摘要:

Fabrication processes of metal‐oxide‐semiconductor (MOS) capacitors onn‐type, Si‐face 6H‐SiC, and its electrical properties, have been reported in this article. The effects of thermal oxidation conditions at temperatures between 1150 and 1250 °C on the electrical properties of MOS capacitors were studied. After oxidation, the wafers were annealed under argon ambient to improve the capacitance‐voltage (C‐V) characteristics. TheC‐Vcharacteristics of the Al‐SiO2‐SiC metal‐oxide‐semiconductor capacitors were measured at high frequency in the dark and under illumination. Under dark conditions, inversion did not occur, probably owing to the absence of minority carriers due to the large band gap of 6H‐SiC. TheC‐Vmeasurements made under illumination for both wet and dry thermally grown oxides show accumulation, depletion, and inversion regions. The ac conductance method was used to determine the interface trap densities and emission time constants of fast states. From the analysis of the data a total of fixed charges and the slow interface traps,Not+NitSlowof 1.5–3.3×1012cm−2, fast interface trap densities,NitFastof 0.5–1.7×1011cm−2 eV−1, and an emission time constant of 0.3–1.4 &mgr;s were obtained for wet oxidation. For dry oxidation,Not+NitSlowof 3.5–11.2×1011cm−2,NitFastof 0.7–1.25×1010cm−2 eV−1, and emission time constants of 0.6–2 &mgr;s were obtained.

ISSN:0021-8979    

DOI:10.1063/1.353270

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Schottky characteristics of undoped AlInAs grown by metal‐organic chemical‐vapor deposition have been investigated.I‐Vcharacteristics and their dependence on donor concentrations in AlInAs layers were explained well by assuming the existence of an interfacial layer. The presence of oxygen atoms at the metal‐AlInAs interface was revealed by Auger electron spectroscopy measurements. The oxide formation on AlInAs surface may be an inevitable result because of the high composition of aluminum atoms in AlInAs. Reduction in donor concentration in AlInAs layers is effective in minimizing the influence of the interfacial layer on barrier height lowering. Reduction in gate leakage current was successfully demonstrated for fabricated GaInAs/AlInAs high‐electron‐mobility transistors by reducing donor concentration in AlInAs Schottky layers.

ISSN:0021-8979    

DOI:10.1063/1.353245

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The close‐spaced vapor transport (CSVT) technique is used to grow GaAs epitaxial layers from variousn‐ orp‐type doped GaAs sources. The transport agent is H2O withPH2O= 4.58 Torr.n‐type layers can be grown with Te‐ or Ge‐doped GaAs sources. The transport coefficients of both dopants (ratio of the electrically active dopant concentration in the layer to the electrically active dopant concentration in the source) is 100% for Te or Ge, in the substrate temperature range comprised between 750 and 850 °C.p‐type layers are obtained with Zn‐doped GaAs sources. The transport coefficient of Zn is about 1% and is also independent of the substrate temperature. The transport coefficients and their independence on temperature are in agreement with a mass‐transport controlled model based on the hypothesis that the transport reactions of GaAs and the doping impurities are in equilibrium at the source and substrate temperatures. Si‐doped GaAs cannot be used as a source to obtain conductiven‐type layers. When undoped semi‐insulating (SI)‐GaAs wafers are used as sources in CSVT,n‐type layers are obtained. They are characterized byND−NA=9×1015–3×1016cm−3and &mgr;300K=3000–4000 cm2 V−1 s−1, independent of the temperature, in the temperature range investigated. Glow discharge mass spectroscopy analyses performed on a source and on a layer indicate that C, O, Si, and S are the major residual impurities in the GaAs layer. All these impurities have their origin in the technique (reactor, transport agent). Ge is also present in the layers, as indicated by photoluminescence. It is a minor impurity. Its origin is probably the SI‐GaAs source.  

ISSN:0021-8979    

DOI:10.1063/1.353246

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Quantum corrections to dc current are calculated in two single‐electron devices: turnstile and pump. These corrections set the ultimate limitation on accuracy of these devices as fundamental standards of dc current. A developed approach can be used in principle to analyze macroscopic quantum tunneling of charge in arbitrary single‐electronic circuit.

ISSN:0021-8979    

DOI:10.1063/1.353247

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Field‐effect deep‐level transient spectroscopy studies have been carried out in molecular‐beam‐epitaxy‐grown GaAs onn+‐GaAs implanted with Si. Four electron traps and one weak hole trap have been detected. Thermal‐emission rate, capture cross section, and activation energy have been found to be influenced by the applied field; the effect was particularly significant in the case of the EL2 level. The energy versus field plots have shown a general tendency that the applied field modulates the activation energy of the trap states; for example, the Arrhenius plot of a single EL2 level at lower fields (<−3 V/cm) is split up into as many as three at higher fields (≳−4 V/cm). These results have been interpreted in terms of recent theories of electron‐phonon interaction on the electron emission from the trap states to the conduction band.

ISSN:0021-8979    

DOI:10.1063/1.353248

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We investigate the temperature dependence of Schottky barrier heights on silicon. The analysis of a large variety of polycrystalline diodes shows that the temperature coefficient of the barrier height depends on the chemical nature of the metal. This observation is in contradiction with models suggesting Fermi‐level pinning at the center of the semiconductor’s indirect band gap. From the analysis of epitaxial NiSi2/Si Schottky contacts, we conclude that there is a direct influence of interface crystallography on both the barrier height and its temperature dependence. Finally, we present some new results on the pressure coefficient of barrier heights. Pressure and temperature coefficients of polycrystalline Schottky contacts are correlated similarly to the pressure and temperature coefficients of the band gap.

ISSN:0021-8979    

DOI:10.1063/1.353249

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

When a magnetic dipole passes through a hollow YBa2Cu3Oxcylinder, the dipole is decelerated as a result of the energy dissipation in the superconductor. This energy loss is evaluated on the basis of a macroscopic theory that incorporates both the hysteresis and flux‐flow losses. The results are in reasonably good agreement with the experiments conducted using Nd‐Fe‐B magnets.

ISSN:0021-8979    

DOI:10.1063/1.353250

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Superconducting thin films of Sn‐doped In2O3with high visible transmittances were prepared by electron‐beam evaporation on polyester and glass substrates, followed by post‐deposition annealing. Effects of annealing on electrical and optical properties were examined and optimum conditions under which superconductivity appears were determined. With increasing annealing temperature or annealing time, films change their electrical conduction from semiconducting to metallic behavior, and the superconducting state could be obtained in the transition region between the two phases. Post‐oxidation at a low temperature (∼140 °C) is important to produce superconducting films, which have transition temperaturesTcof 2–4 K for resistivities of the order of 10−3&OHgr; cm and carrier densities in the range of 1021cm−3. Superconducting films with much higher transmittance (∼80% at the wavelength 550 nm) were obtained on polyester substrates, whereas glass substrates were used to produce films with higherTc’s and lower resistivities. The temperature variations of the resistivity nearTcand of the perpendicular critical field can be reconciled with those expected for a dirty superconducting thin film. It is found that theTcis well correlated with the resistivity and transmittance, and that the superconducting state appears in restricted ranges of these parameters. Chemical bonding and valence‐band structures in films were measured by means of x‐ray photoelectron spectroscopy. The present results are compared with those for other superconducting oxides including high‐Tccuprate systems. The appearance of superconductivity in our samples is discussed on the basis of the electrical, optical, and chemical properties.

ISSN:0021-8979    

DOI:10.1063/1.353251

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The long‐term stability of epitaxial thin film structures of superconducting Y1Ba2Cu3O7−xon silicon wafers (100), using a yttria‐stabilized ZrO2(YSZ) buffer, is presented and compared to identical structures on SrTiO3(100) and yttria‐stabilized ZrO2(100) single crystals. For Y1Ba2Cu3O7−y/YSZ/Si heterostructures, the maximum Y1Ba2Cu3O7−yfilm thickness is limited to 50 nm; otherwise thermal strain induces microcracks. Thinner films are more stable, but nevertheless show aging over several weeks, which affects critical current density and room‐temperature resistivity, but not the critical temperatureTc.  

ISSN:0021-8979    

DOI:10.1063/1.353252

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Large enhancements in the width of the magnetization hysteresis were obtained by neutron irradiating Bi2Sr2CaCu2Oxand Bi2Sr2Ca(Cu1−yLiy)2Oz. By inducing Li(n,3T)&agr; reactions, high‐energy ions are produced, allowing a direct comparison of the effects of neutron damage and ion damage in polycrystalline powders. It is shown that the ion damage leads to significantly greater magnetization enhancements, particularly at intermediate temperatures (5, 30, and 77 K results are compared). Significant differences in the magnetic field and temperature dependencies of the induced pinning are quantified.

ISSN:0021-8979    

DOI:10.1063/1.353253

出版商:AIP    

年代:1993

数据来源: AIP