摘要:

DXcenters, deep levels associated with donors in III‐V semiconductors, have been extensively studied, not only because of their peculiar and interesting properties, but also because an understanding of the physics of these deep levels is necessary in order to determine the usefulness of III‐V semiconductors for heterojunction device structures. Much progress has been made in our understanding of the electrical and optical characteristics ofDXcenters as well as their effects on the behavior of various device structures through systematic studies in alloys of various composition and with applied hydrostatic pressure. It is now generally believed that theDXlevel is a state of the isolated substitutional donor atom. The variation of the transport properties and capture and emission kinetics of theDXlevel with the conduction‐band structure is now well understood. It has been found that the properties of the deep level when it is resonant with the conduction band, and is thus a metastable state, are similar to its characteristics when it is the stable state of the donor. And it has been consistently found that there is a large energy difference between the optical and thermal ionization energies, implying that this deep state is strongly coupled to the crystal lattice. The shifts in the emission kinetics due to the variation in the local environment of the donor atom suggest that the lattice relaxation involves the motion of an atom (the donor or a neighboring atom) from the group‐III lattice site toward the interstitial site. Total energy calculations show that such a configuration is stable provided that the donor traps two electrons, i.e., has negativeU. Verification of the charge state of the occupiedDXlevel is needed as well as direct evidence for its microscopic structure.

ISSN:0021-8979    

DOI:10.1063/1.345628

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Perturbation expansions and rigorous bounds on the effective conductivity tensor &sgr;eofd‐dimensional anisotropic two‐phase composite media of arbitrary topology have recently been shown by the authors to depend upon the set ofn‐point probability functionsS(i)1,...,S(i)n.S(i)ngives the probability of simultaneously findingnpoints in phasei(i=1,2). Here we describe a means of representing these statistical quantities for distributions of identical, oriented inclusions of arbitrary shape. Our results are applied by computing second‐order perturbation expansions and bounds for a certain distribution of oriented cylinders with a finite aspect ratio. We examine both cases of conducting cylindrical inclusions in an insulating matrix and of insulatingcracksorvoidsin a conducting matrix.

ISSN:0021-8979    

DOI:10.1063/1.345711

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper discusses the reliability of scanning tunneling microscopy (STM) images of mesoscopically rough surfaces. The specific structure of these images represents a convolution between the real surface topography and the shape of the tip. In order to interpret these images quantitatively, the line scans of steep and high steps can be used to obtain an image of the tip itself. This image shows tip radii ranging typically from 5 to 15 nm and cone angles of about 30° over a length of 80 nm, and can in turn be used to recognize the limits of STM resolution on a rough surface: High‐resolution transmission electron microscopy cross‐section images of Au island films on a Au‐Nb double layer are convoluted with the experimentally observed tip shape; the resulting line scans correspond very well with STM graphs of the same samples. Finally an overall criterion for the resolution of the STM on such surfaces is proposed.

ISSN:0021-8979    

DOI:10.1063/1.345712

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electrostatic problems of the configurations of two dielectric spheres are solved with the aid of the inversion transformation. The potentials due to a unit point charge located on the symmetry axis or that excited by a uniform external field are obtained. In the case of conducting spheres, our results are in agreement with the previous results obtained by the method of images.

ISSN:0021-8979    

DOI:10.1063/1.345713

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The phase‐angle method to measure electrical resistivity in nonmagnetic metals is calculated for samples presenting the hollow circular geometry. The phase angle versus the operating frequency for a general hollow circular cylinder geometry shows a similar qualitative behavior when compared with the massive cylinder geometry. A discussion of a procedure for a desirable experimental condition related to the geometrical parameters and exciting signal is presented. UFaipxr

ISSN:0021-8979    

DOI:10.1063/1.345714

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Fresnel diffraction theory is combined with a three‐dimensional temperature model to predict accurately the beam intensity profile produced by a steady‐state thermal lens in 250‐&mgr;m liquid films. In the comparison of theory and data, the optical parameters of the thermal lens instrument and the thermo‐optical properties of the sample were introduced into the model; it was not necessary to adjust any parameter in the theory to produce good agreement between the predicted and observed beam profile. Because no parameters are adjusted to match theory to data, the thermal lens measurement provides an absolute measurement of sample absorbance. The model is used to predict the behavior of the thermal lens in thin films with respect to sample absorbance, sample thickness, laser power, and optical alignment. The new model is compared with several models from the literature; it is necessary to utilize the three‐dimensional heat‐flow analysis and Fresnel diffraction theory to obtain an accurate description of the behavior of the thermal lens in measurements of thin films.

ISSN:0021-8979    

DOI:10.1063/1.346057

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Y‐cut LiNbO3single crystals have been implanted with 200‐keV Ti+at doses up to 4.0×1017Ti/cm2. The annealing behavior has been studied with implantations performed at 77, 300, and 620 K. The amorphous surface layers have been annealed at 1273 K in a wet oxygen atmosphere for 2 to 8 h to achieve epitaxial regrowth. Channeling and mode spectroscopy have been applied to investigate the regrowth process. Refractive index profiles have been calculated with an inverse WKB algorithm. A maximum increase of 0.040 for the extraordinary and 0.019 for the ordinary refractive index was found at He‐Ne wavelength (632.8 nm). This indicates a solubility limit of 3.3×1027/m3for Ti in LiNbO3. The annealing time to achieve perfect regrowth depends on the ion dose and irradiation temperature. Higher implantation temperatures yield dynamical annealing; thus, a shorter post‐implantation anneal is required.

ISSN:0021-8979    

DOI:10.1063/1.345715

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An all‐optical integrated optics beam‐scanning device is analyzed. It consists of a surface relief grating used to couple both a control and a signal beam into and out of a nonlinear planar waveguide, respectively. Varying the control beam power tunes the signal beam out‐coupling angle. Both local and diffusive nonlinearities are considered, and various design parameters are discussed. The theoretical results are compared to experimental data from ZnS waveguides for the thermal diffusive case.

ISSN:0021-8979    

DOI:10.1063/1.345716

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Steady‐state space‐charge fields generated by a pair of light interference patterns, each of them formed by a pair of optical plane waves, are studied. Analytic solutions of the steady‐state space‐charge fields in photorefractive crystals are derived for small laser intensity at large modulation depth. Numerical solutions for the photorefractive crystal Bi12SiO20(BSO) are also obtained by utilizing Powell’s method without the assumption of small laser intensity, and they are compared with the analytic solutions in both cases of stationary light interference patterns and moving light interference patterns. The intermode space‐charge fields, which may cause the second‐order cross‐talk problem in volume holographic interconnections, are described. The data regions are obtained in which the effect of intermode space‐charge fields are suppressed and the criteria for optimal implementation of volume holographic interconnections are satisfied.

ISSN:0021-8979    

DOI:10.1063/1.345717

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We measured the triplet extinction coefficients &egr;Tover the laser action spectral region of DODC, DMC, Sulforhodamine B, Rhodamine 575, Coumarin 523, Coumarin 521, Coumarin 504, Coumarin 498, Coumarin 490, LD466, bis‐MSB, and BBO. We employed the different lines from an argon‐ and a krypton‐ion cw laser for excitation. McClure’s method [J. Chem. Phys.19, 670 (1951)] was again employed to measure the triplet extinction coefficients. We provide a simplified derivation of McClure’s equation. The triplet extinction coefficient of Rhodamine 575 was also measured by using the depletion method and improving it by reconstructing for true triplet‐triplet (T‐T) absorption. The &egr;Tvalue obtained is in good agreement with the one obtained by McClure’s method.

ISSN:0021-8979    

DOI:10.1063/1.345718

出版商:AIP    

年代:1990

数据来源: AIP