摘要:

The capacity of a magnetically delayed vacuum switch to conduct current depends on the density of plasma injected into the switch. Exceeding the current capacity results in the switch entering a lossy mode of operation characterized by a transient interruption of the main current (opening behavior) and a rapid increase of voltage across the vacuum gap. Streak and framing photographs of the discharge indicate that a decrease of luminosity near the middle of the gap precedes the transition to the opening phase. The zone of low luminosity propagates toward the cathode. This evidence suggests that the mechanism causing the opening phase is erosion of the background plasma in a manner similar to that in a plasma‐opening switch. The resulting ion depletion forces a space‐charge‐limited conduction mode. The switch inductance maintains a high discharge current even during the space‐charge‐limited conduction phase, thus producing high internal fields. The high accelerating voltage, in turn, produces electron and ion beams that heat the electrode surfaces. As a result of the heating, jets of electrode vapor issue from the electrodes, either cathode or anode, depending on the selection of electrode materials.

ISSN:0021-8979    

DOI:10.1063/1.353196

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The results of a Monte Carlo model for calculating the trajectories of electrons in the plasma sheath region in reactive‐ion‐etching plasmas are described. The calculations illustrate how the oscillating movement of the sheath imparts energy to electrons and alters the electron energy distribution (EED) within the bulk of a 13.56 MHz Ar discharge. The study is limited to low‐pressure discharges of less than about 10 mTorr, where the effects of electron‐molecule collisions can be ignored. Under these conditions it is found that the sheath imparts energy preferentially to low‐energy electrons. Calculated EEDs for electrons striking the electrodes in a radio‐frequency reactor are also presented. Most electrons strike the electrodes with energies of a few eV, but some electrons strike the substrate surface with impact energies as high as 20 eV. This may be an important consideration when modeling etch mechanisms. Secondary electron emission caused by ion bombardment of the electrodes is also modeled. Simulated EEDs for secondary electrons that are produced at the electrodes and accelerated by the action of the sheath potential into the plasma region are presented. These electrons have energies of up to several hundred eV and are therefore important in plasma‐sustaining mechanisms.

ISSN:0021-8979    

DOI:10.1063/1.353197

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We prepared silica glasses having various concentrations of chlorine, fluorine, hydrogen (SiO2−x), and oxygen (SiO2+x) to examine the precursors of paramagnetic centers induced by &ggr; rays. In the case of glasses sintered under chlorine and hydrogen ambients, the concentration of theE’center induced by &ggr;‐ray irradiation scaled with the partial pressure of chlorine and hydrogen. In contrast, theE’center was suppressed in glasses doped with fluorine. Stress in the glasses was also found to enhance formation of theE’center. Planar ring structures in the glass are influenced by stress and are proposed as precursors to theE’center.

ISSN:0021-8979    

DOI:10.1063/1.353198

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The objective is to develop a quantitative model for simulating dislocation motion and multiplication in gallium arsenide (GaAs) crystals during growth from the melt by taking the crystallography of slip into account. A constitutive model that couples microscopic dislocation motion and multiplication to macroscopic plastic deformation is employed for developing the model. The density of dislocations in the crystal is predicted by assuming the crystal to be grown under quasi‐steady‐state conditions. The thermoelastic stresses are calculated from a two‐dimensional finite‐element analysis, and then transformed into the resolved shear stresses in each slip system for the simulation of dislocation motion and multiplication. A numerical example is presented to verify the validity of the model. The calculated distribution of dislocation density on (001) GaAs wafer shows fourfold symmetry which is consistent with etch pit observations made by Jordan, Caruso, and Von Neida [Bell Syst. Tech. J.59, 593 (1980)]. Although the emphasis is placed on GaAs, the model can be applied to other electronic and photonic materials.

ISSN:0021-8979    

DOI:10.1063/1.353199

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Thermal bleaching of silver halide photochromic glasses is studied by electron paramagnetic resonance spectroscopy of photoinduced CuIIcenters. During exposure to ultraviolet light, the only stable CuIIspecies is the (CuIIVAg)Acenter, which is a CuII‐silver vacancy complex with the vacancy in a nearest position. In the dark, this center rapidly decays via two parallel channels. The first involves the dissociation of the complex by displacement of the vacancy along a [110] direction, with an activation energyE3=0.44 eV and a frequency factork30=3.4×105s−1. The second channel involves the conversion of the (CuIIVAg)Acenter into a (CuIICl−VAg)Bcenter, where the silver vacancy is in the next nearest position along the [100] direction. This process occurs with an activation energyE1=0.44 eV and a frequency factork10=3.1×105s−1. The (CuIICl−VAg)Bcenter slowly decays by a vacancy hopping mechanism, with an activation energyE2=0.22 eV and a frequency factork20=4.6 s−1. To explain these two decay channels, it is proposed that the (CuIIVAg)Aand (CuIICl−VAg)Bcenters annihilate via the formation of a CuIion and a neutral complex (AgIIVAg)Awhich migrates to the surface of the silver halide particle, where electron‐hole recombination occurs.

ISSN:0021-8979    

DOI:10.1063/1.353200

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effect of MeV ion irradiation damage on the luminescence lifetime of erbium‐doped silica glass films has been studied. The 10‐&mgr;m‐thick films were first implanted with 3.5 MeV Er at a fluence of 5×1015cm−2. When optically pumped at 488 nm, the films show a clear photoluminescence spectrum centered around 1.535 &mgr;m, corresponding to the4I13/2→4I15/2transition of Er3+(4f11), with a luminescence lifetime of 5.5 ms. After thermal annealing at 900 °C, the lifetime increases to 14.1 ms. Radiation damage was then introduced in the annealed films using 1 MeV He, 3.5 MeV C, 5.5 MeV Si, or 8.5 MeV Ge ions. The lifetime is decreased by irradiation with fluences as low as 1011ions/cm2and continues to decrease with fluence until saturation occurs above ≊1014ions/cm2. The saturation lifetime is ion‐mass dependent and ranges from 6.6 to 8.5 ms. The lifetime changes are explained in terms of nonradiative energy transfer processes caused by irradiation‐induced defects in the silica. A model for lifetime changes as a function of ion fluence is derived, assuming an inverse relation between the nonradiative lifetime and the defect density. Fits to the data show that the defect generation rate is a sublinear function of the ion fluence. The ion damage effects are governed by the electronic component of the energy loss along the ion trajectories.

ISSN:0021-8979    

DOI:10.1063/1.353201

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Silicon is an amphoteric impurity of gallium arsenide that is present in different defect configurations. This work reports on the effects of heat treatment on defect reactions of heavily silicon‐doped gallium arsenide crystals. The distribution of segregation, lattice parameter, and electrical properties was studied for several heat treatments. When the crystals were bulk‐annealed at between 700 °C and 1000 °C for 20 h, zone‐distributed segregation was observed at the area with a silicon concentration of about 1×1019cm−3by etching and x‐ray topography. Regions observed to have silicon‐related segregation exhibited a decrease in lattice parameter when the crystals were annealed below 850 °C for 20 h then quenched. In addition, such regions exhibited little change in lattice parameter when the crystals were annealed above 850 °C. For electrical properties, the largest decrease in carrier concentration and mobility of such regions was observed when the crystals were annealed at 700 °C. This change in the characteristics of such regions seems to be affected not only by heavily doped silicon but also by excess arsenic.

ISSN:0021-8979    

DOI:10.1063/1.353202

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Dynamic activities of &agr;, &bgr;, and screw dislocations in a GaP crystal containing sulphur as the main impurity at a concentration of 7×1017cm−3are investigated as a function of stress and temperature by means of the etch pit technique. Generation of all types of dislocations from a surface scratch is found to be suppressed at temperatures higher than 500 °C and is interpreted in terms of dislocation locking due to impurities and/or impurity‐defect complexes as has been observed in GaAs and InP. &agr; dislocations move faster than &bgr; and screw dislocations and their velocities are expressed with the same type of empirical equation as a function of the stress and the temperature as those in other semiconductors. Roughly speaking, dislocations in GaP move at velocities lower than those in GaAs by about two orders of magnitude.

ISSN:0021-8979    

DOI:10.1063/1.353203

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Photoluminescence coupled with repetitive thermal annealing has been used to determine the diffusion coefficients for intermixing in InxGa1−xAs/GaAs quantum wells and to study the subsequent effects of ion implantation on the intermixing. It is shown that following ion implantation there is a very fast interdiffusion process, which is independent of the implanted ion and that is thought to be due to the rapid diffusion of interstitials created during the implantation. Following this rapid process, it was found that neither gallium nor krypton ions had any effect on the subsequent interdiffusion coefficient. Following arsenic implantation in addition to the initial damage related process, an enhanced region of interdiffusion was observed with a diffusion coefficient that was an order of magnitude greater than that of an unimplanted control wafer. This enhanced process is thought to be due to the creation of group III vacancies by the arsenic atoms moving onto group V lattice sites. This fast process was present until the structure had broadened by about 75 A˚ when the diffusion coefficient returned to the unimplanted control value. The activation energy for the interdiffusion was measured over the temperature range 1050–750°C and a value of 3.7±0.1 eV was measured. This was found to be independent of the implanted ion.

ISSN:0021-8979    

DOI:10.1063/1.353204

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The dielectric continuum model of longitudinal‐optical phonons in polar semiconductors is used to define the role of interface longitudinal‐optical phonons in affecting phonon‐assisted &Ggr;–Xtransitions in GaAs–AlAs and GaAs–GaP superlattices. In particular, the dielectric continuum model for interface optical phonons is used in conjunction with a Kronig–Penney model of the superlattice electronic properties for two purposes: to specify superlattice parameters where interface‐phonon‐assisted &Ggr;–Xtransitions are expected and to estimate relative transition probability amplitudes for interface‐phonon‐assisted &Ggr;–Xtransitions in selected short‐period superlattices.    

ISSN:0021-8979    

DOI:10.1063/1.354060

出版商:AIP    

年代:1993

数据来源: AIP