摘要:

Time‐integrated emission spectra from the pulsed discharge of a 3.5‐MeV electron beam, with 90‐kA peak current of about 30‐nsec duration, and guided by a glass rod protruding from the cathode in a field‐emitting diode, have been studied with a quartz‐prism spectrograph. With anodes of graphite or polyethylene, the spectrum in the near‐uv to visible range is found to consist mainly of emission lines from C, C+, C++, and C+3, and similar ones from silicon. The spatial dependence of emission intensity indicates that a hot spot is present during the discharge near the anode surface. The temperature and the electron density in the plasma are estimated through a theoretical analysis of the composition of carbon in the gas phase.

ISSN:0021-8979    

DOI:10.1063/1.1663563

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Factors that are important in maintaining zero‐order‐mode operation at high power in large‐cavity GaAs double‐heterostructure lasers are described. In the first place, it had previously been shown that the electronic gain of the zero‐order mode is larger than that of high‐order modes when gain is restricted to two‐thirds of the waveguide thickness, and the remaining one‐third is kept lossy. In practice, this is realized by the LPE growth of a heteroboundary within the cavity such that (a) by the addition of a small amount of aluminum the band gap of the umpumped region is made larger (≈40 meV) than that of the gain region and (b) the umpumped region is doped with a donor concentration larger than the electron concentration in the gain region at lasing threshold. The second factor that is useful in maintaining zero‐order‐mode operation at high power levels is the use of a zero‐order‐mode antireflective (AR) coating that increases the mirror transmission loss for the undesired high‐order modes. This zero‐order‐mode selective AR coating consists of layers of ZnS and Al2O3whose thicknesses are accurately controlled to provide maximum transmission loss at some prescribed angle of emergence relative to the normal axis. Experimental results obtained on zero‐order‐mode large‐cavityPpnNlasers substantiate these design considerations.

ISSN:0021-8979    

DOI:10.1063/1.1663564

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The gain of the CF3I iodine photodissociation laser is observed to decrease exponentially with time. The decay rate increases dramatically with a small increase in flashlamp energy. Assuming that the rise in the gas temperature increases as the flashlamp energy is increased, this indicates that the process causing the decrease in the gain has an activation energy. It appears that CF3I pyrolysis is the source of the loss in gain, and from the observed decay rate the gas temperature is calculated to be about 1200°K. Measurement of the late‐time iodine‐iodine recombination rate also yields this temperature. The stimulated‐emission cross section measured under the same conditions is (2.6±0.5)×10−18cm2.

ISSN:0021-8979    

DOI:10.1063/1.1663565

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Modified Schottky barriers of the type Au&sngbnd;CdS : Cu were prepared by diffusing Cu to a depth of 0.1–0.2 &mgr;m into single crystals of CdS, prior to evaporating rectifying Au contacts. The electronic and photoelectronic properties of these junctions are adequately described by a simple model in which the Cu acts as an ionized acceptor, resulting in a ``humped'' potential barrier between the Au and the bulk CdS. Hole trapping by the acceptors under band‐gap illumination reduces their ionization and, consequently, the hump height. The forward current density in the dark and under illumination can be accurately described by a thermionic emission model asJ=A*T2exp {—e[VB+VH(0)]/kTexp}(eV/&bgr;kT), where the hump potentialVH(0) is light sensitive and where &bgr; (1<&bgr;<1.35) arises from a weak voltage dependence of the barrier height. Barrier height determinations, in the dark and under illumination with 5000‐Å light, by means of internal photoemission, thermal activation energy, andJ‐Vmeasurements unequivocally show that under saturating light conditions the hump in the potential barrier is reduced by 0.23±0.03 V. This barrier mechanism of photoconductive response results in steady‐state electron/photon gains in excess of 106at light intensities lower that 5×1011photons cm−2sec−1, where response times exceed 1 sec.

ISSN:0021-8979    

DOI:10.1063/1.1663566

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A method is described for the determination of the nitrogen concentration in GaP crystals from optical absorption measurements. The method has been calibrated by measuring the absolute nitrogen concentration by nuclear reaction quantitative analysis in the same samples for which the optical absorption was measured. The relationships between the nitrogen concentration, the integrated absorption of theAline (2.3172 eV), and the optical absorption atAx(2.3275 eV) at 4.2°K are given by [N] cm−3=8.5×1014∫&agr;Ad E=3.4 ×1016&agr;Ax, where &agr; is measured in cm−1andd Ein meV. Previous formulas which have commonly been used to determine the nitrogen concentration in terms of optical absorption overestimate the nitrogen concentration by about a factor of 5. Also the application of these formulas has varied between laboratories. Section I describes the determination of nitrogen concentrations by nuclear microanalysis. Measurements have been made in the range from[inverted lazy s]5×1016to[inverted lazy s]1018 cm−3in GaP grown by the liquid encapsulated Czochralski process in a nitrogen‐pressurized crystal puller and in nitrogen‐doped GaP grown by liquid phase epitaxy at [inverted lazy s]1000°C. Two distinct charged‐particle techniques have been employed. In crystals containing nitrogen of normal isotopic composition, the14N concentration was determined by proton activation using the reaction14N(p,&agr;)11C with proton energies in the range 6–10 MeV. The reaction product,11C, was chemically separated after irradiation. The11C is a positron emitter, and the &ggr; rays from the positron annihilation were measured. Boron interference through the reaction11B(p,n)11C was independently determined by measuring the prompt &agr;‐particle emission from the reaction11B(p,&agr;1)8Be*→2&agr;2during irradiation with 685‐keV protons. In15N‐doped LPE layers, the15N concentration was determined by measuring the prompt &agr;‐particle emission from the reaction15N(p,&agr;)12C during irradiation with 685‐keV protons. Section II describes the optical absorption measurements and the correlation with the nuclear measurements. The temperature dependence of the integrated absorption and the line shape of theAline have also been measured. For determination of the nitrogen concentration, theA‐line absorption measurements should be made at a temperature at which the absorption line shape is amenable to accurate integration. The integrated absorption can then be corrected to its value at 4.2°K and the nitrogen concentration calculated from the above relationship.

ISSN:0021-8979    

DOI:10.1063/1.1663567

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The structure and resistivity of vanadium dioxide films close to the metal‐semiconductor transition have been studied as a function of stoichiometry. Unit‐cell volume is shown to go through a minimum and the transition temperature and resistivity ratio through a maximum at the apparent stoichiometric oxygen level. The observed resistivities can be accounted for by an increased electron concentration due to vanadium interstitials in the low‐oxygen films and by a second phase in the high‐oxygen films. The variation of resistivity and transition temperature with electron concentration provides experimental support for the previous suggestion that the driving force of the transition is mainly an antiferroelectric distortion.

ISSN:0021-8979    

DOI:10.1063/1.1663568

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Volumetric irradiation by a short‐pulse electron beam has been used to trigger long‐duration spatially uniform electric discharges in gas mixtures of He and F2or SF6. Uniform energy deposition to 300 J/liter has been observed for atmospheric F2&sngbnd;He mixtures at nominal electron‐beam currents of 3 A/cm2and discharge currents up to 20 A/cm2. Operation suitable for efficient initiation of pulsed HF/DF chain lasers appears possible over a wide range ofE/Nand mixture ratios, limited by breakdown at largeE/Nand negligible field enhancement at lowE/N. Approximate analytical plasma models are presented and used in conjunction with time‐resolved afterglow current measurements to obtain rate constants for F−‐ionF2+−ionrecombination andF2+−ionelectron recombination. Estimates of F2dissociation fractions achieved in the experiments imply the possibility of scalable and efficient initiation of pulsed chemical lasers with such discharges.

ISSN:0021-8979    

DOI:10.1063/1.1663569

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The phase modulation due to the linear electro‐optic effect of GaAs&sngbnd;AlxGa1−xAs double‐heterostructure (DH)p‐njunction diode light modulators can be a strong function of the applied bias voltage. The observed nonlinear voltage dependence of the phase difference &Dgr;&phgr; between the phases of the TE and TM modes is in good agreement with the predictions of a mathematical dielectric slab waveguide model with five stepwise constant dielectric layers, if a suitably defined average junction electric field is used. The magnitude of &Dgr;&phgr; and its nonlinear voltage dependence measurably depend on the properties of the optical dielectric waveguide and on thep‐njunction doping profile. Within the accuracy of our measurements, we have not been able to identify contributions due to higher‐order electro‐optic effects. Our results emphasize that large modulation effects and good modulation linearity of &Dgr;&phgr; modulation can be achieved by appropriately controlledp‐njunction doping profiles. Conversely, &Dgr;&phgr; measurements as a function of bias provide a novel tool for studyingp‐njunction doping profiles and for determining the Al concentration of the AlxGa1−xAs layers of DH diodes.

ISSN:0021-8979    

DOI:10.1063/1.1663570

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A confined random‐particle flux (such as photons in an electroluminescent diode, integrating sphere, or room, music or other phonons in an auditorium, gas molecules in an imperfect vacuum chamber, neutrons in a reactor, etc.) is analyzed, and simple expressions are shown to exist for the mean path length, transit time, surface transmissivity, projected area, absorption rate, etc., that arise in its description. The results are applied to a theoretical and experimental analysis of the coupling of photons from their source within an indirect‐band‐gap electroluminescent diode (or within a sufficiently transparent heterostructure direct‐band‐gap diode) into the ambient or into a multimode optical fiber. We find that about two‐thirds of the internally generated photons will reach air from an encapsulated rough‐sawed red‐emitting GaP(Zn,O) electroluminescent diode of reasonably high purity and contact reflectivity, whereas in a comparable green‐emitting GaP(N) diode only about one‐fourth of the photons escape while three‐fourths are absorbed within the diode bulk and at its contacts.

ISSN:0021-8979    

DOI:10.1063/1.1663571

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Silicon‐site distribution in GaAs under the influence of a second dopant was studied by measuring the Si localized vibrational modes and the carrier concentrations of a series of samples. Each sample had the same total Si concentration, [Si], but with different concentrations of a second dopant. Semiquantitative results give a relationship between [SiGa]/ [SiAs] and the concentration of the second dopant which is compared with a calculation based on the thermodynamically predicted Fermi‐level effect as formulated by Longini and Greene.

ISSN:0021-8979    

DOI:10.1063/1.1663572

出版商:AIP    

年代:1974

数据来源: AIP