摘要:

The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 &mgr;m long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic and optical devices. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359026

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In the spiral line induction accelerator, an intense electron beam is transported along an open‐ended beam pipe that makes multiple passes through the accelerating cavities. In the straight sections of the beam line, solenoidal focusing is used; in the bends, anl=2 stellarator field is used. At the solenoid/stellarator transition, where the beam equilibrium changes, a mismatch can occur, exciting oscillations of the beam envelope. Numerical simulation is used to show that the frequency, damping rate, and emittance growth associated with these oscillations are sensitive to nonlinear space‐charge forces that depend significantly on the radial profile of the beam. Comparisons between simulation and experimental results illustrate this sensitivity. It is shown that mismatch oscillations can be avoided by using a single thick quadrupole lens at the solenoid/stellarator transition. Simulation and experimental results show excellent agreement.

ISSN:0021-8979    

DOI:10.1063/1.359027

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Mn:Sr5(VO4)3F has been investigated as a laser material for operation near 1200 nm. Absorption and emission spectra are consistent with Mn5+substitution into the distorted tetrahedral V5+sites of this apatite crystal. Emission is almost entirely from the1Estate, resulting in a room‐temperature fluorescence lifetime of 475 &mgr;s. Together with a peak stimulated emission cross section of about 1×10−19cm2and strong, broad absorption bands, this is attractive for lamp‐ or diode‐pumped laser operation. However, the1Eemission makes Mn:Sr5(VO4)3F a three‐level system. Laser operation has been demonstrated at room temperature, but the efficiency is lower than expected. Single‐pass gain measurements and saturable absorption and fluorescence data indicate that the primary difficulty is excited‐state absorption at the pump wavelength. This absorption is very broad, and is probably due to1T1and1T2excited states. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359585

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on optical waveguide structures containing a thin liquid crystal (LC) film held between two photochromic command surfaces. The command surfaces consist of three monomolecular layers of a polymer with azobenzene side chains deposited according to the Langmuir–Blodgett–Kuhn technique. When exposed to light of appropriate wavelength, the command surfaces undergo atrans↔cisphotoisomerization process that induces a reversible change in the liquid crystalline orientation. Such an orientation change of the LC alters the optical properties of the optical waveguide. We present experiments on the dynamics of the LC orientation process. The transition is shown to be continuous, with the degree of orientation dependent on the ratio of thecis‐transchromophore concentration ratio in the command surface. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359028

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Concentration and effective temperature of carriers are established to compete in their influences on the band‐edge dielectric function of an active semiconductor medium under the lasing conditions. This competition is shown as capable of suppressing the relaxation oscillations and wavelength chirping in the modulation response of a semiconductor laser, provided the carrier injection and carrier heating are combined in a suitable way. The problem of how to combine them is studied under the small‐signal approximation assuming that modulation signal can be imposed on both the injection current and energy flux flowing into the active layer. All the numerical results relate to single‐frequency 1.55 &mgr;m GaInAsP/InP laser. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359029

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thermal diffusivity and conductivity of ceramic materials in a system of Si3N4‐SiO2‐Al2O3‐AlN composed of &agr; and &bgr; SiAlON (which is well known as duophase SiAlON ceramics) are investigated. Single‐phase &bgr;‐SiAlON ceramic has a thermal conductivity of 12.44 W/m K. The thermal conductivities of SiAlON ceramics decrease linearly with increasing content of &agr; phase and can be best described by the following equation:K=12.46–0.043f, wherefis the weight percentage of &agr;‐SiAlON content andKis the thermal conductivity of SiAlON ceramics. The thermal conductivity of single‐phase &agr;‐SiAlON was then estimated to be ∼8.16 W/m K, which is in excellent agreement with the literature reported values, ∼8.4 W/m K. This estimation is also close to the value, 8.22 W/m K, obtained by using Bruggeman’s variable dispersion theory. The temperature dependence of the thermal conductivity of duophase SiAlON ceramics varies with &agr; and &bgr; phase contents in the materials. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359030

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ultraviolet‐adsorption spectroscopy has been used to examine how the chamber wall affects the concentration of gas‐phase reactants in high‐density etching plasmas. This technique was employed to detect CF2in an inductively coupled discharge used for the selective etching of silicon dioxide relative to silicon nitride and polycrystalline silicon (polysilicon) films. In plasmas containing C2F6and CF4, the concentration of CF2depends strongly on the applied power and operating pressure as well as the amount of polymer on the walls of the chamber. Changes in the conditioning of the chamber during the etch process cause significant variations in the concentration of CF2in the discharge. The selectivity of etching SiO2relative to Si3N4films closely follows the concentration of CF2under a variety of plasma operating conditions. The ability to measure a fundamental plasma characteristic that reflects the level of conditioning of the chamber is an important step in the real‐time monitoring of a reactor parameter that currently can only be determined from postprocess measurements. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359031

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The detection of atomic O by two‐photon‐allowed laser‐induced fluorescence is implemented to obtain the spatial distribution and the temporal evolution of oxygen atoms in a 10 MHz parallel‐plate rf discharge. Absolute concentrations are determined via a titration technique for intensities typically found in 20–100 W, 0.1–3 Torr O2discharges, and are in the range 4–30×1014atoms/cm3. The spatial O distribution after initial turn on of the discharge is rather uniform, indicative of a uniform production of O atoms throughout the interelectrode space. Furthermore, the decay of the O concentration reveals information about the reaction of O atoms with surface materials in the plasma environment, while the rise of the population indicates a time‐dependent production rate. The dependence of the O‐concentration rise and decay rates on discharge pressure, power, and gas composition is explored. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359032

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effect of oxygen on the electrical and optical properties of In0.5Ga0.5P epitaxial layers grown on (100) GaAs by liquid‐phase epitaxy has been investigated by adding Ga2O3to the growth melt. As the amount of Ga2O3increases, the carrier concentration at 300 K decreases from 4×1016to 4×1015cm−3and the Hall mobility at 77 K increases from 2400 to 4000 cm2/V s. The photoluminescence at 17 K shows that the peak intensity of an extrinsic transition in the In0.5Ga0.5P layer is reduced when Ga2O3is added to the growth melt. These facts indicate that the main effect of Ga2O3is the reduction of impurity concentration in the growth melt. In the In0.5Ga0.5P layer grown from the Ga2O3‐added growth melt, the same deep trap, with an activation energy of 0.29 eV, as in an undoped layer is observed but the trap density is decreased. This implies that the deep trap is not due to a simple intrinsic defect, but related to an impurity. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359033

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Time‐resolved hot‐stage transmission optical microscopy is used to characterize the nucleation and growth kinetics of amorphous GeTe thin‐film crystallization. This technique provides experimental measurements of the fraction crystallized, the number of crystallites, and the crystallite size as a function of annealing time and temperature. The fraction‐crystallized data are modelled using the Johnson–Mehl–Avrami formalism to give an Avrami exponent of 4, consistent with previous measurements via time‐resolved reflection/transmission methods. Microstructural measurements provide sufficient data to deconvolute the individual contributions of nucleation and growth to this exponent. This work shows that crystallization of these films proceeds by nucleation at an increasing rate due to transient effects with isotropic two‐dimensional growth in the film plane. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359034

出版商:AIP    

年代:1995

数据来源: AIP