By Topic

Applied Physics Letters

Issue 1 • Date Jan 1991

Filter Results

Displaying Results 1 - 25 of 37
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (152 KB)  
    Freely Available from IEEE
  • Single‐mode polymer waveguide modulator

    Page(s): 1 - 3
    Save to Project icon | PDF file iconPDF (338 KB)  

    We report herein the first single‐mode polymer waveguide modulator which can be formed on any surface regardless of its conductivity and refractive index. These include semiconductor, conductor, and insulator surfaces. The tunability of the refractive index of the polymer film allows us to shift the guiding layer from a stepped index profile to a graded index profile. The phase‐matching condition for optical power transfer is achieved through current‐induced index modulation. Thirty‐six dB extinction ratio, which includes 3 dB absorption loss and 33 dB phase‐matched cross coupling, was observed with a current injection density of ∼1.8 μA/μm2. Unlike the conventional symmetrical dual channel coupler, the disparity of the collinear waveguide pair provides us with a much larger dynamic range of waveguide dimension suitable for generating the required phase‐matching condition and thus easing the requirement of waveguide fabrication. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Differential gain of GaAs/AlGaAs quantum well and modulation‐doped quantum well lasers

    Page(s): 4 - 6
    Save to Project icon | PDF file iconPDF (402 KB)  

    The differential gain which is an important parameter for modulation dynamics in semiconductor lasers is evaluated experimentally by measuring the gain coefficient and the carrier lifetime in GaAs/AlGaAs double‐heterostructure (DH) lasers, quantum well (QW) lasers, and p‐modulation‐doped quantum well (p‐MDQW) lasers. The results indicate that the differential gain of the QW laser is 2.4 times as high as that of the DH laser, which is consistent with the theory. In addition, it is found that improvement of the differential gain using the p‐MDQW structure is not so large as that expected by the theory. This result suggests that enhanced energy broadening due to the reduction of the equivalent dephasing time τeqin, which includes both the dephasing time τin due to the intraband relaxation and the band tailing effects, significantly affects the gain spectra in the p‐MDQW lasers, which is confirmed by the measurement of the spontaneous emission spectra. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Pseudomorphic InyGa1-yAs/GaAs/AlxGa1-xAs single quantum well surface‐emitting lasers with integrated 45° beam deflectors

    Page(s): 7 - 9
    Save to Project icon | PDF file iconPDF (430 KB)  

    We report on the first demonstration of pseudomorphic InGaAs single quantum well surface‐emitting lasers (SELs), with etched vertical mirrors and integrated 45° beam deflectors fabricated by ion beam etching. 100‐μm‐wide broad‐area SELs exhibited a threshold current of 320 mA, a total power of 126 mW, and a total external differential quantum efficiency of 0.09 W/A for a 500‐μm‐long cavity. The perpendicular far‐field pattern of broad‐area SELs showed a full width at half maximum of ∼20°. The lasers with various types of cavities fabricated from the same wafer were compared. Broad‐area edge‐emitting lasers had a threshold current of 200 mA, a total power of 700 mW, and a total external differential quantum efficiency of 0.52 W/A. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Calculations of a Ta soft x‐ray laser (44.8 Å) using a sub‐Kilojoule pump

    Page(s): 10 - 12
    Save to Project icon | PDF file iconPDF (259 KB)  

    A design is presented for a Ni‐like Ta x‐ray laser which uses less than 1 kJ pump energy. This is in contrast with previous experiments carried out at the Nova two‐beam chamber which have used several kJ pump energy. The main features of the new system are the use of a thin target (30 μg/cm2 Ta), a much lower intensity, and a shorter pulse. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement of nonlinear refractive index and transmission in polydiacetylene waveguides at 1.319 μm

    Page(s): 13 - 15
    Save to Project icon | PDF file iconPDF (350 KB)  

    Nonlinear optical measurements in strip‐loaded channel waveguides of poly(4‐BCMU) at 1.319 μm are reported. Using a pulse‐modulated interferometry method, the intensity‐dependent refractive index is found to have an electronic contribution, n2=(4.8±2.7)×10-8 cm2/MW, and an estimated thermal contribution, n2=-(7.9±4.5)×10-11 cm2/MW, for 60 pS laser pulses at 76 MHz. The two‐photon absorption coefficient β is less than 0.25 cm/GW. Figures‐of‐merit suggest that poly(4‐BCMU) has properties desirable for all‐optical devices, but that fabrication losses and thermal effects due to absorption will limit device performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High performance surface‐emitting lasers with 45° intracavity micromirrors

    Page(s): 16 - 18
    Save to Project icon | PDF file iconPDF (323 KB)  

    For the first time, high performance GaAs/GaAlAs surface‐emitting lasers with internal 45° micromirrors, which totally reflect and emit the beam from the substrate in junction‐down configuration, have been demonstrated. The 45° and 90° mirrors of the device were fabricated by using ion milling and reactive ion etching techniques, respectively. Typical threshold current density of 440 A/cm2, external differential efficiencies of 52%, and output power in excess of 1 W under quasi‐cw operation have been achieved. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fabrication and characterization of planar ion‐exchanged KTiOPO4 waveguides for frequency doubling

    Page(s): 19 - 21
    Save to Project icon | PDF file iconPDF (399 KB)  

    Optical waveguides can be formed in potassium titanyl phosphate (KTiOPO4, KTP) crystals by an ion‐exchange process. Waveguides were fabricated in KTP substrates by exchanging rubidium ions for potassium ions. The resulting refractive index profile was measured as a function of diffusion time and temperature. Based on these characterization measurements, the phase‐matching properties of the planar waveguide for guided‐wave second‐harmonic generation were modeled. Second‐harmonic generation of blue/green light was observed at wavelengths shorter than the bulk phase‐matching limit, in good agreement with the results of numerical modeling. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • cw high‐power diffraction‐limited‐beam operation from resonant optical waveguide arrays of diode lasers

    Page(s): 22 - 24
    Save to Project icon | PDF file iconPDF (387 KB)  

    Monolithic phase‐locked resonant arrays of antiguides, resonant optical‐waveguide (ROW) arrays, have been optimized for efficient in‐phase‐mode operation. Diffraction‐limited, in‐phase‐mode continuous‐wave (cw) operation is obtained from 20‐element uniform arrays to 250 mW output power, with (front facet) external differential quantum efficiencies of 41%. Single longitudinal mode operation is observed below 100 mW cw. In‐phase‐operating devices with and without Talbot‐type spatial filters are compared, and it is found that for ROW arrays Talbot‐type spatial filters are not required. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Power scaling of large‐aperture photoconducting antennas

    Page(s): 25 - 27
    Save to Project icon | PDF file iconPDF (334 KB)  

    We describe the power scaling and saturation properties of large‐aperture planar photoconducting antennas which emit and detect ultrashort terahertz electromagnetic pulses. At high optical fluences, the radiated electric field saturates at a value comparable to the bias field in agreement with a simple model of the radiation mechanism. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Novel integrated acousto‐optic and electro‐optic heterodyning device in a LiNbO3 waveguide

    Page(s): 28 - 30
    Save to Project icon | PDF file iconPDF (442 KB)  

    A wideband integrated optic heterodyning device that utilizes simultaneously a wideband acousto‐optic (AO) Bragg cell and a wide‐angle electro‐optic (EO) Bragg grating lens has been realized, for the first time, in a Y‐cut LiNbO3 waveguide 1×8×20 mm3 in size. The device has demonstrated a bandwidth of 240 MHz centered at 350 MHz and a single‐tone instantaneous and two‐tone third‐order spurious‐free dynamic ranges of 44.6 and 36.0 dB, respectively, at the optical wavelength of 0.6328 μm. The device suggests a new and simple architecture for wideband integrated optic interferometric rf spectrum analyzers. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rastered, uniformly separated wavelengths emitted from a two‐dimensional vertical‐cavity surface‐emitting laser array

    Page(s): 31 - 33
    Save to Project icon | PDF file iconPDF (389 KB)  

    We report the first two‐dimensional vertical‐cavity surface‐emitting laser (VCSEL) array with each laser emitting a unique, nonredundant wavelength. This was achieved by implementing spatially chirped layers in the VCSEL structure and obliquely aligning the array axes to the direction of the thickness chirp. We obtained 77 wavelengths from a 7×11 VCSEL array with all the lasers emitting single mode. Uniform wavelength separation between neighboring lasers is achieved with the direction of increasing wavelength rastering through the array. All the lasers exhibit nearly the same optical and electrical properties, in spite of the intentionally implemented difference in the emission wavelengths. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Composition dependence of the second‐harmonic phase‐matching temperature in LiNbO3

    Page(s): 34 - 35
    Save to Project icon | PDF file iconPDF (239 KB)  

    Phase‐matching temperatures for 90° phase matching of Nd:YAG laser light have been measured in LiNbO3 crystals with different Li/Nb ratios. Their melt and solid composition had been determined chemically with an accuracy of about 0.2%. Our results contrast to earlier work, no linear dependence of the phase‐matching temperature versus the Li/Nb ratio was found. The measured dependence shows that the phase‐matching temperature can be used as an excellent probe for the composition of LiNbO3. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Epitaxial growth and crystallographic analyses of (Pb, La)TiO3 thin films by a multi‐ion‐beam reactive cosputtering technique

    Page(s): 36 - 38
    Save to Project icon | PDF file iconPDF (278 KB)  

    Epitaxial thin films of lead titanate(PbTiO3) and lanthanium‐modified lead titanate [(Pb, La)TiO3] have been successfully grown on (0001) sapphire substrates for the first time by the recently developed multi‐ion‐beam reactive cosputtering (MIBRECS) technique. The deposition processes and the thin‐film analyses studied by x‐ray diffraction (XRD), electron probe x‐ray microanalyzer (EPMA), and reflection high‐energy electron diffraction (RHEED) are reported. The experiments show that the multi‐ion‐beam reactive cosputtering process is very suitable for deposition of multicomponent oxide thin films with high reproducibility. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hydrogen effusion from hydrogenated amorphous silicon caused by the deposition of a silicon nitride overlayer

    Page(s): 39 - 41
    Save to Project icon | PDF file iconPDF (350 KB)  

    The effect of silicon nitride (SiN) deposition on hydrogenated amorphous silicon (a‐Si:H) has been investigated to find the origin of the difference of a‐Si:H/SiN interface properties caused by the order of deposition. Sheet conductance of the on‐state in inverted staggered (a‐Si:H on SiN) thin‐film transistors (TFTs) increases gradually with the substrate temperature (Tsub) of SiN, but decreases rapidly with the Tsub of SiN in staggered TFTs (SiN on a‐Si:H). Photoluminescence experiments indicated that the degradation in staggered TFTs was due to the creation of defects in a‐Si:H by the deposition of the SiN overlayer. It was shown by Fourier transform infrared attenuated total reflection that the origin of the defects was hydrogen effusion from a‐Si:H. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electromigration in a single crystalline submicron width aluminum interconnection

    Page(s): 42 - 44
    Save to Project icon | PDF file iconPDF (375 KB)  

    Electromigration properties in a single crystalline submicron width aluminum interconnection formed on Si(111) have been examined by resistance change measurements and in situ observations using scanning electron microscopy. It was observed that single crystalline aluminum has an extremely high resistance to electromigration‐induced open circuit failures, when compared to polycrystalline copper and aluminum. The mechanism for the high resistance is considered to be a large activation energy, resulting from lattice diffusion. A tendency for void formation to become parallel to the longitudinal direction of the interconnection assisted the life time prolongation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Formation of amorphous interlayers by solid‐state diffusion in ultrahigh‐vacuum‐deposited polycrystalline Nb and Ta thin films on (111)Si

    Page(s): 45 - 47
    Save to Project icon | PDF file iconPDF (444 KB)  

    The formation of amorphous interlayers (a‐interlayers) in ultrahigh‐vacuum‐deposited polycrystalline Nb and Ta thin films on (111)Si has been studied by cross‐sectional transmission electron microscopy. The growth of a interlayers was found to follow a linear growth law initially in samples annealed at 450–500 °C and 550–625 °C for Nb/Si and Ta/Si, respectively. The growth then slows down and deviates from a linear growth behavior as a critical thickness of the a interlayer was reached. The a interlayer/crystalline Si interface was found to be rather smooth. The roughness of the interface between the Nb layer and a interlayer was observed to decrease with annealing temperature and time. The observation suggested that the growth of the a interlayer was interface reaction controlled initially. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dislocation velocity in indium phosphide

    Page(s): 48 - 50
    Save to Project icon | PDF file iconPDF (298 KB)  

    Velocities of α, β, and screw dislocations in InP crystals generated from surface scratches were measured as a function of stress and temperature by means of the etch pit technique. Effects of Zn and S impurities, acting as acceptor and donor, respectively, on the dislocation velocity were also investigated. lt was found that Zn impurity strongly retards the motion of all types of dislocations. On the other hand, S impurity is found to reduce the mobilities of β and screw dislocations while it enhances the mobility of α dislocations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Metal/semiconductive polymer Schottky device

    Page(s): 51 - 52
    Save to Project icon | PDF file iconPDF (249 KB)  

    Development of a metal/organic‐semiconductor Schottky junction as an alternative to the metal/inorganic‐semiconductor junction is reported. Metal/polypyrrole (PP) junctions have been prepared with electrochemically deposited doped PP films of different thickness and various metals (In, Sn, Ti, and Al) as electrodes. The electrical characteristics of the junction depend upon the work functions of PP and the metal. It has been possible to prepare Schottky barriers on the PP films with a metal electrode having a work function lower than that of the polymer. Various physical characteristics of the polymer, work function, Fermi level, and carrier concentration have been estimated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Disorder of ZnSe/ZnS strained‐layer superlattices by N+ or Li+ ion implantation and low‐temperature annealing

    Page(s): 53 - 55
    Save to Project icon | PDF file iconPDF (342 KB)  

    We demonstrate layer disordering of ZnSe/ZnS strained‐layer superlattices (SLSs) induced by low‐damage N+ or Li+ ion implantation and low‐temperature annealing. The interdiffusion of Se and S atoms was observed by secondary‐ion mass spectrometry analyses. By reflectance measurements, a significant decrease in the refractive index, which is useful for waveguiding applications, was measured in the disordered SLS. In photoluminescence (PL) spectra, strong excitonic emission around 400 nm was observed in the disordered SLS corresponding to a damage recovery. A slight red shift of the PL peak observed in the early stages of annealing is interpreted as the relaxation of misfit strain by interdiffusion. For longer annealing times, the PL peak for an implanted SLS shifted towards the higher energy side, which clearly indicates layer disordering of the SLSs. This low‐temperature planar process will be very useful for the fabrication of II‐VI semiconductor optoelectronic devices. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Controlled sublimation growth of single crystalline 4H‐SiC and 6H‐SiC and identification of polytypes by x‐ray diffraction

    Page(s): 56 - 58
    Save to Project icon | PDF file iconPDF (321 KB)  

    Polytype‐controlled crystal growth of SiC was carried out by using a sublimation method. Production yields as high as 80% and 85% for 4H and 6H single crystals were obtained, respectively. We observed in x‐ray diffraction pattern of SiC that space‐group‐forbidden peaks appear periodically among (000l) peaks. Their intensity is strong enough to be distinguished. These peaks represent the periodicity along the c axis of each polytypic modification of SiC. X‐ray diffractometry using these peaks is quite useful and easy for a clear identification of the SiC polytypes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dichlorosilane effects on low‐temperature selective silicon epitaxy

    Page(s): 59 - 61
    Save to Project icon | PDF file iconPDF (410 KB)  

    Low‐temperature selective silicon epitaxial growth using a dichlorosilane‐hydrogen mixture in a low‐pressure chemical vapor deposition hot‐wall reactor has been studied. A simple HF vapor treatment effectively removes surface oxides and passivates the Si surface prior to reactor loading. The addition of a small concentration of dichlorosilane to the H2 ambient during the prebake at a temperature of 900 °C improves selective epitaxial quality both by maintaining an oxide‐free surface, and by suppressing undercut of oxide‐covered regions. With these process improvements defect‐free, selectively overgrown Si epitaxial layers are achieved at deposition temperatures between 800 and 850 °C. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dose rate effects on damage accumulation in Si+‐implanted gallium arsenide

    Page(s): 62 - 64
    Save to Project icon | PDF file iconPDF (484 KB)  

    Ion‐induced damage accumulation has been measured as a function of ion dose and dose rate following 100 keV Si+ room‐temperature implants in GaAs. The dose rate has been found to have a strong effect on the total damage produced in GaAs over a range of dose between 1014 and 1015/cm2 and implantation current densities from 0.05 to 12 μA/cm2. Two distinct stages of damage formation have been identified. At low implantation doses, damage accumulates slowly and tends to saturate at a level of approximately 0.4×1017defects/cm2. However, beyond a threshold dose (≊1014 Si/cm2) which decreases with increasing dose rate, damage accumulates rapidly. In the second stage, the onset of which appears to be associated with the formation of more complex damage structures, the total damage and the damage accumulation rate were found to increase with dose rate for a fixed ion dose. For comparison, dose rate effects were also measured in Si and Ge under similar implant conditions and found to be weaker. The results for GaAs are correlated with recent observations of dose‐rate‐dependent electrical activation in Si‐implanted GaAs. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Limited thickness epitaxy in GaAs molecular beam epitaxy near 200 °C

    Page(s): 65 - 67
    Save to Project icon | PDF file iconPDF (471 KB)  

    The low‐temperature limit to GaAs molecular beam epitaxy (MBE) is studied at temperatures from 250 °C to room temperature. Using transmission electron microscopy of layers grown under a variety of conditions we show that, as for Si MBE, there is an epitaxial thickness hepi at which a growing epitaxial layer becomes amorphous. The temperature, growth rate, composition, and defect density all appear to be constant during growth of the epitaxial layer, and (in analogy with Si MBE) we tentatively associate the breakdown of epitaxy at hepi with roughening of the growth surface. We demonstrate that hepi depends strongly on composition, increasing rapidly with Ga/As ratio at fixed temperature. At fixed Ga/As ratio, hepi shows an abrupt increase from ≪200 to ≳5000 Å at 210 °C. The results have implications for the growth of GaAs/GaAs for high‐speed photodetectors, as well as possible applications to GaAs/Si heteroepitaxy. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electron spin resonance of antisite defects in as‐grown and plastically deformed GaP

    Page(s): 68 - 70
    Save to Project icon | PDF file iconPDF (385 KB)  

    In as‐grown GaP we investigated two phosphorous antisite related electron spin resonance spectra with respect to ligand hyperfine (lhf) interactions: basing upon a linewidth analysis, we attribute a hyperfine doublet with unresolved lhf structure (PA3) in n‐GaP:S to a P‐antisite defect with cubic symmetry. The lhf interaction of the well known lhf resolved PP4 doublet (PA1) in semi‐insulating GaP:Cr was found to be temperature dependent. In plastically deformed GaP the two spectra showed contrary linewidth changes. In highly deformed n‐GaP:S both signals were detectable. A new spectrum of low symmetry (GA1) was observed which we attribute to a gallium antisite related defect. 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