐KOH solution so that the alkaline H2O2/Cl2 reaction might occur in droplet‐gas phase with high excitation efficiency. Experimental results indicate that the present generator can yield as high as 80% of O2(1Δ) with reasonable O2 flow rate. View full abstract»

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  • Low threshold operation of a GaAlAs/GaAs distributed feedback laser with double channel planar buried heterostructure

    Page(s): 1145 - 1147
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    We describe a GaAlAs/GaAs distributed feedback (DFB) laser with double channel planar buried heterostructure operating at λ=0.88 μm. The device has been prepared using three‐step liquid phase epitaxy. A cw threshold current as low as 12 mA at room temperature has been accomplished even with third‐order diffraction gratings. A single longitudinal mode oscillation without mode hopping has been observed at any injection level over a temperature range of 60 K. These characteristics are indeed almost comparable to the well‐developed quaternary counterparts, thus showing that the excellent spectral purity of DFB lasers will soon be available in the fields where shorter wavelengths are needed. View full abstract»

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  • V‐groove distributed feedback laser for 1.3–1.55 μm operation

    Page(s): 1148 - 1150
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    We describe a V‐groove distributed feedback laser operating at λ=1.5 μm. A second‐order diffraction grating has been defined by electron beam writing and transferred using ion beam milling after the crystal growth was completed. A single longitudinal mode operation with a mode rejection ratio larger than 5000:1 has been obtained under modulation rate of 1 GHz. The techniques used in this work can be applied to other types of buried heterostructure lasers. View full abstract»

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  • Attenuation of far‐infrared surface plasmons on overcoated metal

    Page(s): 1151 - 1153
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    The attenuation of far‐infrared (λ=0.119 mm) surface plasmons has been measured as a function of the thickness of a silicon overlayer on top of silver. Good agreement with theory was obtained indicating that the Drüde model for the dielectric constant of silver is valid out to these wavelengths. View full abstract»

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  • Induced resonance electron cyclotron quasi‐optical maser in an open resonator

    Page(s): 1154 - 1156
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    In this letter we analyze an induced resonance electron cyclotron (IREC) quasi‐optical maser configuration, which has the unique features of being highly efficient and, with the proper choice for the index of refraction, relatively insensitive to the electron beam’s energy spread. The radiation mechanism can, however, be sensitive to the beam’s pitch angle spread. A system of nonlinear coupled orbit equations, describing the dynamics of electrons in a spatially varying magnetic field, and the electromagnetic field of a steady‐state open resonator configuration are derived and analyzed. Furthermore, we show that by appropriately tapering the magnetic field an induced resonance condition can be achieved which results in high interaction efficiencies. It is anticipated that an efficient, high power millimeter, submillimeter, and infrared radiation source can be realized with the IREC quasi‐optical maser configuration. View full abstract»

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  • Ion beam induced conductivity and structural changes in diamondlike carbon coatings

    Page(s): 1157 - 1159
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    Energetic ion beam irradiation of diamondlike carbon thin films induces a decrease of 4–5 orders of magnitude in the resistivity of the films from their as‐grown value of 107 Ω cm. The initial decrease in resistivity with increasing ion dose is due to the loss of hydrogen from the films with a concomitant decrease in the optical band gap. Heating the films during the irradiation greatly accelerates the rate of hydrogen loss as a function of dose. Once the hydrogen removal is complete, further irradiation increases the film conductivity by inducing the growth of microcrystallites of graphite. View full abstract»

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  • Time‐resolved reflectivity measurements during explosive crystallization of amorphous silicon

    Page(s): 1160 - 1162
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    Explosive crystallization of Cu implanted amorphous silicon during irradiation by a 32‐ns FWHM ruby laser pulse has been studied using time‐resolved reflectivity measurements and Rutherford backscattering spectrometry. From interferences in the reflectivity, the position and the velocity of the self‐propagating melt have been deduced as a function of time. A maximum average velocity of 13±2 m/s has been obtained. The reflectivity behavior indicates the presence of crystalline nuclei in the melt. View full abstract»

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  • Glass forming ability in mechanically alloyed Fe‐Zr

    Page(s): 1163 - 1165
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    Amorphous Fe‐Zr powders have been prepared by mechanical alloying in a powder mill. The samples are characterized by x‐ray diffraction, differential scanning calorimetry, and saturation magnetization measurements. The glass forming range reaches from 30 to 78 at. % Fe being much wider than for melt‐spun samples. Eutectic concentrations do not play any role. The results are compared with the glass forming ability predicted by free‐enthalpy diagram calculations based on the Miedema model [A. R. Miedema, Philips Tech. Rev. 36, 217 (1976)]. Amorphization by mechanical alloying seems to be a metastable equilibrium process neglecting intermetallic phases. Rather high crystallization temperatures are found in the concentration range which is not accessible by melt spinning. View full abstract»

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  • Atomic point‐contact imaging

    Page(s): 1166 - 1168
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    In tunneling microscopy a potential barrier separates a pointed tip from the sample to be investigated. In this letter we show that atomic resolution can be achieved in special cases where the gap spacing has been reduced to the point where the potential barrier may have completely collapsed. In this example the tip may be said to be touching the sample. The forces between the tip and sample are then strongly repulsive and the possibility exists for studying tribology on an atomic scale. View full abstract»

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  • Transmission electron microscopy of aluminum implanted and annealed (100) Si: Direct evidence of aluminum precipitate formation

    Page(s): 1169 - 1171
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    Aluminum implantation into (100) Si has been studied here by transmission electron microscopy (TEM), secondary ion mass spectrometry, and spreading resistance methods. For the implantation conditions (2×1015 cm-2, 200 keV, room temperature) used in our experiments a buried amorphous layer is created from 50 to 300 nm below the surface. During N2 annealing at 600–1000 °C, two discrete layers of dislocations at (110 and 330 nm) bounding a band of precipitates (≫1011 cm-2) were created, accompanied by a pronounced redistribution of Al in the implanted region. Three Al peaks at depths corresponding to the defect layers observed by TEM appeared. The positions and number of the peaks remained almost unaffected as a function of annealing temperature. High resolution TEM showed that the band of precipitate contained oriented Al particles and that these particles also nucleated on dislocations. The stability of the Al peak and associated low electrical activity (≪10%) has been explained by taking into account the formation of Al precipitates and their interaction with the oxygen in the surrounding regions. View full abstract»

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  • Tunneling microscopy in an electrochemical cell: Images of Ag plating

    Page(s): 1172 - 1174
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    A scanning tunneling microscope (STM) operating in an electrochemical cell was used to observe Ag films that had been electrodeposited on a graphite substrate. Before Ag deposition and after stripping the deposited Ag, the atomic features of the graphite substrate were observed. The observed STM images are consistent with an island film growth mechanism. This initial study demonstrates that STM studies of electrochemical processes occurring at electrodes in solution are now possible. View full abstract»

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  • Mass spectroscopic identification of wavelength dependent UV laser photoablation fragments from polymethylmethacrylate

    Page(s): 1175 - 1177
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    Samples of polymethylmethacrylate have been irradiated with laser pulses of 266 nm wavelength along with the wavelengths generated via hydrogen‐shifted stimulated Raman scattering. A quadrupole mass spectrometer monitors in real time the photoablation products produced during the irradiation. At wavelengths of 266 nm and above, the products are dominated by monomer, CO2, and CO. At wavelengths below 266 nm, a dramatic change of ablation products is observed, with methyl formate appearing as a major photochemical product. View full abstract»

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  • Wide‐gap boron‐doped microcrystalline silicon nitride

    Page(s): 1178 - 1180
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    Microcrystalline SiNx:H films were prepared by rf glow discharge of SiH4‐B2H6‐N2‐H2 mixtures with the gas volume ratio of B2H6/SiH4=4.5×10-3. The volume fraction of the crystalline phase and the crystallite size decrease with an increase in N content x, and the films were amorphous at x above 0.2. The dark conductivity σd decreases and the optical gap Eg increases with x. The gap‐state density is lowest at x near 0.2, where σd∼10-2–10-3/Ω cm (the activation energy is 0.1 eV) and Eg∼1.9 eV. These electrical properties are improved as compared with those for B‐doped amorphous SiNx:H. View full abstract»

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  • Photoluminescence study of the shallow donor neutralization in GaAs(Si) by atomic hydrogen

    Page(s): 1181 - 1183
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    Atomic hydrogen in silicon‐implanted GaAs samples is studied by photoluminescence. The near‐band‐gap luminescence of GaAs samples subjected to a hydrogen plasma reveals the neutralization effect of the shallow donors. The photoluminescence intensity increases after hydrogen plasma treatment. However, the donor‐related luminescence is drastically reduced, indicating a smaller shallow donor concentration. After a thermal anneal (400 °C, 15 min), the original intensities of donor‐related lines are restored. We confirm the model of an electrically inactive hydrogen‐donor complex and rule out compensating defects created by the plasma treatment. View full abstract»

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  • Photoluminescence of Mg‐doped GaAs grown by molecular beam epitaxy using Mg3As2 as a Mg source: A comparison with Mg+ ion implantation

    Page(s): 1184 - 1186
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    Photoluminescence spectra of Mg‐doped GaAs grown by molecular beam epitaxy (MBE) are for the first time reported. Mg was introduced during MBE growth by using a synergic reaction of Mg3As2. Two near‐band‐edge emissions, g and [g‐g], were observed below bound exciton emissions which were originally obtained in Mg+ ion‐implanted GaAs. It is explicitly demonstrated that there is no essential difference of photoluminescence spectra between Mg+ ion‐implanted GaAs and the present material. These results conclusively indicate that the above two emissions are definitively related with the acceptor levels and exclusively not associated with crystalline defects produced by ion implantation. It is additionally presented that [g‐g] is principally established also in Mg‐doped GaAs prepared by liquid phase epitaxy, where [g‐g] is significantly suppressed due to the unintentional incorporation of Si donor atoms. For moderately Mg‐doped GaAs prepared by MBE a new fine emission with a doublet structure, temporarily denoted by AX, is obtained 5 meV below (A0, X) a bound exciton emission at neutral acceptors. View full abstract»

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  • Observation of a quasi‐two‐dimensional electron gas at an InSb/CdTe interface

    Page(s): 1187 - 1189
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    Liquid‐helium temperature transport and magnetotransport measurements on n‐CdTe grown by molecular beam epitaxy on p‐InSb substrates have demonstrated the presence of a quasi‐two‐dimensional electron gas in the InSb at the InSb/CdTe interface. The electron density and mobility in the channel can be varied by back gating. View full abstract»

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  • Determination of As and Ga planes by convergent beam electron diffraction

    Page(s): 1190 - 1192
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    Convergent beam electron diffraction using either the (200) systematic row and/or the (011) zone axis was successfully applied to determine the crystal polarity in (011) GaAs samples. This method makes it possible to distinguish the stacking sequence of the As and Ga planes. The information existing in the 200 disk of the diffraction pattern is different, depending on whether a particular disk refers to the As or the Ga plane. Therefore, this method can be generally applied in transmission electron microscopy for in situ samples and without any chemical etching. View full abstract»

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  • Improved recombination lifetime of photoexcited carriers in GaAs single quantum well heterostructures confined by GaAs/AlAs short‐period superlattices

    Page(s): 1193 - 1195
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    Photoluminescence (PL) decay time measurements at 77 and 300 K are reported from 6.1 nm GaAs single quantum well heterostructures (SQWH’s) confined by GaAs/AlAs short‐period superlattices (SPS’s) or ternary AlGaAs alloys with similar Al content, prepared by molecular beam epitaxy. The SQW PL intensity exhibits a single exponential decay with a time constant of 1.6 ns for SQWH’s confined by SPS’s and 0.3 ns for SQWH’s confined by AlGaAs alloys at 77 K. From comparison of the decay rates in both types of the sample, it is found that the radiative recombination efficiency is improved by a factor of about 6 in SPS confined SQWH’s. This higher efficiency is attributed to the improved heterointerfaces in addition to the enhanced radiative recombination rate due to the increased overlap of electron and hole wave functions in the narrow SQW. View full abstract»

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  • Degenerate four‐wave mixing from layered semiconductor clusters in the quantum size regime

    Page(s): 1196 - 1198
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    We report the first measurement of the third‐order nonlinear susceptibility χ(3) in layered semiconductor clusters exhibiting pronounced quantum size effects at room temperature. BiI3 clusters prepared in colloidal form in acetonitrile had a thickness of ≂7 Å and lateral dimensions between 60 and 90 Å. Using degenerate four‐wave mixing, we observed that the conjugate pulses from the small and the large gratings had comparable intensities, verifying the electronic origin of the nonlinearity. The nonlinear susceptibility was found to be 2.3×10-11 esu for a colloid with a cluster volume fraction of 10-5. View full abstract»

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  • Ultrathin InAs/GaAs single quantum well structures grown by atomic layer epitaxy

    Page(s): 1199 - 1200
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    Extremely thin InAs/GaAs single quantum well structures have been grown by atomic layer epitaxy. The wells were 2 and 4 InAs monolayers thick. Photoluminescence spectra (19 K) from these structures are sharp, intense, and uniform across the sample with full widths at half‐maximum for the 2 and 4 monolayer wells of 12 and 17 meV, respectively. These results indicate the high degree of control inherent in atomic layer epitaxy as well as its ability to grow high quality materials. 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