摘要:

Thin films of aluminum nitride have been deposited at 350 K on Si(100), fused quartz, and KBr substrates using gas‐phase excimer laser photolysis of trimethylamine alane and ammonia at 193 nm. Depth profiles of these laser‐grown films using secondary‐ion‐mass spectrometry indicate that no AlN film is produced without photolytic processes. The films are amorphous, and are smooth and featureless as established by scanning electron microscopy and atomic force microscopy. Optical‐absorption spectra of these films have been measured and a band gap of 5.8 eV has been calculated from these spectra. Ellipsometric measurements have been used to determine a refractive index of 1.9–2.0 for these films. The infrared spectrum of the films displays a characteristic absorption due to TO phonons in AlN. Electrical measurements reveal that the films have excellent dielectric properties. A breakdown electric field of 108V m−1and a low‐frequency dielectric constant of 6.0–6.9 have been established fromI–VandC–Vmeasurements, respectively. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360606

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the growth of unintentionally doped ZnSe by gas‐source molecular beam epitaxy using elemental Zn and thermally cracked hydrogen selenide (H2Se). The dependence of the growth rate on H2Se flow rate indicates that the minority source flux limits the growth. The stoichiometric growth condition is established. It is found that the two‐dimensional growth regime of ZnSe films extends down to 150 °C. The electrical and optical properties of ZnSe epilayers are characterized by Hall and photoluminescence measurements. Undoped ZnSe epilayers shown‐type conduction with an electron concentration of 1.6×1016cm−3and Hall mobility of 490 cm2/V s at room temperature. Low‐temperature photoluminescence spectra of undoped ZnSe epilayers are dominated by neutral donor‐bound exciton emission located at 2.7968 eV. The residual donor impurities of In and Cl are detected in ZnSe epilayers by secondary‐ion‐mass spectroscopy measurements and are responsible for then‐type conduction. It is confirmed that the donor impurities originate from the H2Se gas source. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360607

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Epitaxial growth of CoAl films on AlAs(001) films was examined for films with Co contents of 47–58 at. %. The surface terminations of CoAl films were characterized, and the dependance of surface terminations and surface reconstructions on the Co/Al composition was examined. When AlAs/CoAl/AlAs heterostructures were fabricated by growing AlAs overlayers on CoAl films whose surface terminations were well defined, a mixture of AlAs(001) and AlAs(111) phases grew on the Al‐terminated surface, whereas only the AlAs(001) phase grew on the Co‐terminated surface. The Co‐terminated CoAl surface thus is suitable for the overgrowth of AlAs. A high‐quality epitaxial GaAs/AlAs/CoAl/AlAs/GaAs heterostructure was grown by combining the control of metal surface terminations with low‐temperature migration‐enhanced epitaxial growth of AlAs overlayers. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360608

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Secondary‐ion‐mass spectrometry (SIMS) was used to determine the concentration and depth distribution of B incorporated into Ge(001)2×1 films grown on Ge(001) substrates by gas‐source molecular‐beam epitaxy using Ge2H6and B2H6. B concentrationsCB(3×1016–4×1019cm−3) were found to increase linearly with increasing flux ratioJB2H6/JGe2H6(8.2×10−3–1.7) at constant film growth temperatureTs(300–400 °C) and to increase exponentially with 1/Tsat constantJB2H6/JGe2H6ratio. The difference in the overall activation energies for B and Ge incorporation over this growth temperature range is &bartil;0.22 eV while B2H6reactive sticking probabilities ranged from 8×10−4at 300 °C to 2×10−5at 400 °C. SIMS depth profiles from B modulation‐doped samples and two‐dimensional &dgr; ‐doped samples grown atTs<350 °C were abrupt to within instrumental resolution with no indication of surface segregation. Structural analysis byinsitureflection high‐energy electron diffraction combined with postdeposition high‐resolution plan‐view and cross‐sectional transmission electron microscopy showed that all films were high‐quality single crystals with no evidence of dislocations or other extended defects. B doping had no measurable affect on Ge deposition rates. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360540

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The wettability of the rock surface plays a very important role in the transport of fluid in porous media. The combined Amott‐USBM method currently used for the determination of these values is not able to produce reliable estimates when the surface has an intermediate wettability. The nuclear magnetic resonance (NMR) technique could provide an efficient method if the parameters affected by the wettability could be established in well defined model systems. To obtain information about the effect of wettability changes upon the NMR parameters,T1relaxation time measurements were carried out on1Hand2Hat two different magnetic fields. A large number of well defined consolidated and unconsolidated samples, with different degrees of wettability were used in this study. The results obtained showed that theT1values, as well as the relaxation rate distribution parameters, such as the distribution width, are affected by changes in the wettability. A dependence of theT1wettability data on the magnetic field intensity was also observed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360541

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A partial monolayer of silane, SiH4, adsorbed on a GaAs(100) surface at 40 K may be fixed in a desired pattern by irradiation with an electron microbeam, and then coveredinsituby GaAs grown by molecular‐beam epitaxy. The initial rate of Si coverage under irradiation by 1.5 keV electrons is (0.031±0.005) Si per electron per monolayer of silane. Applications include theinsitufabrication via patterned doping of circuit elements and structures with interesting electronic properties. As an example, we have made an isolated buried channel field‐effect transistor and measured its properties. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360542

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We analyze the second‐harmonic generation process in a microcavity of optical nonlinear material. We show that, in the case when the cavity thickness is much smaller than the material coherence length and for sufficiently high finesses, no phase match procedures are necessary to obtain a quite large optical conversion yield. It is thus possible to capitalize on the large optical nonlinear susceptibilities of III‐V or II‐VI materials though these compounds are not birefringent. It is shown that by adjusting mirror reflectivity phases it is possible to obtain doubly resonant cavities in which there is no phase mismatch between pump and harmonic waves. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360543

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nanometer aerosol particles produced by laser ablation from a carbon target were used to fabricate wires about 50 &mgr;m in diameter by agglomeration in a dc field. We report measurements of the electrical properties of these wires. As the voltage applied across a wire increases the resistance of the wire decreases. At certain voltage settings, a rapid change in the electric current occurred, accompanied by a change in shape of the wire as observed with an optical microscope. The rapid change may result from an increase in wire density when the voltage reaches certain critical values. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360544

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Reasonable consistency between experimental data for the ambipolar diffusion length and experimental data for the photoconductivity is demonstrated for steady‐state measurements performed ona‐Si:H layers. This consistency is obtained based on the ‘‘standard’’ defect model fora‐Si:H. In this model the dangling bonds are taken into account, considering their amphoteric behavior and treating then as recombination centers, whereas the band tails are taken into account as simple two‐valued defects acting as traps. Consistency is obtained based on (1) a particular form of the recombination function such as is considered appropriate for the dangling bonds, as well as, additionally, (2) the local charge neutrality condition. The experimental data analyzed are power laws of the ambipolar diffusion length and of the photoconductivity (versus light intensity); they are obtained for a series of slightlypandn‐doped samples including the undoped case. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360545

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A specially prepared paint made up of lead zirconate titanate (PZT) ceramic powder and epoxy resin was coated on an aluminum plate and was cured at room temperature, thus forming the paint film of 25–300 &mgr;m thickness with a PZT volume fraction of 53%. The paint film was then poled at room temperature, and the poling behavior was determined by measuring the piezoelectric activity as a function of poling field. The poling behavior shows that the piezoelectric activity obtained at a given poling field increases with an increase in the film thickness from 25 to 300 &mgr;m. The current–voltage characteristic of the paint film, on the other hand, shows that the increase in the film thickness leads not only to an increase in the magnitude of the current density at a given electric field but also to an increase in the critical electric field at which the transition from the ohmic to space‐charge‐limited conduction takes place. This fact indicates that the amount of the space charge of electrons injected into the paint film decreases as the film thickness increases. Furthermore, comparison of the current–voltage characteristic of the paint film with that of a pure epoxy film reveals that the space charge is accumulated largely at the interface between the PZT and epoxy phases in the paint film. On the basis of this finding, a model is developed for the poling behavior of the paint film by taking into account a possible effect of the space‐charge accumulation and a broad distribution of the electric field in the PZT phase. This model is shown to give an excellent fit to the experimental data of the piezoelectric activity obtained here as a function of poling field and film thickness. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360546

出版商:AIP    

年代:1995

数据来源: AIP