摘要:

GaxIn1−xAsyP1−ylayers were grown on InP substrates by gas‐source molecular beam epitaxy in order to study the electrical and optical properties of the quaternaries. Hall mobilities and carrier concentrations of Si‐ and Be‐doped quaternary layers were compared in the alloys for different wavelengths. Smaller hole concentrations were observed for the alloy compositions close to InP than for those close to GaInAs grown with the same Be cell temperature. In addition, the highest achievable hole concentration was found to be a function of the alloy composition. Possible reasons for the observations are discussed. The influence of pregrowth treatments on the measured Hall mobilities and carrier concentrations due to the changes in the substrate‐epilayer interfacial conductivity was studied. Room‐temperature photoluminescence results are also presented.

ISSN:0021-8979    

DOI:10.1063/1.354375

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The steady‐state charge‐balance‐related properties of semiconductor junctions between highly dopedn‐type epitaxial layers of GaAs and semi‐insulating GaAs substrates are examined. Specific results are obtained for the three most common defect compensation mechanisms within the semi‐insulating material: (i) a deep donor interacting with a shallow acceptor, typified by the case of the EL2 defect and background carbon, respectively; (ii) a shallow donor and a deep acceptor, as would occur for heavy levels of silicon and chromium; and (iii) a deep donor and a deep acceptor, as would be typical of EL2 and light levels of either chromium or a complementary antisite defect. Electrostatic properties, including Fermi‐level positions, built‐in potentials, asymptotic electric‐field profiles, and junction capacitance are analytically derived based upon Hall/Shockley–Read models of the defect states and these are additionally compared against numerical solutions which implement the same models. Junction boundary conditions that pertain to the high‐level injection case normally encountered in these junctions are also analytically derived and verified by numerical simulation. Limitations on the applicability of standard step‐profilep‐n–junction theory are discussed, as are necessary considerations for proper numerical modeling.

ISSN:0021-8979    

DOI:10.1063/1.354376

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Quantum waveguide structures with double‐bend discontinuities were fabricated in modulation‐doped AlGaAs/GaAs heterojunctions using a split‐gate technique. The low field ac‐conductance measurements at 50 mK show resonant peaks in the lowest quantized conductance plateau. The number of peaks increases with the effective cavity length of the double bend. This observation may be explained in terms of the allowed standing waves in the bend cavity, which is consistent with the theoretical predictions of a generalized mode‐matching theory. Beyond the simple waveguide behavior, we find that the measured peak conductivity decreases as the channel length increases, which is believed to be associated with elastic scattering due to channel inhomogeneities. Magnetic field studies show that the resonance features are suppressed as the cyclotron radius approaches the one‐dimensional channel width.

ISSN:0021-8979    

DOI:10.1063/1.354377

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

High‐field effects in metal‐oxide‐semiconductor capacitors have been studied in detail. A comprehensive set of experiments, stressing identically fabricated capacitors on bothP‐type andN‐type silicon, both in accumulation and in inversion, has been made to study defect generation in the oxide at high fields. There is clear experimental evidence that both bulk hole and electron traps are generated under all stress conditions. High‐field prebreakdown properties depend mainly upon the dynamics of generation of traps, trapping and detrapping at these and in previously existing traps. It has been found that of several processes, some dominate, depending upon the type of silicon and polarity during stressing, and this is also true for the final breakdown mechanism. In this paper the dominant mechanisms are identified for each of the field stress conditions that have been studied.

ISSN:0021-8979    

DOI:10.1063/1.354378

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The reaction mechanism for electrochemical‐vapor deposition of yttria‐stabilized zirconia was studied. Yttria‐stabilized zirconia films were deposited on porous La(Sr)MnOxusing the electrochemical‐vapor‐deposition process. The distribution of yttria concentration through the film was investigated by means of secondary‐ion‐mass spectroscopy and x‐ray microanalysis and found to be nearly constant. The deposition rate was approximately proportional to the minus two‐thirds power of the film thickness, the one‐third power of the partial pressure of ZrCl4/YCl3mixed gas, and the two‐thirds power of the product of the reaction temperature and the electronic conductivity of yttria‐stabilized zirconia film. These experimental results were explained by a model for electron transport through the YSZ film and reaction between the surface oxygen and the metal chloride on the chloride side of the film, both of which affect the deposition rate. If the film thickness is very small, the deposition rate is thought to be controlled by the surface reaction step. On the other hand, if large, the electron transport step is rate controlling.

ISSN:0021-8979    

DOI:10.1063/1.354379

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

p‐Type microcrystalline Si films have been prepared by rf decomposition of SiH4/H2/BF3gases. The gas composition, substrate temperature, and rf power dependence of film conductivity &sgr; are investigated. The &sgr; increases with increasing BF3and saturates or takes a maximum at [BF3]/[SiH4]∼1. A fairly high &sgr; value of ∼1.2×10−2S/cm is obtained for the low rf power (∼0.1 W/cm2). Increasing rf power decreases &sgr;, which is in contrast to the SiH4/H2/B2H6system. The incorporation rate of boron from gas phase into the film is found to be low (∼4%) by use of secondary ion mass spectroscopy. Increasing hydrogen increases &sgr;. Temperature is found to be the most effective deposition parameter. The &sgr; monotonically increases with an increase of substrate temperatureTS. Transmission electron microscopy observation shows that films with higher &sgr; contain higher density or larger size Si crystallites. The crystalline size increases by a short time (≤15 min) annealing at 400 °C. The deposition parameter dependence of &sgr; in comparison to the SiH4/H2/B2H6system is discussed. The low temperature annealing effect is discussed in terms of film structure.  

ISSN:0021-8979    

DOI:10.1063/1.354380

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Superconducting Ba1−xKxBiO3(BKBO) thin films and heteroepitaxial multilayers were deposited byinsituoff‐axis sputtering on various substrate at 400 °C. A typical superconducting BKBO thin film on the SrTiO3and MgO substrates had a very sharp zero resistance transition at a temperature of 22–24 K as measured by transport four point and mutual inductance probes. The normal state resistivity exhibited metallic to semiconductive characteristics depending on film composition with the lowest room temperature resistivity of about 0.25 m&OHgr; cm. The film orientation was highly epitaxial to both SrTiO3and MgO substrates. Normal metal‐insulator‐superconductor (NIS) type tunnel functions with native insulator layer and deposited MgO layer were reproducibly fabricated. The superconducting energy gap of about 3.6 meV was obtained from those NIS junctions. Heteroepitaxial superconductor‐ insulator‐superconductor (SIS) trilayer junctions were also fabricated using MgO insulator layers. For a 5 nm thick insulator layer, quasiparticle SIS tunnel junctions with nonhystericI‐Vcharacteristics were obtained. By reducing MgO insulator layer thickness down to 3 nm, SIS tunnel junctions with Josephson supercurrent were obtained with hystericI‐Vcharacteristics.

ISSN:0021-8979    

DOI:10.1063/1.354381

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

14° [001] tilt grain boundaries in YBa2Cu3O7−&dgr;have been found to exhibit anomalously good superconducting critical currents, associated with magnetic flux pinning, although no special interfacial structure has heretofore been associated with this misorientation. We present an analysis of the geometry of the grain boundary in question and show that it can correspond to a special interface, within the definition of constrained lattice coincidence, which may lead to new understanding of the superconducting behavior of grain boundaries. Our analysis shows that the tetragonal‐to‐orthorhombic phase transformation may have important effects upon grain boundary structure and properties, indicating new approaches to producing high‐current superconductors.

ISSN:0021-8979    

DOI:10.1063/1.354382

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Thin‐film growth and compositional effects ofc‐axis oriented YBa2Cu3O7−x(YBCO) thin films synthesized by metalorganic chemical vapor deposition have been investigated. The formation of single cation films using tetramethylheptanedionate precursors was shown to be mass controlled, exhibiting a ratio of deposited to evaporated species in the increasing order Ba, Y, and Cu. The physical properties of off‐stoichiometric YBCO films deposited on MgO substrates were measured in the compositional range 1.1≤Ba/Y≤2.3 and 1.5≤Cu/Ba≤4.6. While structural properties such asc‐axis values and rocking curves appeared unaffected to variations in cation stoichiometry, morphology was observed to be extremely sensitive even to slight changes in composition. Off‐stoichiometric layers with Cu/Ba≳1.5 were observed to exhibit Cu‐rich precipitates embedded in a 1:2:3 YBCO film matrix. The zero‐resistivity temperatures were above 77 K for all cation film compositions measured. However, sharp ac‐susceptibility transitions were restricted to a more narrow compositional range (1.9<Cu/Ba<3.6). The best superconducting properties [Tc=85 K,Jc(77 K)≳106A/cm2] were observed for films with relatively rough surface morphologies (Ba/Y=1.6 and Cu/Ba=3.5). An optimum trade‐off between smooth surfaces and superconducting properties was found for Ba/Y=1.5 and Cu/Ba=1.9, yieldingTc=81 K andJc(77 K)=3×105A/cm2.

ISSN:0021-8979    

DOI:10.1063/1.354383

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The microstructural origin of magnetic anisotropy in a magnetron in‐line sputter‐deposited CoPtCr/Cr magnetic thin‐film disk was examined by mapping magnetic properties and microstructure. The film coercivity (Hc), remanence‐thickness product (Mr&dgr;), and coercivity squareness (S*) were determined as a function of radial (r) and angular (&thgr;) co‐ordinates using a transfer curve magnetometer. The observed variations inHc,Mr&dgr;, andS* across the disk were 85 Oe, 0.15 emu/cm2, and 0.03, respectively. The angular variation in magnetic properties showed a sinusoidal pattern with the maxima corresponding to the regions where the tracks were parallel (&thgr;=270°) to the pallet movement direction. High‐resolution scanning transmission electron microscopy showed subtle differences in the Co‐alloy grain morphology and crystallographic orientation between &thgr;=270° and &thgr;=360° locations. The grains were equiaxed in general except for a small fraction of grains elongated in the direction of pallet movement. Lattice images clearly showed that about 45% of the Co‐alloy grains had in‐planecaxes and a preferred alignment of thecaxes along the texture groove. A greater preference for thecaxes to lie along the texture line was observed for the &thgr;=270° location. A coherency stress‐based model is proposed to explain the preferredc‐axis alignment. While the crystalline anisotropy appears to be the main factor responsible for the magnetic anisotropy, both crystalline and shape anisotropies contribute to the magnetic anisotropy variations.

ISSN:0021-8979    

DOI:10.1063/1.354384

出版商:AIP    

年代:1993

数据来源: AIP