By Topic

Applied Physics Letters

Issue 1 • Date Jul 1996

Filter Results

Displaying Results 1 - 25 of 49
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (33 KB)  
    Freely Available from IEEE
  • An optically pumped GaN–AlGaN vertical cavity surface emitting laser

    Page(s): 1 - 3
    Save to Project icon | PDF file iconPDF (80 KB)  

    An optically pumped GaN‐based vertical cavity surface emitting laser (VCSEL) is demonstrated. Laser emission near 363 nm is observed at room temperature from the surface of a VCSEL structure optically pumped along a cleaved sample edge by focused light from a nitrogen laser. The VCSEL structure, which was grown on a sapphire substrate by metalorganic vapor phase epitaxy, consists of a 10 μm GaN active region sandwiched between 30‐period Al0.40Ga0.60N–Al0.12Ga0.88N Bragg reflectors. At optical pump intensities above ∼2.0 MW/cm2, a narrow (≪5 Å) laser mode at 363.5 nm emerges from the GaN photoluminescence spectrum. This mode becomes the dominant feature of the spectrum at higher pump powers, and additional modes appear ∼1.3 nm above and below this mode at 362.1 nm and 364.8 nm. The ∼1.3 nm mode spacing corresponds closely with the 1.1 nm spacing predicted from an electromagnetics model of the VCSEL structure. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electroluminescence from Au/Si nitride film/Si with the film prepared by electron cyclotron resonance method

    Page(s): 4 - 6
    Save to Project icon | PDF file iconPDF (50 KB)  

    We use only nitrogen as the reaction gas to deposit on the cleaned Si wafer an extra‐thin Si nitride film (∼40 Å) by electron cyclotron resonance method. Electroluminescence (EL) with its peak wavelength at about 7000 Å from the semitransparent Au/extra‐thin Si nitride film/p‐Si structure has been detected. The effects of forward bias and annealing on the EL have been studied. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Controlling polarization of vertical‐cavity surface‐emitting lasers using amorphous silicon subwavelength transmission gratings

    Page(s): 7 - 9
    Save to Project icon | PDF file iconPDF (61 KB)  

    Control of the polarization of vertical‐cavity surface‐emitting lasers (VCSELs) using a 240‐nm‐thick amorphous silicon subwavelength transmission grating (SWTG) is demonstrated. The grating, which has a strong polarization dependent reflectance and transmittance, was placed in front of the output window of a VCSEL. It was found that the SWTG can fix the VCSEL’s polarization in the direction perpendicular to the grating fingers, switch polarization directions, enhance the polarization ratio from 20:1 to over 200:1, and decrease the threshold current. Integration of these gratings into the VCSEL structure is discussed. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Laser operation of an Nd:Gd3Ga5O12 thin‐film optical waveguide fabricated by pulsed laser deposition

    Page(s): 10 - 12
    Save to Project icon | PDF file iconPDF (66 KB)  

    We report the laser operation of a thin‐film waveguide structure grown by the pulsed laser deposition technique. A 2.7‐μm‐thick crystalline film of neodymium doped Gd3Ga5O12 (Nd:GGG) lases at a wavelength centered at 1.06 μm when pumped by a Ti:sapphire laser at 808 nm. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electro‐optic properties of the organic salt 4‐N,N‐dimethylamino‐4′‐N′‐methyl‐stilbazolium tosylate

    Page(s): 13 - 15
    Save to Project icon | PDF file iconPDF (83 KB)  

    We show that the organic salt 4‐N,N‐dimethylamino‐4′‐N′‐methyl‐stilbazolium tosylate (DAST) is a very interesting material for electro‐optic applications in the near infrared. The electro‐optic coefficients, namely r111, r221, r331, r113, r223, and r333, were determined in the spectral range of 700 up to 1535 nm using optical samples cut from large high quality bulk crystals. DAST combines large electro‐optic coefficients, e.g., r111=77±8 pm/V at λ=800 nm and r111=47±8 pm/V at λ=1535 nm, with low dielectric constants, e.g., ϵ1=5.2±0.4. This combination leads to large polarization‐optical coefficients. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High‐speed and high‐sensitivity silicon‐on‐insulator metal‐semiconductor‐metal photodetector with trench structure

    Page(s): 16 - 18
    Save to Project icon | PDF file iconPDF (808 KB)  

    The frequency response and quantum efficiency (QE) of silicon‐on‐insulator (SOI) metal‐semiconductor‐metal photodetectors in the near‐infrared (∼800 nm) are greatly enhanced with a simple reactive ion etching to form electrodes inside the interdigitated trenches. Detectors with 1.25 μm trench spacing were fabricated on a SOI substrate with a 6‐μm‐thick silicon top layer. The unique device structure isolates carriers generated deep inside the semiconductor substrate and at the same time provides a highly uniform electric field throughout the active region of the detector, resulting in an instrumentation limited response time of 23 ps at 5 V bias and a -3 dB bandwidth of 2.3 GHz as measured at 790 nm. The dc responsivity is 0.12 A/W, corresponding to an external QE of 18.7% and an internal QE of 88.5%. The large bandwidth and good responsivity at the wavelength of interest, combined with their low operating voltages, make these detectors attractive for use in short‐distance optical communication systems. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microstructure of laterally oxidized AlxGa1-xAs layers in vertical‐cavity lasers

    Page(s): 19 - 21
    Save to Project icon | PDF file iconPDF (232 KB)  

    We have studied the lateral oxidation of AlxGa1-xAs (x=0.98 and 0.92) layers contained in vertical‐cavity lasers using cross‐sectional transmission electron microscopy. We find a fine‐grained (∼4 nm) cubic spinel phase of Al2O3 in both the 2% Ga‐ and 8% Ga‐oxidized layers. The 8% Ga‐oxidized layers contract vertically by 6.7% and not the expected 20% for a fully dense Al2O3 layer, with the 2% Ga‐oxidized layers showing a similar contraction. We observe a ∼17‐nm‐thick amorphous interface between the oxidized and unoxidized AlxGa1-xAs layers, which may account for the excellent electrical properties of these devices. We also observe metastable amorphous cavities associated with the moving reaction front. We infer the reaction proceeds from an initial amorphous phase that then transforms to a porous γ‐Al 2O3 layer. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurements of density fluctuations by modulation spectroscopy

    Page(s): 22 - 24
    Save to Project icon | PDF file iconPDF (78 KB)  

    Theoretical and experimental results describing the application of wavelength modulation spectroscopy to density fluctuations are given. The effects of concurrent amplitude modulation, which often occurs when such experiments are performed with diode lasers are accounted for. It is shown that the characteristics of the signal magnitude at line center as a function of density include the expected increase with density, n, in the Doppler regime. In the effective collision broadened regime the signal magnitude at line center falls approximately as n-N, where N is the order of the harmonic at which detection is performed. This result incorporates the well‐known result for direct absorption (N=0) in which the signal magnitude at line center stays constant while the linewidth increases in the collision broadened regime. It is shown that the sensitivity to density fluctuations measured by wavelength modulation spectroscopy around any ambient value depends strongly on the order of the detection harmonic employed, and that in many instances this sensitivity can be increased by using detection harmonics of order greater than the commonly used second order. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of annealing on the structure and dielectric properties of BaxSr1-xTiO3 ferroelectric thin films

    Page(s): 25 - 27
    Save to Project icon | PDF file iconPDF (80 KB)  

    The effect of a postdeposition anneal on the structure and dielectric properties of epitaxial BaxSr1-xTiO3 (BST) thin films (x=0.35–0.65) have been measured. The films were grown by pulsed laser deposition on LaAlO3 (001) substrates. The films were single phase and (001) oriented with a lattice parameter larger than the bulk. The dielectric properties of the x=0.35 film exhibited a broad temperature dependence and a peak at 168 K, which is 36 K below the peak observed in bulk BST (x=0.35). Annealing films for 8 h in flowing oxygen at 900 °C caused the lattice parameter to decrease and dielectric properties to become more like the bulk. Annealing also resulted in an increased electric field dependent dielectric tuning without increased dielectric loss. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Production of Eδ center induced by dry heat treatment of nonburied SiO2 films

    Page(s): 28 - 30
    Save to Project icon | PDF file iconPDF (75 KB)  

    Electron paramagnetic resonance data demonstrate that Eδ, a radiation‐induced defect consistently found in buried oxide films, can also be generated in nonburied oxides after heat treatment in a sufficiently dry ambient. The center appears in samples heated in either N2 or O2 with moisture content on the order of 1 part per million. The near equality of the number of Eδ centers in the N2 and O2 treated samples implies that the presence of O2 does not reduce the number of precursor defects. The results suggest that the center is related to a deficiency of hydrogen‐related species in the ambient rather than an O 2 deficiency as has been previously suggested. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Giant acoustic stop bands in two‐dimensional periodic arrays of liquid cylinders

    Page(s): 31 - 33
    Save to Project icon | PDF file iconPDF (132 KB)  

    Periodic binary systems can give rise to complete acoustic band gaps (i.e., stop bands) within which sound and vibrations are forbidden. We compute the band structure for two‐dimensional (2D) periodic arrays of long water cylinders surrounded by mercury host. Complete acoustic stop bands are found for both square and hexagonal lattices. We emphasize that such a simple 2D inhomogeneous system of liquids exhibits the widest stop bands ever reported for elastic as well as dielectric composites. We find gap/midgap ratios as high as ∼1. For mercury cylinders surrounded by water the gaps obtained are much smaller. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Self‐screening of the ferroelectric polarization in smectic C* cells in the bookshelf geometry

    Page(s): 34 - 36
    Save to Project icon | PDF file iconPDF (73 KB)  

    Surface stabilized ferroelectric liquid crystal (SSFLC) displays made of chiral smectic C* liquid crystals often present screening effects generally discussed in terms of the depolarizing field produced by ions attracted close to the electrodes. Here, we analyze the screening properties of distortions in the director field that form close to the electrodes because of the anchoring conditions. We show that the ferroelectric polarization effectively measured in such SSFLC cells is smaller than the real one, and depends on the spacing distance between the plates. Corrections are, therefore, necessary for samples of thickness ≪10 μm. This screening mechanism, which moreover increases the bistability of the cell, is as fast as the polarization reversal itself contrarily to the screening due to ion migrations. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improvement of the Young’s modulus of SiC film by low‐pressure chemical vapor deposition with B2H6 gas

    Page(s): 37 - 39
    Save to Project icon | PDF file iconPDF (64 KB)  

    SiC is one of the potential materials for use as an x‐ray mask substrate. It is preferable for an x‐ray mask substrate to have a large elastic modulus, so as to suppress any distortion of the extremely minute and precise patterns. The improvement of the Young’s modulus of polycrystalline SiC film using low‐pressure chemical vapor deposition with the introduction of B 2H6 in the source gas was investigated. The Young’s modulus increased with the addition of B2H6, and a maximum value of 600 GPa, which was 25% higher than in the case without B2H6, was reached at a source gas ratio B/Si=0.02. Two models which would possibly explain this phenomenon are discussed, and the theory which takes into account the interaction between carrier and ion core is found to provide a more plausible explanation of the results. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thermal analysis using a micromechanical calorimeter

    Page(s): 40 - 42
    Save to Project icon | PDF file iconPDF (720 KB)  

    A fast and extremely sensitive method for reversible thermal analysis of picoliter volumes of solid samples is presented. Using a micromechanical calorimeter based on the deflection of a bimetallic cantilever, enthalpy changes at phase transitions in n‐alkanes (paraffins) are determined. The key role of volume changes associated with phase transitions is discussed together with a method to separate thermal and volume‐induced stresses associated with these phase transitions. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Degrees of visible determinism in crystal growth striations as a measure of crystal quality

    Page(s): 43 - 45
    Save to Project icon | PDF file iconPDF (71 KB)  

    A diagnostic test based on the parallelism of neighboring trajectories generated from a time series in phase space for visible determinism is applied to characterizing complexities in growth striations of Czochralski silicon crystals. Change in the structure of the striations by crystal annealing is examined in terms of degrees of randomness in growth striations. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Phase identification of boron nitride thin films by polarized infrared reflection spectroscopy

    Page(s): 46 - 48
    Save to Project icon | PDF file iconPDF (66 KB)  

    Six different types of boron nitride films were investigated by polarized infrared reflection spectroscopy. Films with a highly cubic, mixed cubic and noncubic, and exclusively noncubic phase composition were synthesized using ion beam assisted deposition. Additionally, postdeposition argon ion irradiated cubic and noncubic boron nitride films as well as a nitrogen implanted boron sample were analyzed. Using this technique, besides the cubic phase, two different noncubic modifications, layered anisotropic and amorphous, could be distinguished. A preferential orientation of the normal axis of the sp2‐bonded basal planes parallel to the substrate surface was observed. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Diamond‐like carbon films grown by very high frequency (100 MHz) plasma enhanced chemical vapor deposition technique

    Page(s): 49 - 51
    Save to Project icon | PDF file iconPDF (53 KB)  

    Diamond‐like carbon films were grown by VHF‐PECVD technique. Since the self‐bias potential developed in a VHF plasma is very low, sufficiently high negative dc voltage was applied to the substrates in order to make DLC film being grown reasonably hard. Also a comparative study of VHF grown films was made with rf (13.56 MHz) discharge grown films (grown in the same PECVD reactor). This made it possible to investigate the specific effects of excitation fre‐ quency while keeping other parameters constant. Deposition rate (rd) was found to be about 5 times higher for VHF grown films. Marginal variation in optical band gap (Eg) and refractive index (n) were observed in VHF grown films with variation in deposition parameters. Maximum value of hardness recorded was 1500 kg/mm2 in the case of rf and 902 kg/mm2 in the case of VHF grown films, within the range of deposition parameters. Stress values were in the range 1.7×109-2.9×109 Nm-2 for VHF and 3.6×109-4.6×109 Nm-2 for rf grown films. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Low temperature current imaging tunneling spectroscopy on wet chemically etched quantum wires

    Page(s): 52 - 54
    Save to Project icon | PDF file iconPDF (1568 KB)  

    In this letter, low temperature current imaging tunneling spectroscopy studies on wet chemically etched quantum wires are reported. On the wires, symmetric current voltage curves are observed. Between the wires, however, significant current is only observed for negative sample bias. Through this behavior, topographic and current imaging profiles of quantum wires are obtained. In liquid helium, the current profiles of the wires are clearly smaller than the topographic profiles, which is used to determined the edge depletion width directly. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High temperature adduct formation of trimethylgallium and ammonia

    Page(s): 55 - 57
    Save to Project icon | PDF file iconPDF (73 KB)  

    High temperature gas phase reactions between trimethylgallium (TMG) and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure, and reaction time were chosen to emulate the gas phase environment typical of the metal–organic vapor phase epitaxy (MOVPE) of GaN. The main gas phase species is [(CH 3)2Ga:NH2]x, where most probably x=3, resulting from the very fast adduct formation followed by elimination of methane. The further gas phase decomposition of this species proceeds through the stepwise elimination of methane. These studies indicate that little TMG exists within the growth ambient under most MOVPE growth conditions. The further gas phase reaction of [(CH3)2Ga:NH 2]x may be responsible for the strong dependence of the MOVPE GaN growth rate and uniformity commonly observed. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Radiation enhanced diffusion of low energy ion‐induced damage

    Page(s): 58 - 60
    Save to Project icon | PDF file iconPDF (65 KB)  

    We have investigated the influence of concurrent above‐band‐gap laser illumination on the damage profile of GaAs/AlGaAs heterostructures subject to low energy (sub‐keV) Ar+ ion bombardment. A dramatic change in damage profile was observed for these samples, compared with those that were not laser illuminated, and the degradation increases with the illuminated power intensity. Below‐band‐gap illumination results in a minimal increase in damage profile. Such results indicate the possibility of radiation‐enhanced diffusion of defects, and may explain the observed high defect diffusivity at room temperature. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • GaAs/AlGaAs quantum wires fabricated by SiO2 capping‐induced intermixing

    Page(s): 61 - 63
    Save to Project icon | PDF file iconPDF (151 KB)  

    We demonstrate that selective intermixing of GaAs/AlGaAs quantum well heterostructures induced by SiO2 capping and subsequent annealing can be spatially localized on a length scale compatible with the lateral confinement of carriers into quantum wires. Low temperature optical spectroscopy measurements including linear polarization anisotropy analysis show evidence of the formation of one‐dimensional subbands. A mechanism involving the ability of the thermal stress field generated in the heterostructure by the patterned SiO2 film to pilot the diffusion of the excess Ga vacancies, which are responsible for the enhanced interdiffusion under SiO2 is suggested to account for the high lateral selectivity achievable with this novel process. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of carbon on strain relaxation and phase formation in the Ti/Si1-x-yGexCy/Si contact system

    Page(s): 64 - 66
    Save to Project icon | PDF file iconPDF (201 KB)  

    We report the first study of interfacial reactions of a metal with Si1-x-yGexCy epitaxially grown on Si. The Ti/Si1-x-yGexCy/Si (0≪y≪1.7%) contact system was studied after isochronal heat treatments from 500 to 800 °C. The results for Ti/Si1-xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide–germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide–germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide–germanide/epilayer interface was detected for the C‐containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Anomalous surface segregation of Sb in Si during epitaxial growth

    Page(s): 67 - 69
    Save to Project icon | PDF file iconPDF (72 KB)  

    A delta‐function‐shaped Sb doping spike in Si is prepared by deposition of Sb on Si(001) followed by low‐temperature molecular beam epitaxy of Si. The depth profile of the Sb atoms is measured using high‐resolution Rutherford backscattering spectroscopy, yielding a depth resolution of 0.3 nm. The observed profile shows two peaks corresponding to the δ‐doped layer (of width 0.5 nm) and Sb atoms on the surface. The latter are due to surface segregation of Sb atoms during the growth of the Si cap layer. The surface segregation rate is derived from the observed results at temperatures 70–280 °C. It is larger than the value extrapolated from high‐temperature (≳400 °C) data by several orders of magnitude and shows a very weak temperature dependence as compared to the high‐temperature data. These features indicate a new surface segregation mechanism at low temperature. A mechanism for this anomalous segregation is discussed. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical detection of charge carriers in organic light‐emitting diodes

    Page(s): 70 - 72
    Save to Project icon | PDF file iconPDF (49 KB)  

    A modulation technique is described to measure the optical absorption due to majority carriers (holes) in single layer and bilayer organic light‐emitting diodes. It allows determination of the space‐charge density inside the device at a given current, the time response of the system and the charge carrier mobility. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor
Nghi Q. Lam
Argonne National Laboratory