摘要:

The influence of different polishing methods on the atomic profiles obtained by direct ion implantation in semi‐insulating GaAs has been investigated, along with the effects of preimplantation etching. The results indicate that chem‐mechanical polishing technologies, contrary to chemical only polishes, produce residual damage that results in shallower and more sharply peaked profiles. Polishing related damage, however, may not bethefactor preventing a good electrical activation of implanted species. The acidity of the polishing fluid seems more important in determining the activation. Also, the dose implanted in uncapped, damaged wafers seems to be different, and generally lower, than the dose measured by the implanter.

ISSN:0021-8979    

DOI:10.1063/1.345451

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Radiation damage induced on a gallium arsenide surface by electron cyclotron resonance (ECR) plasma etching is studied. The number of displaced atoms (displaced atom density) formed by exposure to ECR plasma is determined quantitatively by Rutherford backscattering spectrometry aligned spectra. The density increases with increasing microwave power. The amount of increase of displaced atom density from the undamaged virgin surface &Dgr;Ddais 2.9×1015and 4.4×1015atoms/cm2at microwave power of 500 W (ion current density,Ii: 0.80 mA/cm2) and 800 W (Ii: 2.00 mA/cm2), respectively. The reflection high‐energy electron diffraction study shows that an amorphous layer is formed on the surface at 800 W (Ii: 2.00 mA/cm2). The effect of bias power and chamber pressure on the damage is also studied. The increase of damage (&Dgr;Dda: 3.2×1015atom/cm2) from ECR plasma etching with an rf bias of 15 W is less by a factor of 2 than damage of reactive ion etching (&Dgr;Dda: 6.9×1015atom/cm2) when compared at an ion current density of 1.17 mA/cm2. Low‐damage anisotropic etching can be achieved by ECR plasma etching.

ISSN:0021-8979    

DOI:10.1063/1.345452

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Calcium aluminate glasses melted in graphite crucibles were found to show photochromism. Upon exposure to ultraviolet radiation, broad absorptions with an apparent peak of around 2 eV and a shoulder around 3.5 eV were induced, and after interruption of the light illumination both bands faded at room temperature. A distinct photobleaching effect was observed in the fading process. Two kinds of electron‐paramagnetic‐resonance signals, one symmetric and the other asymmetric, were induced nearg=2 by exposure to radiation. The growing and fading behaviors of the symmetric and asymmetric components were parallel to those of the 2‐eV and 3.5‐eV band, respectively. It is strongly suggested that the photochromism originates from an electron trapped at the site of oxygen vacancy surrounded by Ca2+ions produced in graphite crucibles during melting under strongly reducing conditions.

ISSN:0021-8979    

DOI:10.1063/1.345453

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Modeling of rough step edges has been made and compared with scanning tunneling microscopy (STM) micrographs. In this paper, we use a phenomenological Hamiltonian to calculate diffraction profiles which can be used to determine the extent of step‐edge meandering. Comparison with experiment is made based on a parametrization of the step statistics obtained from STM data of silicon (001) step edges.

ISSN:0021-8979    

DOI:10.1063/1.345454

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A general Jones matrix representation for an arbitrary pretilt twisted nematic (TN) cell at any given applied voltage is obtained. A simplified Jones matrix representation for the high pretilt TN cell at the field‐off state is derived from this general Jones matrix representation. The validity of this simplified representation is examined by comparing the optical transmission of a high pretilt angle TN cell, at the field‐off state, as a function of the cell gap thickness obtained from this simplified representation with that obtained by the general representation. The result shows that the simplified Jones matrix representation for a TN cell at the field‐off state works very well even for the pretilt angle as high as 30°. In addition, a property of the average tilt angle of a TN cell is reported.

ISSN:0021-8979    

DOI:10.1063/1.345455

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Rapid thermal annealing of GaAs in an arsine ambient has been investigated. Uncapped 2‐in. GaAs wafers were annealed in an arsine‐N2gas mixture up to annealing temperatures of 1100 °C and annealing times of 10 s. No surface decomposition occurred at an arsine partial pressure of 12.5 Torr. This capless annealing technique was employed to the activation of shallow Mg implants in GaAs. The sheet resistance of the annealed layers as a function of the annealing temperature reveals a minimum at approximately 930 °C. At higher temperatures diffusion of Mg becomes significant. A part of the Mg accumulates at the GaAs surface and diffuses out. The Mg loss due to outdiffusion can be reduced using Si3N4cap layers. The internal diffusion of Mg at high temperatures depends on the arsenic pressure during the annealing.

ISSN:0021-8979    

DOI:10.1063/1.345456

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The generation and propagation of threading dislocations in GaAs grown on Si was studied by transmission electron microscopy. This study was conducted by analyzing dislocation structures in GaAs at various growth stages. The dislocation structure changes as the GaAs grows from initial islands to a thick film. These changes are explained by the following physical processes: (1) nucleation of dislocations in GaAs islands, (2) generation and propagation of threading dislocations during coalescence of initial GaAs islands and their subsequent growth, and (3) bending of threading dislocations under misfit‐strain force and their interactions. The second process results in threading dislocations extending from the interface to the surface in thin films. The third process causes an improvement in near‐surface quality in thick films. The iplication of this study in confining threading dislocations to near the interface is discussed.

ISSN:0021-8979    

DOI:10.1063/1.345457

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Jump distances of dislocations are determined from the spin‐lattice relaxation rates in a rotating frame [1/T1&rgr;] usinginsitunuclear magnetic resonance pulse techniques during creep of pure and doped NaCl single crystals. Effects of divalent impurity and solid solution are investigated by doping with Ca and LiCl, respectively. Compression creep tests were performed at 10–30 MPa at 473 K. Relaxation rates were evaluated from spin‐echo heights following &pgr;/2, locking, and 64° pulse sequence. The amplitude of the spin echo decreased as soon as the load was applied following which it increased until the steady‐state creep was reached, at which point a saturation value was observed. Mean jump distance of the mobile dislocations decreased with strain during the transient creep reaching a constant value at the onset and during the secondary creep. While the addition of 0.01 Ca has negligible influence on the jump distance, a solid solution with 0.01 LiCl resulted in about a four‐fold increase. The results are compared and correlated with various microstructural parameters.

ISSN:0021-8979    

DOI:10.1063/1.345461

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The modulation wavelength dependence of the surface‐wave velocity in Cu/Ni superlattices has been investigated using Brillouin scattering. It is the first compositionally modulated system to be studied by this technique and the first for which elastic properties have been determined by both ‘‘macroscopic’’ methods and Brillouin scattering. Contrary to the enhancements previously reported in the biaxial modulus and in the Young’s modulus, the modulus associated with the surface‐wave velocity shows no evidence of anomalous behavior.

ISSN:0021-8979    

DOI:10.1063/1.345462

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The present paper is concerned with coated‐fiber composites in which the fibers possess cylindrical orthotropy and may have an arbitrary orientation distribution. A micromechanics model is developed which predicts the effective thermal conductivity and estimates the local fields of such composites which may be subjected to uniform heat fluxes on its boundary. The micromechanics model is based on the Mori–Tanaka mean‐field concept [T. Mori and K. Tanaka, Acta Metall.21, 571 (1973)] and provides explicit expressions for the effective conductivity of the considered composite aggregate which is highly complicated. The analysis shows that special care is needed in formulating an effective theory of composites with constituents possessing curvilinear anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.345463

出版商:AIP    

年代:1990

数据来源: AIP