摘要:

Device‐qualitya‐Si:H thin films, grown by rf magnetron sputtering, were annealed in the temperature range up to 850 °C and studied byinsituellipsometry, spectroscopic ellipsometry, and thermal evolution measurements. Annealing causes a volume reduction which can be as high as 5%, and after annealing atT≳800 °C the material becomes microcrystalline with an average crystallite size that depends on the annealing temperature. A detailed analysis of the peak height of the imaginary part of the pseudodielectric function ⟨&egr;(&ohgr;)⟩, combined with the examination of the fundamental gap, the average gap (Penn gap), and the refractive index ofa‐Si:H, provides new insight on the role of hydrogen and the structural modifications induced by thermal annealing. Based on the presented experimental findings we propose the following: (a) annealing belowTscauses reduction of the isolated microvoids; (b) the weakly bound hydrogen is correlated with regions with a high density of microvoids; and (c) the evolution of weakly bound hydrogen does not drastically influence the optical properties of the film while evolution of isolated hydrogen does. The rate of change of the optical properties as a function ofTis (a) nearly constant forTT<Ts, (b) increases forT≳Ts, and (c) decreases dramatically forT≳600 °C, therefore indicating irreversible structural changes atT≳Tsmainly due to isolated hydrogen loss.

ISSN:0021-8979    

DOI:10.1063/1.349341

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Novel photoconductive polyimides have been developed, whose monomer units are composed of a series of thiophenylene moieties, ‐C6H4S‐, and imide groups. The most photosensitive polyimide shows an excellent photosensitivity of less than 1.0 &mgr;J/cm2in the visible light region, 400–570 nm. These photosensitive polyimide films are prepared by polymerizing the cast prepolymer films and annealing at the melting points of the polyimides. In this process their photosensitivities remarkably increase with the increase of crystallinity. From the structural studies by ultraviolet visible absorption, x‐ray diffraction, infrared absorption, and x‐ray photoelectron spectroscopy measurements, it is proposed that the coplanary conformation takes place in the crystallizing. The overlapped &pgr; orbitals, perpendicular to the polymer chains, lead to the more expanded conjugate system.

ISSN:0021-8979    

DOI:10.1063/1.349342

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A phenomenonological model of topographic contrast in secondary electron microscopy is presented. This model involves exponential attenuation of isotropically generated secondary electrons. The effect of primary beam diameter and the material dependent secondary electron attenuation length on secondary electron images is demonstrated by explicitly computing linescans of images of straight surface steps. These computed linescans are directly compared with those obtained from monatomic surface steps on Si(100) imaged at normal incidence in an ultrahigh‐vacuum scanning transmission electron microscope. An asymmetry in the experimental linescan cannot be fit by any combination of model parameters suggesting that this contrast is not simply due to surface topography. A simple explanation for the contrast reversal observed in secondary electron images of surface steps when the primary beam changes direction from the upstairs to the downstairs direction is presented. The possibility of determining secondary electron emission parameters and extracting surface chemical and electronic information using high spatial resolution secondary and Auger electron imaging is briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.350350

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Intracavity laser absorption spectroscopy was used to measure the number density of neutral ground state barium atoms desorbed from an operating dispenser cathode. The measurement suggests an order of magnitude value of 108atoms/cm3at a distance of 5 cm from the emitting surface. This is the first direct state selective measurement of the barium density near to the surface of an operating cathode which can be directly traced to conventional multipass absorption spectroscopy. The value we obtain is consistent with results reported by other workers using less direct methods and allows more detailed statements to be made concerning the chemical state of the Ba at the instant of desorption.

ISSN:0021-8979    

DOI:10.1063/1.349343

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The oxidation kinetics of copper thin films have been studied at temperatures below 200 °C in air. The protection of copper from oxidation can be achieved by alloying copper film with Ti, Pd, Cr, or Al. The influence of the composition and microstructure to the oxidation rate has been studied. The compounds Cu3Ti, Cu3Pd, and CuAl2are stable in the oxidation ambient. The formation of Cr‐oxide, which is a passive oxide, explains the inhibition of oxidation on Cu‐Cr films. Compared with the crystalline phase, the amorphous Cu65Ti35alloy film is more oxidation resistant. A TiN layer with oxygen incorporated is more effective in preventing copper oxidation than a TiN layer without oxygen incorporated. A passivating Si3N4layer on copper thin films can prevent copper oxidation effectively at 350 °C in oxygen ambient.

ISSN:0021-8979    

DOI:10.1063/1.349344

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The oxidation kinetics of reactively sputtered amorphous Ta36Si14N50thin films are studied in dry and wet ambient in the temperature range of 650–850 °C by backscattering spectrometry, Dektak profilometer, and x‐ray diffraction analyses. The dry oxidation is well described by a parabolic time dependence which corresponds to a process controlled by the diffusion of the oxidant in the oxide. The growth of the oxide in wet ambient is initially very rapid and then proceeds linearly which means that the process is reaction limited. Both oxidation rates are thermally activated. The activation energies are 2.0 eV for dry and 1.4 eV for wet ambient. The pre‐exponential factors are 0.17×1016A˚2/min and 7.4×108A˚/min, respectively. Both the dry and wet oxidation of the amorphous ternary Ta36Si14N50film result in the formation of an x‐ray amorphous Ta14Si5.5O80layer.

ISSN:0021-8979    

DOI:10.1063/1.349345

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Adsorption of Ba and its effect on the GaAs(110) surface oxidation has been studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The Ba adsorption onto the surface results in a disordered interface of Ba and the GaAs surface at temperatures <500 °C. However, the reactivity of the GaAs surface to oxygen is dramatically enhanced by the adsorbed Ba atoms. This enhancement of the surface oxidation is proportional to the Ba exposure. Study of LEED and AES intensities has also revealed evidence of Ba‐induced surface disorder on the GaAs.

ISSN:0021-8979    

DOI:10.1063/1.349346

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have achieved phase‐locked operation of a module consisting of up to seven relativistic magnetrons. The magnetrons are connected by waveguide in a peer/peer configuration, with no one magnetron acting as a master oscillator. The signals used for coupling are each a substantial fraction of a magnetron’s radiated power. Total extracted power, at 2.8 GHz, was 2.0 GW with four magnetrons and 2.9 GW with seven. Several interconnection geometries were explored. One particular geometry was found to produce qualitatively better phase‐locked operation than any other. This was in agreement with the predictions of a numerical model of the magnetrons as coupled van der Pol oscillators.

ISSN:0021-8979    

DOI:10.1063/1.349347

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The switching behavior of ferroelectric capacitors experiencing arbitrary time‐dependent electric fields and arbitrary initial conditions is investigated both theoretically and experimentally. A general approach for modeling incomplete dipole switching in ferroelectric capacitors is used to derive equations describing the electrical behavior of a simple characterization circuit with arbitrary initial conditions and arbitrary time‐dependent applied voltages. The equations include four experimentally determined parameters: the remanent and spontaneous polarizations, the coercive field, and the ferroelectric dielectric constant. Once these model parameters are determined from a single high‐frequency sinusoidal hysteresis loop, model predictions are made with no adjustable parameters. The circuit behavior for both sinusoidal and trapezoidal input signals is computed, including asymmetric and nonperiodic signals as well as several different initial conditions. The accuracy of the model predictions is quantitatively verified with experimental data. The approach is also utilized to model the switching behavior of a ferroelectric capacitor containing a sheet of space charge. It is found that hysteresis loop distortions resulting from ionizing radiation resemble those caused by a sheet of space charge. This quantitative modeling capability facilitates the optimization of the design of ferroelectric memory circuits by minimizing the amount of required electrical testing and characterization. It can also be used to facilitate the identification and understanding of degradation mechanisms occurring in ferroelectric thin films.

ISSN:0021-8979    

DOI:10.1063/1.349348

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Novel field‐effect transistors (FETs) with unusual high‐power capabilities have been demonstrated previously. They are fabricated using the grown‐in metal‐semiconductor junctions of semiconductor‐metal eutectic composite materials. Here, computer modeling has been used to examine the relation between their exceptional resistance to avalanche breakdown and the effects of floating gate junctions between the gate and drain. Calculations are presented that show how composite geometry and materials parameters could be optimized to give extremely large off‐state blocking voltages combined with low series resistance. These transistors should, in principle, be capable of an on‐state power dissipation lower than that of any conventional high‐voltage FET device.

ISSN:0021-8979    

DOI:10.1063/1.349349

出版商:AIP    

年代:1991

数据来源: AIP