摘要:

In this paper, we have made a theoretical investigation of second harmonic generation from intensep‐polarized laser radiation in an inhomogeneous plasma. The fluid equations have been employed to obtain the nonlinear response of the plasma electrons. The power conversion efficiency of the generated second harmonic wave depends drastically on the scale length of the plasma inhomogeneity and the angle of incidence of the laser radiation with the density gradient of the plasma.

ISSN:0021-8979    

DOI:10.1063/1.335578

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The average values of the electron temperatureTeand the electron densityNein the corona plasmas of spherically irradiated high‐Ztargets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 &mgr;m) and the frequency‐tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15–200 A˚. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency‐tripled laser irradiation,Te=2600±600 eV andNe>6×1020cm−3. This is consistent with a ‘‘flux limit’’ smaller than 0.1. The estimated values ofTeandNeare lower in the corona plasmas produced using the fundamental (1.06 &mgr;m) irradiation.

ISSN:0021-8979    

DOI:10.1063/1.336288

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

During self‐break in spark‐gap switches, multiple streamers can form in close proximity to one another. The rate of expansion of these streamers is sufficiently fast that they can interact during the current pulse. To help understand how these closely spaced, expanding spark columns interact, a laser‐triggered spark gap has been studied in which two parallel columns (separation 1.3 mm) are simultaneously preionized, resulting in a pair of nearly identical, axisymmetric spark columns. The spark gap (electrode separation 1.2 cm) switches a 100 ns, 40–60 kV, 12‐20 kA, 1.5 &OHgr; waterline. Interferograms of the expanding arc channels are obtained with a laser interferometer having a time and spatial resolution of 5 ns and 10 &mgr;m, respectively. Voltage and current were measured with an internal capacitive‐voltage divider and a current viewing resistor. The interferograms show that for initially identical axisymmetric columns, the individual channels do not merge into a single larger axisymmetric spark column. Instead, regions of high gas density remain inside the combined column long into the recovery period. The columns also do not remain axisymmetric as they grow, indicating a long‐range interaction between the channels. The voltage drop and resistance of the dual channel spark gaps changes by less than 15% from that of a single spark channel. A scaling model is presented to explain the resistance measurements and to predict the change in resistance for multichannel spark gaps.

ISSN:0021-8979    

DOI:10.1063/1.335579

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The energy and angular distribution of ions striking the electrodes in rf discharges are of interest with respect to the application of such discharges to the processing of semiconductor materials. The ability to fabricate small (< 1 &mgr;m) semiconductor features using the plasma etching process results, in part, from the energetic and anisotropic flux of ions which strike the semiconductor surface. In this paper the energy and angular distribution of ions striking the electrodes in low‐pressure capacitively coupled rf discharges are studied using a Monte Carlo model for ion trajectories and a parametric model for the time‐dependent electric field within the sheath. Energy and angular distributions are discussed as a function of rf frequency, ion mass, and the mean‐free path between charge exchange collisions within the sheath. The ion energy distribution is found to be characterized by a scaling parameter proportional to (rf frequency × sheath thickness)2 × ion mass/(sheath voltage); small values of this parameter yield bimodal distributions, intermediate values yield distributions peaked at the maximum sheath potential, and high values yield distributions peaked at the average sheath potential. The ion energy distribution is also examined for different values of the dc and rf components of the sheath potential and for different models for the electric field within the sheaths. When the dc component of the sheath potential is small compared to the rf amplitude, a large thermal component to the ion energy distribution results. The implication of this result and that for the angular distribution of ions incident on the electrodes is discussed with respect to the isotropy of the etch obtained during plasma etching of semiconductor materials.

ISSN:0021-8979    

DOI:10.1063/1.335580

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The effect of ion trapping in the emitter sheath in ignited thermionic converters is studied. The ion trapping prevents the emitter‐sheath barrier from being higher than approximately 0.1 eV, when the current decreases in the converter. This gives a condition for the constriction of the arc.I‐Vcurves are calculated for an ignited thermionic converter with a hydrodynamic plasma theory that takes into account the effect of Coulomb scattering and volume recombination, but assumes that the electron temperature is constant in the plasma.

ISSN:0021-8979    

DOI:10.1063/1.335581

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Polycrystalline silicon diffusion sources have been analyzed using secondary ion mass spectrometry. Polysilicon films were grown by standard low‐pressure chemical vapor deposition and doped with As, P, or B by ion implantation. Although dopant segregation at the poly‐Si/single‐crystal‐silicon interface occurred and has been analyzed quantitatively, no diffusion barrier has been observed at this interface. Diffusion profiles in the single‐crystal substrate have been measured for diffusion temperatures between 800 and 1000 °C. It is shown by comparison to numerical simulations that these profiles obey standard diffusion theory. Proper boundary conditions to be used for such calculations are deduced for the different dopant species. Furthermore, the saturation concentration of boron in silicon over the temperature range given above has been reliably determined.

ISSN:0021-8979    

DOI:10.1063/1.335582

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Molybdenum disilicide films have been formed by a reaction of Mo with polycrystalline silicon. Implantation of phosphorus or arsenic prior to reaction has been shown to have a large effect on the silicidation process. The object of implantation was to enhance the silicide reaction by creating damage at the metal‐silicon interface. This, then, results in silicide films with less surface roughness (and a lower electrical resistivity). Molecular P+2ions were found to be more effective in creating damage than single P+ions, due to the fact that for P+2ions two simultaneous collision cascades occur which overlap. Apart from the beneficial effect of implantation damage, the introduction of phosphorus has a deleterious effect on the properties of the silicide films. This phenomenon is explained by the presence of a thin and nonuniform native oxide layer which hinders the silicide reaction. Without addition of phosphorus, new nuclei for the silicide reaction can be formed due to stress introduced by the formation of the silicide, which will act upon the oxide and cause it to break up at some weak spot. The effect of phosphorus is proposed to be that it renders the oxide more viscous which prevents this process from taking place. The x‐ray diffraction spectra revealed that the orientation of the grains in the polycrystalline MoSi2films is influenced by the method of preparation.

ISSN:0021-8979    

DOI:10.1063/1.335583

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Transmission electron microscope studies of carbon‐doped Czochralski silicon, when combined with previous infrared data on the same specimens, reveal a double peak in the carbon‐sited oxygen‐cluster size distribution after 64 h at 750 °C. The first peak, which represents most of the carbon and oxygen in the specimen, is comprised of clusters with an average of two oxygens per carbon atom. These clusters can survive 64 h at 1000 °C although they are not created by such an anneal, suggesting that carbon atoms have difficulty trapping a first oxygen atom at 1000 °C. The second peak in the distribution near 104oxygen atoms in size is populated with regular {111}‐octahedral precipitates having large dilatational strain fields. The two peaks in the size distribution, and their dependences on heat treatment, indicate roles for both seeding (creation of metastable clusters below critical size) and nucleation (achievement of energetic stability) in the formation of carbon‐sited precipitates. The observations confirm a trend toward octahedral precipitate morphologies in carbon‐doped specimens. However, the trend may result not from site differences but from effects of carbon or point defects on strain energy during precritical cluster growth. Finally, differences between secondary defects associated with precipitation in low‐ and high‐carbon specimens suggest that substitutional carbon atoms at 1000 °C act as sites for silicon self‐interstitial condensation near precipitates.

ISSN:0021-8979    

DOI:10.1063/1.335584

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This paper reports the results of lattice parameter measurements on the ternary semiconductor alloy Zn1−xMnxSe over the range 0≤x≤0.57. We find that the mean cation‐cation distance increases linearly with manganese concentrationxaccording to Vegard’s Law. It is also noted that this linear dependence occurs across the region in which the alloy changes crystal structure from zinc blende (x≤0.30) to wurtzite (0.33≤x). These observations are compared with the behavior of the crystal lattice as a function of composition in other AII1−xMnxBVIalloys. A fairly unifed pattern of behavior emerges, relating the lattice parameters and bond lengths for the entire family of these materials. In addition, this analysis provides an experimentally determined value of the tetrahedral radius of manganese.

ISSN:0021-8979    

DOI:10.1063/1.335585

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Ion beam mixing of layered iron‐boron films with 200‐keV Ar ions is investigated by x‐ray diffraction, Auger depth profiling, and high‐temperature resistivity. Samples consisting of alternating layers of electron beam deposited polycrystalline iron (25 nm thick) and boron (50 nm thick) were irradiated to doses from 5×1015to 1×1016ions/cm2, at rates ranging from 0.3 to 3.3 &mgr;A cm2. The mixing extends to a depth of 150 nm and increases with dose rate. This dependence is due to beam heating of the sample. The structure of the mixed material is amorphous iron boron.

ISSN:0021-8979    

DOI:10.1063/1.335586

出版商:AIP    

年代:1985

数据来源: AIP