摘要:

This paper describes the characteristics of thin fluoride films on InP which are used as dielectric for metal‐insulator‐semiconductor (MIS) devices. Films of Ba1−xSrxF2(x=0.0, 0.5, 0.83, and 1.0) were deposited by sublimation of mixtures of BaF2and SrF2in vacuum under 10−5Torr pressure. The composition of the films was deduced from x‐ray diffraction and energy dispersion analysis by x‐ray studies. The electrical activation energies of the films determined between 120 and 300 K were found to be 3.5–22.0×10−3eV , depending on composition and temperature. The resistivity of the films was in the range of 5.0×1011to 5.0×1012&OHgr; cm with the breakdown fields greater than 5.0×105V cm−1. The interface state density obtained was as low as 5×1010cm−2 eV−1with annealed BaF2films. Scanning electron microscope studies showed that annealing caused development of cracks resulting in decreased film resistivity. Auger studies gave evidence of broadening of the interface and outdiffusion from the substrate due to annealing.

ISSN:0021-8979    

DOI:10.1063/1.345016

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ion‐beam‐sputtered indium‐tin oxide (ITO) films were studied as a function of the oxygen pressurePO2, during deposition. Analysis of electrical transport measurements, Auger electron spectroscopy (AES), and x‐ray photoelectron spectroscopy (XPS) show a self‐consistent correlation of all the results. With increasingPO2a monotonous decrease is observed in the carrier density, which is found to be directly proportional to the oxygen vacancy concentration. This is based on a direct evaluation of the concentration of In unoxidized species in the film using AES and XPS. The moderate decrease of the electron mobility asPO2is increased is also attributed to the change in the film oxidation state. The systematic relations between all the parameters investigated in this study yield a better understanding of the deposition process and point in the direction of achieving the best ITO films.

ISSN:0021-8979    

DOI:10.1063/1.345017

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The interfacial microstructure and electrical properties of the Pt/Ti ohmic contact top‐In0.53Ga0.47As (Zn: 5×1018cm−3) formed by rapid thermal processing (RTP) were intensively studied. Significant interdiffusion of Ti, In, and As across the interface, driven by RTP, occurred at temperatures of, or above, 350 °C for a heating duration of 30 s. A minimum specific contact resistance (9.0×10−6&OHgr; cm2) was achieved after heating at 450 °C. Cross‐sectional transmission electron microscopy of this sample revealed an interfacial reaction zone with complicated microstructure, and the dominant interfacial compound was identified to be InAs. Further increase in RTP temperature resulted in a change in the microstructure, and degradation of the contact resistance. The temperature‐dependence characteristic of the specific contact resistance of as‐deposited Pt/Ti contact to InGaAs revealed a thermionic‐emission‐dominated carrier‐transport mechanism with an effective barrier height &fgr;b, of 0.13 V. RTP treatment to the sample at elevated temperatures up to 450 °C decreased the temperature dependence of the contact resistance. This phenomenon strongly suggests a partial conversion of the dominant carrier‐transport mechanism across the contact area from thermionic emission to field emission. This was further verified by fitting the temperature dependence of the measured contact resistance to a phenomenological theory based on a linear combination of the two different types of carrier‐transport mechanisms operating at isolated area segments distributed uniformly across the interface.

ISSN:0021-8979    

DOI:10.1063/1.345018

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It is predicted that thin quantum‐well superlattices or spike superlattices of GaAs in ZnSe will produce band gaps in the yellow‐green, and that (GaAs)1−x(ZnSe)xspikes will lead to green and blue‐green gaps. These thin quantum‐well structures should have better doping properties than ZnSe forx<0.6.

ISSN:0021-8979    

DOI:10.1063/1.345019

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High throughput, sharp interfaces, and selective deposition with direct ion‐, electron‐, and photon‐beam‐controlled techniques are some of the key driving forces for the development of superconducting thin films by the metalorganic chemical vapor deposition technique. In this paper, we report on theinsitudeposition of a buffer layer of BaF2and high‐temperature superconducting thin films of Y‐Ba‐Cu‐O by metalorganic chemical vapor deposition (MOCVD) on silicon substrates. These films have an on‐set temperature of 90 K and zero resistance at 73 K. The use of BaF2as a buffer layer on Si substrates suggests the possibility of three‐dimensional integration with high‐temperature superconducting thin films, for hybrid superconductor/semiconductor devices as well as superconducting switches and other related devices. To the best of our knowledge, this is the first report of the deposition of high‐temperature superconducting thin films on Si by MOCVD.

ISSN:0021-8979    

DOI:10.1063/1.345020

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We studied the dynamic electrical properties of epitaxial Y1Ba2Cu3O7−xsuperconducting thin films on strontium titanate and MgO substrates. A fast nonlinear switching of a high‐Tcfilm between the dissipative and superconducting states has been demonstrated. These measurements show that the rise and the fall times of these transitions are faster than 250 ps (which are presumably limited by the speed of the measurement electronics). This fast nonlinear switching may lead to opportunities for new high‐frequency electronic devices including, for example, fast logic gates or threshold devices. We have proposed and demonstrated the application of such a nonlinear switching in a novel noise discrimination scheme for speeds of several hundred MHz. The proposed method is simple and effective in the enhancement of signal‐to‐noise ratio in digital electronic circuits.

ISSN:0021-8979    

DOI:10.1063/1.345021

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

One of the derivatives of the 1‐2‐3 high‐Tcsuperconductors is known as the green phase (Y2BaCuO5). In a novel approach, the latter is proposed as the starting material to make oriented films deposited on MgO (001) by a simple painting method. Best results are obtained with a heat treatment up to 1040 °C and a slow cooling rate from 980 to 920 °C, giving films withTc,50%=83 K and &Dgr;Tc=6 K. Scanning electron microscopy assisted by localized x‐ray fluorescence permitted us to correlate theTc’s andJc’s with the general morphology of these films. Test pellets made with the 2:1:1 phase are also shown to be superconducting with a transition mid‐point atTc,50%=93 K and width of around 2 K.

ISSN:0021-8979    

DOI:10.1063/1.345022

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of an aluminum oxide layer at the interface of Al/Nb on phase formation in thin‐film binary diffusion couples was studied. Al/Nb bilayers with or without aluminum oxide at the interface were prepared by electron‐beam evaporation. The samples were annealed at a constant heating rate of 50 °C/min to temperatures in the range 800–950 °C, and the progress of the reaction was monitored by x‐ray diffraction and measurement of the superconducting transition temperature. The presence of an aluminum oxide layer at the interface was found to significantly retard the formation of the superconductingA15 Nb3Al phase.

ISSN:0021-8979    

DOI:10.1063/1.345023

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial YBa2Cu3O7films were fabricated on (100) SrTiO3substrates by the pulsed laser (&lgr; =308 nm, &tgr;=45×10−9s) evaporation of bulk targets in a controlled oxygen atmosphere (partial pressure 100–600 mTorr). The nature of epitaxial growth and orientation of the film was controlled by the oxygen partial pressure in the chamber and the substrate temperature during the deposition process. These parameters were also important in determining the superconducting properties of the thin films. The best films exhibited zero electrical resistance at about 90 K with very high critical current densities. Thin single‐crystal films were growninsituat substrate temperatures greater than 550 °C with thecaxis perpendicular to the substrate, whereas films deposited at lower substrate temperatures showed a mixture ofc‐ andaaxes perpendicular to the substrate. The films deposited in high vacuum or low oxygen partial pressure (<1 mTorr) and further annealed at high temperatures (∼900 °C) in oxygen showed rectangular grains with thecaxis parallel to the substrate. Higher‐temperature (>920 °C) annealed films showed different surface morphology with thecaxis perpendicular to the substrate. The epitaxial growth of YBa2Cu3O7films on (100) SrTiO3substrates is examined as a function of lattice mismatch between the thin film and the substrate. As thea’andcaxes of the tetragonal unit cell (above transformation temperature) of YBa2Cu3Oxvaries both with the temperature and the oxygen content, a new method is proposed to calculate the lattice parameters of the superconducting phase. This method is based on the lattice parameters calculation at the tetragonal to orthorhombic transformation temperature which always occurs approximately at the same oxygen content regardless of the processing oxygen partial pressure.

ISSN:0021-8979    

DOI:10.1063/1.345024

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A pinning force acting upon a periodic fluxon chain in a long Josephson junction with a commensurable periodic lattice of local inhomogeneities is calculated by means of a perturbation theory. The pinning force for a single fluxon is also calculated. Dynamics of a chain and of a single fluxon are also studied. The experimental part of the paper reports results of measurements of a critical bias currentIcversus external magnetic fieldH. The measurements have been performed for long overlap Nb‐NbOx‐Pb junctionsIc(H) curve were observed at multiple values ofH. Agreement between the theory and experiment for different spatial periods of the fluxon chain is satisfactory.

ISSN:0021-8979    

DOI:10.1063/1.345025

出版商:AIP    

年代:1990

数据来源: AIP