摘要:

Monte Carlo calculation on steady‐state electron transport properties in uncompensated and compensated Al0.25In0.75As at several lattice temperatures is reported. It is found that alloy scattering has a significant effect on electron drift velocities at high fields, and that the electron velocity‐electric field characteristics of compensated Al0.25In0.75As exhibit less temperature dependence than uncompensated Al0.25In0.75As. The small &Ggr; valley effective mass and the large &Ggr; toLand &Ggr; toXvalley separations of Al0.25In0.75As result in the excellent low‐field mobilities and the peak velocities in comparison to those of GaAs, InP, and In0.53Ga0.47As over the range of doping compensations considered.

ISSN:0021-8979    

DOI:10.1063/1.345081

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Electrical phenomena in metal‐oxide‐semiconductor capacitors caused by Fowler–Nordheim tunneling injection of electrons have been studied at temperatures ranging from 77 to 300 K. It has been found that the shift of flatband voltages (&Dgr;VFB) depends on the oxidation temperature and that low‐temperature oxidation is desirable for the reduction of &Dgr;VFB. The dependence of &Dgr;VFBon the injection temperature shows a characteristic feature: The &Dgr;VFBreduces with decreasing injection temperature in the range above 180 K and, on the other hand, is almost independent of the injection temperature in the range below 180 K. These results are mainly attributable to the injection temperature dependence of interface state generation. The injection temperature dependence of interface state density clearly indicates that two generation mechanisms of interface states are present. In addition, we have found a power‐law dependence of the generated interface states on &Dgr;VFB, independent of oxidation and injection conditions.

ISSN:0021-8979    

DOI:10.1063/1.345082

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The crystallinity of GaAs grown on Si with various intermediate layers by metalorganic chemical vapor deposition and characteristics of Schottky diodes fabricated on the grown GaAs/Si have been studied. The GaAs/Si with an Al0.55Ga0.45P intermediate layer has both good crystallinity, x‐ray full width at half maximum of 188 arc sec, and a smooth surface. The Schottky diode fabricated on the GaAs/Si with an Al0.55Ga0.45P intermediate layer also shows good forward and reverse current‐voltage characteristics with an ideality factor of 1.06, as good as for ann‐type GaAs substrate. However, a relatively large leakage current is observed under reverse and small forward bias. This leakage current is caused by generation and recombination through the centers related to dislocations in the GaAs/Si.

ISSN:0021-8979    

DOI:10.1063/1.345083

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Measurements have been made of the electrical conductivity of sputtered rare‐earth–transition‐metal films. The Wiedemann–Franz law has been used to relate these values to the electronic component of the thermal conductivity of the films. A small lattice contribution to the thermal conductivity was estimated and added to the electronic component to obtain the total thermal conductivity of the materials. This total thermal conductivity is about one order of magnitude smaller than that of the pure bulk materials composing the films. Knowledge of the thermal conductivity of such rare‐earth–transition‐metal films has proved to be useful in the modeling of the thermomagnetic recording processes. These processes are used to record information on magneto‐optic data storage disks.

ISSN:0021-8979    

DOI:10.1063/1.345084

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Avalanche breakdown in abruptp‐nAlGaAs/GaAs heterojunctions is invesigated, and the breakdown voltage, the maximum electric field, and the depletion layer width are calculated as functions of the doping densities, the temperature, and the AlAs mole fraction in AlGaAs. The model employed is an extension of Hauser’s model of homojunction breakdown [Appl. Phys. Lett.33, 351 (1978)], and it includes the effects of the band offsets at the interface.

ISSN:0021-8979    

DOI:10.1063/1.345085

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new technique, oxide current relaxation spectroscopy, has been presented for observing various traps and/or charges in the thin oxide. This technique is based on electron‐fluence‐dependent current characteristics in tunneling metal‐oxide‐semiconductor structures under high field stresses. It is capable of showing the spectrum of traps and/or charges in the thin‐gate SiO2as positive and negative peaks on an axis as a function of electron fluence. The height and position of each spectrum peak are related to the density, centroid, and capture cross section of the corresponding kind of the traps and/or charges. The parameters of various traps and/or charges in the thin SiO2have been measured. The experimental results are consistent with theoretical calculations.

ISSN:0021-8979    

DOI:10.1063/1.345086

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A critical‐state calculation of the magnetization of hard type‐II superconducting grains having anisotropic critical‐current densities is given. The analysis shows how the critical‐current densities should be deduced from magnetization measurements for various grain morphologies. A universal curve of the magnetization hysteresis versus one of the grain dimensions is presented, showing that the hysteresis does not change linearly with grain size. Applications to single crystals and to bulk materials are made.

ISSN:0021-8979    

DOI:10.1063/1.345087

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Hot isostatic pressing and heat treatments in high‐pressure oxygen were used to study the effect of pressure on the stability of YBa2Cu3O7−x. At 875 °C the compound decomposes at an oxygen pressure of about 7 bars. The decomposition involves formation of Y2BaCu3O5and a Ba‐Cu oxide phase. Formation of the latter phase involves additional oxidation because this phase can contain as many as 1.5 oxygen atoms per barium atom. The decomposition can most simply be visualized by considering the chemical reaction 2(YBa2Cu3O7−x)+( (1)/(4) +x−y/2)O2→Y2BaCuO5+Ba3Cu5O9.5−y. Encapsulated samples also decompose during hot isostatic pressing, but the process appears to be more complex. The compound YBa2Cu4O8was detected in addition to the two products observed in oxygen‐treated samples. The reaction above, with YBa2Cu3O7−xserving as an oxygen source, aids in understanding the microstructural observations for encapsulated samples. Decomposition can be completely reversed by annealing in air for 20 h at 875 °C.

ISSN:0021-8979    

DOI:10.1063/1.345088

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The dependence of the effective surface impedanceZeff=Reff+iXeffof superconducting thin films on the film thicknessd, on the magnetic field penetration depth &lgr;, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistanceReffcan be expressed byRSf(d/&lgr;)+RtranswhereRSis the intrinsic surface resistance of the superconductor. The functionf(d/&lgr;) describes the altered current density distribution in the film.Rtransarises from power transmission through the film. It depends ondand &lgr; as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactanceXeffof a superconducting thin film can be expressed byXS cosh(d/&lgr;) whereXS=&ohgr;&mgr;0&lgr; is the intrinsic surface reactance. Measurements ofZeffat 87 GHz have been performed for YBa2Cu3O7−&dgr;thin films grown epitaxially by laser ablation on SrTiO3, MgO, and LaAlO3. With the best films,Reff(77 K) values of 21 m&OHgr; andRS(77 K) values of 8 m&OHgr; were achieved. The temperature dependence of &lgr; was found to be in good agreement to both weak‐coupling BCS theory in the clean limit and the empirical two‐fluid model relation with &lgr; (0 K) values ranging from 140 to 170 nm and 205 to 250 nm, respectively.

ISSN:0021-8979    

DOI:10.1063/1.345037

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconducting, silver‐doped films of Y1Ba2Cu3O7−&dgr;have been deposited by spray pyrolysis of aqueous nitrate solutions onto MgO substrates. The superconducting transport properties, microstructure, and microwave losses have been characterized for various amounts of AgNO3added to the spraying solution. These films had resistive transition temperatures between 79 and 85 K with widths from 3 to 7 K. The room‐temperature resistivity was a strong function of the silver doping, dropping by a factor of 50 for the heavily doped films. Critical current densities at 4 K were typically several 103A/cm2with little correlation to the silver doping. Lattice constants also were not significantly affected by the silver doping level, however, lightly doped films were denser, had the strongestcaxis preferred orientation, and a smoother surface. Rf surface resistance was measured at 18 GHz, and for the best films dropped a factor of 10 below copper by 40 K. The London penetration depth was estimated to be approximately 1 &mgr;m for the best films.

ISSN:0021-8979    

DOI:10.1063/1.345038

出版商:AIP    

年代:1990

数据来源: AIP