摘要:

The process of impurity‐induced layer disordering (IILD) or layer intermixing, in AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs) and superlattices (SLs), and in related III‐V quantum well heterostructures, has developed extensively and is reviewed. A large variety of experimental data on IILD are discussed and provide newer information and further perspective on crystal self‐diffusion, impurity diffusion, and also the important defect mechanisms that control diffusion in AlxGa1−xAs‐GaAs, and in related III‐V semiconductors. Based on the behavior of Column III vacancies and Column III interstitials, models for the crystal self‐diffusion and impurity diffusion that describe IILD are reviewed and discussed. Because impurity‐induced layer disordering has proved to be an important method for III‐V quantum well heterostructure device fabrication, we also review the application of IILD to several different laser diode structures, as well as to passive waveguides. We mention that it may be possible to realize even more advanced device structures using IILD, for example, quantum well wires or quantum well boxes. These will require an even greater understanding of the mechanisms (crystal processes) that control IILD, as well as require more refined methods of pattern definition, masking procedures, and crystal processing.

ISSN:0021-8979    

DOI:10.1063/1.341981

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have observed Hanle signals andn=0,p=1 parametric resonances of 23S1metastable helium atoms in a discharge cell by optically pumping the helium atoms with a tunable Nd:LNA laser. These resonances were used to construct a sensitive magnetometer for the measurement of very small magnetic fields. Since magnetometer sensitivity is proportional to the slope of the parametric resonance signal (signal amplitude divided by linewidth), the slopes for single‐line laser pumping were compared with similar quantities obtained from conventional helium lamp pumping. Laser pumping yielded 45 times greater slopes with comparable power requirements, thus establishing the potential for developing ultrasensitive resonance magnetometers using single‐line laser pumping.

ISSN:0021-8979    

DOI:10.1063/1.342042

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The small signal gain is calculated for a metal grating free‐electron laser consisting of a planar metallic grating and an opposing planar metal boundary. The TM01mode of the metal grating waveguide interacts with a cold, dense, mildly relativistic electron beam which is constrained to move along the axis of the waveguide. Since the interaction fields evanesce away from the slow wave supporting structure, a beam‐grating gap is included in the analysis. Results indicate appreciable gain at lower mm wavelengths over a 30‐cm interaction length at electron accelerating voltages as low as 20 kV. Interaction between the forward wave region of then=0 space harmonic and the electron beam slow‐space‐charge wave could result in output wavelengths as low as 400‐&mgr;m at 250‐kV accelerating voltages.

ISSN:0021-8979    

DOI:10.1063/1.342043

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The current multiplication observed when a relativistic electron beam is propagated in an initially neutral gas at subTorr pressures (0.1–0.3 Torr) is generally attributed to the two‐stream instability. A general expression for this current gain is derived for a scattered beam propagating in a neutral gas, which takes into account a quasihydrodynamic expression for the beam energy loss. Moreover, the beam‐to‐plasma density ratio is obtained as a function of time for a given beam pulse by numerically solving the electron energy and continuity equations. It is found that at a given beam‐to‐plasma density ratio, the current gain increases with increasing the beam energy, with the increase being most rapid for the small scattering angles. A finite average scattering angle is seen to reduce the current multiplication. The experimentally observed peak current gains are in good agreement with the predicted peak gains obtained by taking into account the time‐evolved beam‐to‐plasma density ratio.

ISSN:0021-8979    

DOI:10.1063/1.342044

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The effects of tension and compression applied to unbonded InGaAsP semiconductor diode lasers have been studied. The observed dependence of threshold, wavelength, and polarization of the laser output on the applied stress is explained in terms of the strain dependence of the valence‐band wave functions. The polarization behavior is found to be related to thermal stress and the structure of the device. A technique has been developed to measure the thermal stress induced by current heating at the 105‐dyn/cm2level.

ISSN:0021-8979    

DOI:10.1063/1.342045

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

This work describes a method to calculate the heating that occurs when a Gaussian laser beam is scanned across the surface of a flat object which may be coated with one or more layers of differing materials. The laser beam is characterized by its power, radius, and scan velocity. Each layer of the object is characterized by its thickness, density, heat capacity, and thermal conductivity. Absorption of laser light is assumed to vary linearly across any one layer, and this absorption is characterized by two dimensionless constants. Temperature rise versus time is calculated as a function of position within the multilayer stack. Use of the technique is illustrated by considering the case of an optically opaque organic dye/polymeric binder coated onto a polymeric substrate. Such a construction may be used in optical data storage applications.

ISSN:0021-8979    

DOI:10.1063/1.342046

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

During the conduction phase of the plasma erosion opening switch (PEOS), magnetic field has been observed experimentally to penetrate completely through plasmas up to 30 cm long. Current channels in the main body of the plasma have been observed that are more than 10 cm (or more than about 60 collisionless skin depths) wide. In addition, the maximum current carried by the switch before opening (the conduction current) seems to scale roughly linearly with plasma densitynand switch lengthl. Collisionlesspiccode simulations of the plasma switch show current conducted in skin‐depth‐like channels, with the conduction current scaling close tol 2/5andn1/4. In this paper, the effect of collisions on the behavior of the PEOS is investigated and is shown to bring thepicsimulations and experimental results in closer agreement. In collisional simulations, current channels as wide as those in experiments are observed, and the conduction current scales linearly withland asn1/2in the anode‐dominated case. In the cathode‐dominated case, linear scaling with both length and density can be inferred from the cathode penetration distance versus time.

ISSN:0021-8979    

DOI:10.1063/1.342050

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Using an electro‐optical method, we have determined the director tilt angle, the layer‐tilt angle, and the quiescent‐state azimuthal angles of a surface‐stabilized ferroelectric liquid‐crystal (SSFLC) cell as a function of temperature in the smecticCphase. The method is based on a collective switching of the director’s conical motion due to the interaction of the external field with the spontaneous polarization and the dielectric anisotropy of the liquid‐crystal medium, together with a one‐elastic constant free‐energy model. Using the equation of total free energy, we have proved that only splayed states could be stabilized in layer‐tilted geometry, but bistable cells could still be obtained. When the surface interactions at both substrate surfaces are nonidentical, the SSFLC cell will exhibit two distinct quiescent states: one stable and the other quasistable. The twist angles of the director from top to bottom substrates at quiescent states and the ratio of the surface polar to nonpolar interaction are deduced. The experimental observation and calculation on an overshoot in the rising part of the optical response upon bipolar switching are also presented.

ISSN:0021-8979    

DOI:10.1063/1.342019

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The role of magnesium as ap‐type dopant in the growth of InP by molecular‐beam epitaxy (MBE) has been investigated. The growth was performed at substrate temperatures of ≊500 °C under conditions which produced high‐quality unintentionally doped InP with 77 K residual electron concentrations ofND−NA≊2×1015cm−3and mobilities up to 42 500 cm2 V−1 s−1. InP grown in an elemental Mg flux under such ‘‘optimum’’ conditions has electrical properties which are comparable to those of the undoped material. Using low‐temperature photoluminescence, the presence of electrically active shallow acceptors due to Mg and C has been detected in the ‘‘Mg‐doped’’ samples, with Mg being the dominant impurity. Mg is also found to be the principal, electrically active shallow acceptor in undoped InP. The activation energies for Mg and C are 40.9 and 44.4±0.3 meV, respectively, in excellent agreement with previously published data for low‐dose ion‐implanted InP. Secondary electron microscopy studies on the Mg‐doped InP show that the concentration of morphological defects increases as the Mg flux is increased, suggesting Mg is responsible for assisting the formation of defects. However, the increase in defect density does not appear to affect either the electrical or the optical properties of the semiconductor. The small concentration of Mg incorporated into InP from an elemental source makes it unsuitable as ap‐type dopant in MBE growth under the condition discussed here.

ISSN:0021-8979    

DOI:10.1063/1.342020

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Properties of diamondlike coatings deposited in a modified design of the plasma reactor system are reported. Benzene and monosubstituted benzenes are used as the source gases. The films have been analyzed using scanning electron microscopy, glancing angle x‐ray diffraction, Fourier transform infrared spectroscopy, and x‐ray photoelectron spectroscopy techniques. Large crystallites (∼30 &mgr;m) are observed. The x‐ray diffraction and x‐ray photoelectron spectroscopy have been utilized to identify the physicochemical nature of the deposited films. Fourier transform infrared spectroscopy results suggestsp3type of bonding in the films. Films are colorless, electrically insulating (≥109&OHgr; cm), and corrosion resistant.

ISSN:0021-8979    

DOI:10.1063/1.342021

出版商:AIP    

年代:1988

数据来源: AIP