摘要:

Properties of tantalum silicide (TaSix) films deposited from a TaSixcomposite target are studied. Ta‐rich (Si/Ta atom ratio,x=1.83) and Si‐rich (x=2.60) films are deposited by dc magnetron sputtering on Si substrates. In Ta‐rich films, a silicidation reaction occurs with annealing above 700 °C. As a result, Si composition,x, and silicide film thickness increases with consuming Si substrate. Stress changes abruptly from tensile to compressive with this reaction. This stress change leads to peeling in the Ta‐rich film during the silicidation reaction. In Si‐rich films, excess Si precipitates at the interface at 750 °C. However, the stress changes more gently in the Si‐rich film and a more uniform TaSi2/Si interface is formed. Therefore, peeling can be avoided in Si‐rich films.

ISSN:0021-8979    

DOI:10.1063/1.347112

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thin films of CuGaSe2have been produced by rf sputtering. Compositional, structural, electrical, and optical properties are strongly influenced by growth temperature. At substrate temperatures lower than 300 °C amorphous or poorly crystalline Se‐excess films are obtained, showing high resistivity (≊103&OHgr; cm) and optical transitions at 1.62, 1.80, and 2.4 eV (values lower than the single‐crystal counterparts). At the higher growth temperatures, polycrystalline films are obtained (average grain size 0.7 &mgr;m) with lower values of resistivity (1 &OHgr; cm), and optical transitions at 1.68, 1.90, and 2.55 eV (very close to the single‐crystal values). A hopping conduction mechanism has been detected at the lower measuring temperature (T<150 K), and a grain boundary limited conduction process at the higher measurements temperature (T>150 K). Structural and compositional characteristics are used to explain the behavior observed in the electrical and optical properties.

ISSN:0021-8979    

DOI:10.1063/1.347113

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The results analyzed, all from previous work, are for W‐Al2O3(as prepared and annealed; 300 K) and Ni‐SiO2(4.2 and 291 K). These results, in which the resistivity changes from 10−5to 107&OHgr; cm as the metal volume fraction is varied, can all be quantitatively fitted to a general effective media (GEM) equation. The GEM equation was developed as an interpolation between Bruggeman’s symmetric and asymmetric media equations for ellipsoidal grains. It has four parameters. The conductivities of the low [&sgr;(lo)] and high [&sgr;(hi)] conductivity components,fc=(1−&Jgr;c), where &Jgr;cis the critical (percolation) volume fraction of the &sgr;(hi) component andtis an exponent.fis the volume fraction of the dielectric or &sgr;(lo) component. As, when &sgr;(lo)=0 or &sgr;(hi)=∞ the GEM equation reduces to the percolation equations, it can also be regarded an interpolation formula between these equations. The W‐Al2O3(as prepared; 300 K) and Ni‐SiO2(291 K) results need a five‐parameter fit as &rgr;(hi) [1/&sgr;(lo)] is modeled as an intergranular tunneling process with &rgr;(hi)=&rgr;(0)exp{C[(1−fc)/(1−f )]1/3−1}, &rgr;(0) andCbeing variable parameters. The log rms deviations for fits are W‐Al2O3(as prepared) 3.3%, W‐Al2O3(annealed) 0.66%, Ni‐SiO (4.2 K) 2.3%, and Ni‐SiO2(291 K) 1.3%.

ISSN:0021-8979    

DOI:10.1063/1.347114

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Current fluctuations with discrete levels, which are called random telegraph signals (RTSs), have been studied in small size metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) from both viewpoints of relative current change and of correlated switchings. A large relative current change of as much as 30% has been observed, even at room temperature. It behaves similarly as normal small RTSs in terms of statistics and temperature dependence. RTSs have been found also in 20‐&mgr;m channel width MOSFETs. These results require another mechanism to explain RTSs in addition to simple Coulomb scattering or number fluctuation. It is emphasized that an interaction between defects at the Si/SiO2interface is necessary to understand the correlated RTSs. The experimental results are reasonably reproduced by a model calculation assuming interacting defects. It is also pointed out that new RTSs generated by electrical stress might be a serious concern in lower submicron devices.

ISSN:0021-8979    

DOI:10.1063/1.347116

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High‐pressure measurements of thermionic emission (TE) and of resonant tunneling in Ga1−xAlxAs/GaAs double barrier structures are reported, wherex=1 or 0.33. Forx=1, TE in a structure with a very narrow well yields a direct measurement of ∼150 meV for the &Ggr;‐X barrier height, and a shift of ∼−11 meV/kbar. For a structure with a well width of ∼70 A˚ and barriers of ∼40 A˚, negative differential resistance (NDR) is observed, which is suppressed at a pressure of ∼8 kbar, when the height of the &Ggr;‐X barrier is approximately equal to the confinement energy of the state in the well. Forx=0.33, and in samples with spacer layers, the same criterion for suppression of the NDR applies as forx=1. When spacer layers are absent, anomalies occur in the variation of the first NDR resonance with pressure, and for sufficiently large samples, the threshold for loss of NDR is much lower than expected. The anomalous behavior is related to the higher concentration of impurities in the barriers. The low‐pressure threshold of the anomaly, and the dependence of the anomaly on sample size, suggest that impurity correlation may play a significant role in the suppression of NDR. At low pressures, or in the absence of anomalies, the pressure dependence of the peak and valley currents of all resonances which are always in the range −1% to −3%/kbar, indicates that the &Ggr; profile controls the tunneling, through the pressure dependence of the effective mass.

ISSN:0021-8979    

DOI:10.1063/1.347117

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

X‐ray photoelectron spectroscopy studies of CdTe‐GaAs interfaces are reported. The growth start of CdTe on GaAs can be nearly stoichiometric if convenient growth parameters are chosen. The valence‐band offset between these two materials is found to be large (470 meV). Cd‐Te‐metal‐GaAs multilayers have been grown with very thin metal films. The CdTe‐GaAs band offset is not influenced by such intermediary metal layers. The experimentally obtained value for the valence‐band offset is compared with recent theoretical calculations taking into account interface dipoles.

ISSN:0021-8979    

DOI:10.1063/1.347118

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The Hall effect of BiSrCaCuO thin film is studied in the temperature range of 2–300 K. In the normal state the Hall‐effect data show a holelike carrier conduction and the Hall coefficient decreases slowly with increasing temperature. The hole density obtained at room temperature is 3×1021cm−3. Near the superconducting transition temperature (TMid=83 K), the Hall coefficient shows a rapid change and drops sharply from a positive value to a negative minimum value with decreasing temperature.The possible physical meaning of the obtained results is discussed.

ISSN:0021-8979    

DOI:10.1063/1.347119

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Insitugrowth of highly oriented YBa2Cu3O7−xthin films (200–500 nm in thickness) has been obtained by pulsed KrF (248 nm) laser ablation on both rigid and flexible randomly oriented polycrystalline yttria‐stabilized zirconia substrates. It is shown thatc‐axis‐perpendicular YBa2Cu3O7−xfilms with a mosaic spread of only 1.0° can be grown on these randomly oriented polycrystalline substrates. Superconducting thin films were obtained withTc(R=0)∼89 K on well‐polished substrates. For the films deposited on the flexible substrates, the superconductingTcis not degraded by repeated bending of the flexible substrate/film composite over a 2.25‐cm‐radius arc although the normal‐state resistivity increases slightly, suggesting the creation of microcracks. The YBa2Cu3O7−xfilms grown on rigid polycrystalline yttria‐stabilized zirconia substrates have a critical current densityJc(H=0)∼1400 A/cm2at 77 K.

ISSN:0021-8979    

DOI:10.1063/1.347121

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

YBa2Cu3O7−xcompounds were extruded into long wires with the diameter of 1 mm after sintering. The sintered wires were subsequently zone melted to develop a highly textured microstructure. Magnetization experiments at 77 K indicated aJcvalue of 1×105A/cm2at 1 T. Transport measurements at 77 K showed a greatly enhanced field dependence of the critical current density. Transmission electron microscopy revealed an important grain‐boundary feature which eliminated the weak‐link behavior. Large amounts of dislocations have also been found in the zone‐melted sample which may contribute to flux pinning in the system.

ISSN:0021-8979    

DOI:10.1063/1.347122

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have theoretically and experimentally analyzed the laser‐induced evaporation process for deposition of superconducting thin films from bulk targets. The spatial thickness variations have been found to be significantly different from a conventional thermal deposition process. Unlike a cos &thgr; thickness variation expected from a thermal evaporation process, the laser evaporation process is characterized by a forward‐directed deposit with a sharp variation in its thickness as a function of distance from the center of the deposit. We have studied in detail the interactions of nanosecond excimer laser pulses with bulk YBa2Cu3O7targets leading to evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating the pulsed laser evaporation (PLE) process has been developed. This model considers an anisotropic three‐dimensional expansion of the laser‐generated plasma, initially at high temperature and pressure. The forward‐directed nature of laser deposition has been found to result from anisotropic expansion velocities of the plasma edges arising due to the density gradients in the gaseous plasma.The physical process of the laser ablation technique for deposition of thin films can be classified into three separate interaction regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation and initial isothermal expansion, and (iii) adiabatic expansion leading to deposition of thin films. The first two regimes occur during the time interval of the laser pulse, while the last regime initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is nonthermal as a result of interaction of the laser beam with the evaporated material. The expansion velocities of the plasma edges are related to the initial dimensions and temperature of the plasma, and the atomic weight of the respective species present in it. Preliminary calculations have been carried out on spatial thickness variations as a function of various parameters in PLE deposited thin films. The effects of the various beam and substrate parameters including energy density and substrate‐target distance affecting the nature of deposition of superconducting thin films have been theoretically examined. Experimental results have been obtained from thin films deposited on silicon substrates by XeCl pulsed excimer laser (&lgr;=308 nm, &tgr;=45×10−9s) irradiation. The spatial thickness and compositional variations in thin films have been determined using Rutherford backscattering technique and the results compared with the theoretical calculations.

ISSN:0021-8979    

DOI:10.1063/1.347123

出版商:AIP    

年代:1990

数据来源: AIP