摘要:

High diffracted power and bandwidth in acousto‐optic guided wave Bragg cell are critically dependent on the interaction efficiency between the surface optic and acoustic waves. Through the overlapping integral, diffraction efficiency depends dramatically on the acoustic and optic field shapes in the crystal, and the surface acoustic wave penetration depth is strongly dependent on the frequency; thus, either the interaction efficiency and the acousto‐optic bandwidth are strictly related to the guide geometry. For these reasons the technological process to build an optical slab guide plays a critical role in fulfilling the desired characteristics of the Bragg cell; it determines the optical field shape in the crystal and, thus, the overall limitation of the cell. In the present work, a method to analyze the technological process role for the lithium niobate Ti diffused guide is presented for a collinear guided wave Bragg cell.

ISSN:0021-8979    

DOI:10.1063/1.337581

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Thin films ofa‐Ge:H with hydrogen contents ranging from 0 to 13 at. % prepared by the glow‐discharge process have been studied by spectroscopic ellipsometry. The resulting ellipsometric parameters have been analyzed by using standardn‐layer models, least‐squares regression analysis, and the Bruggeman effective media approximation theory. The results of the analyses show that the atomic percentage of hydrogen, in the amorphous binary alloy of Ge and H, can be represented by a void volume fraction in an effective medium approximation. These results are compared with those of infrared absorption spectroscopy. A good correlation between the percentage void determined from ellipsometry and the H content measured in thesea‐Ge:H films is found.

ISSN:0021-8979    

DOI:10.1063/1.337582

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Asymmetry introduced to an otherwise planar phased array Bragg cell transducer design results in the elimination of one of two steering acoustic wave fronts. Therefore, all of the acoustic power is applied to the acousto‐optic interaction process. In addition, a factor of 1.8 improvement in wide‐band acousto‐optic Bragg cell interaction efficiency is realized over the planar phased array design. The technique to establish the asymmetry was to use a periodic silver film as a quarter‐wave step. This new technique is particularly suitable for the construction of wideband Bragg cells at microwave frequencies.

ISSN:0021-8979    

DOI:10.1063/1.337583

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Photoluminescence studies have been performed on undoped and silicon‐doped GaAs crystals, which were annealed between 650 and 1000 °C under different arsenic pressures. Samples were also heat treated with the addition of pure elemental Ga, Mn, or Cu. Spectra were taken in the energy range 1.15–1.55 eV at the surfaces of the annealed crystals and at various depths below the surface. Newly observed zero‐phonon emissions at 1.31 and 1.347 eV are concluded to be related to CuGa‐(VAs)2and CuGa‐VAs, respectively. An emission at 1.467 eV also was found to be related to a CuGa‐containing complex. A new emission at 1.342 eV was found to be related to a fast diffusing MnGa‐containing complex. Most likely, the emission originates from a MnAscenter. The nature of these defects is discussed on the basis of their emission characteristics, diffusion behavior, and dependence on annealing parameters. Through this study it appeared that arsenic vacancies play a crucial role both in the establishment of defect equilibria and in the formation of complexes with MnGaand CuGa. A new luminescence peak at 1.448 eV was found to be related to theVAsdefect. Most probably, it has to be associated with the GaAsantisite. The presence of arsenic vacancies also induces a shift of the 1.492‐eV emission to 1.484 eV. This shift is attributed to the replacement of CAsby SiAsacceptors. Some evidence was found that a peak at 1.38 eV is associated withVGa. It is concluded that solid‐state equilibrium of native defects and impurities is only established at the surfaces but not in the bulk of the crystal during the heat treatments.

ISSN:0021-8979    

DOI:10.1063/1.337584

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A time‐of‐flight (TOF) study of the particles leaving a CuCl target after irradiation by 15 ns laser pulses at 308 nm is performed. It is shown that the ejected species are Cl, Cu, CuCl, Cu2Cl, Cu2Cl2, and Cu3Cl3. The majority of the products consists of CuCl. The TOF spectra can be fitted by the sum of two contributions: a Maxwell–Boltzmann (MB) and a Gaussian‐type (G) distribution. The MB distribution has a temperature ofT=6000 K for all masses. The average energy and the standard deviation in the energy of the G contributions are typical for every individual product. The results strongly suggest that the MB contribution is due to a single photon‐induced process, whereas the G contribution originates from a multiphoton and/or a multistep process.

ISSN:0021-8979    

DOI:10.1063/1.337585

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Thermal desorption methods have been used to investigate the interaction of propylene (C3H6) with Si(100)‐(2×1). The adsorption characteristics depend strongly on the availability of active sites at the Si(100) surface. Reactivity is enhanced byproductionof active sites during ion prebombardment. Adsorption of C3H6to a disordered, ion‐bombarded Si(100) surface results in nearly complete dissociation of C3H6for ion fluences as small as 1015Ar+ions/cm2. In contrast, for a thermally annealed and ordered Si(100) surface, only 65% of the C3H6dissociates. The remainder of the propylene chemically bonds to the surface as an undissociated molecule which desorbs intact at 550 K. The increase in reactivity is due to an increase in dissociative chemisorption which occurs at defect sites produced by ion bombardment. Reactivity is suppressed bycappingof active sites using atomic hydrogen preadsorption. Hydrogen passivates the Si(100) surface by occupation of silicon dangling bonds, which prevents adsorption of C3H6. By controlling the number and kind of active surface sites in this way, it is possible to manipulate the reactive ability of the Si(100) surface.

ISSN:0021-8979    

DOI:10.1063/1.337586

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present new experimental results in the photoresponse behavior of GaAs‐AlAs‐GaAs heterostructures. Structures consisted of a layer of AlAs several thousand angstroms thick, sandwiched between layers of GaAs which were several microns thick. The layer of GaAs nearest the surface was doped degeneratelyntype, whereas, the layer beneath the AlAs was doped nondegeneratelyntype. The asymmetric doping and the AlAs layer are shown to play an important role in determining the photoresponse. We present photocurrent per incident photo data, as a function of incident light energy, at a variety of external biases. We also present current‐voltage curves taken while samples were illuminated by an incandescent lamp. Zero bias photocurrent consistent with electron transport from the nondegenerate region beneath the AlAs to the degenerate region forming the surface is observed. As negative voltage is applied to the top of the sample, this photocurrent changes sign. These results are explained by introducing the concept of a ‘‘collecting interface’’ to account for fields and scattering in the AlAs. Further, we explain why the shape of the photocurrent spectrum depends upon the sign of the photocurrent.

ISSN:0021-8979    

DOI:10.1063/1.337587

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The effects of emitter‐base junction gradation, mobility gradients, and electric field gradients on the injected minority‐carrier density distributions in the base region of narrow‐base transistors are analyzed. It is shown that the collector current of transistors having a graded emitter‐base junction deviates from the ideal characteristics. The factors which contribute to this departure are analyzed in this paper. It is also shown that the emitter‐base forward bias voltage affects the transit time significantly in narrow‐base transistors, even when high injection level conditions are absent.

ISSN:0021-8979    

DOI:10.1063/1.337588

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Stress compensated quartz resonators having ultralinear frequency‐temperature responses have been discovered, consisting of doubly rotated cuts whose orientations, defined in terms of the polar angles &fgr; and &thgr;, lie on a locus where the second‐order temperature coefficients of frequency are zero in the range of &fgr;=10 °±2 ° and &thgr;=110 °±5 °. These angles of orientation are in close proximity to, or on the locus of, zero frequency coefficients of stress and are thus referred to as new linear and stress compensated (NLSC) cuts. In the vicinity of the NLSC cuts, a relatively strong 123¯1 x‐ray plane exists at &fgr; equal to 10.9 ° and &thgr; equal to +106.6 °. This x‐ray plane makes the manufacture of NLSC cuts easier and cheaper than ones previously reported. In this paper the theoretical and experimental values of the frequency‐temperature responses and some physical features of NLSC cuts are discussed.

ISSN:0021-8979    

DOI:10.1063/1.337589

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Nuclear magnetic resonance imaging using81Br is used to obtain measurements of an inhomogeneous temperature distribution in KBr. Possible applications of the technique are presented.

ISSN:0021-8979    

DOI:10.1063/1.337538

出版商:AIP    

年代:1986

数据来源: AIP